Cytoplasmic Dynein and Kinesin Power Axonal Transport Schematic diagram of the microtubule motor proteins cytoplasmic dynein and kinesin. Cytoplasmic dynein transports cargo in the retrograde direction toward the minus ends of microtubules whereas kinesin transports cargo in the anterograde direction toward the plus ends. Cytoplasmic dynein is a large multimeric protein complex comprising two heavy chain subunits (red) that possess microtubule binding and ATPase activity, two intermediate chains (yellow), two light intermediate chains (indigo), and an assortment of light chains (light pink, green, orange) (reviewed in [7]). Dynactin, a large multisubunit protein complex of comparable size to cytoplasmic dynein, is proposed to link the dynein motor to cargo and/or increases its processivity. The largest dynactin subunit, p150 Glued (turquoise), forms an elongated dimer that interacts with the dynein intermediate chain and binds to microtubules via a highly conserved CAP-Gly motif at the tip of globular heads. The dynactin subunit p50 (dark pink) occupies a central position linking p150 Glued to cargo. The conventional kinesin holoenzyme, also known as kinesin-1, is a heterotetramer comprising two Khc subunits (red) with microtubule binding and ATPase domains, a central coiled stalk, and a tail domain that interacts with two Klc subunits (green). Klcs may mediate cargo- binding via an intermediate scaffold protein (blue) that binds a cargo transmembrane protein (yellow). 

Cytoplasmic Dynein and Kinesin Power Axonal Transport Schematic diagram of the microtubule motor proteins cytoplasmic dynein and kinesin. Cytoplasmic dynein transports cargo in the retrograde direction toward the minus ends of microtubules whereas kinesin transports cargo in the anterograde direction toward the plus ends. Cytoplasmic dynein is a large multimeric protein complex comprising two heavy chain subunits (red) that possess microtubule binding and ATPase activity, two intermediate chains (yellow), two light intermediate chains (indigo), and an assortment of light chains (light pink, green, orange) (reviewed in [7]). Dynactin, a large multisubunit protein complex of comparable size to cytoplasmic dynein, is proposed to link the dynein motor to cargo and/or increases its processivity. The largest dynactin subunit, p150 Glued (turquoise), forms an elongated dimer that interacts with the dynein intermediate chain and binds to microtubules via a highly conserved CAP-Gly motif at the tip of globular heads. The dynactin subunit p50 (dark pink) occupies a central position linking p150 Glued to cargo. The conventional kinesin holoenzyme, also known as kinesin-1, is a heterotetramer comprising two Khc subunits (red) with microtubule binding and ATPase domains, a central coiled stalk, and a tail domain that interacts with two Klc subunits (green). Klcs may mediate cargo- binding via an intermediate scaffold protein (blue) that binds a cargo transmembrane protein (yellow). 

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Neurons are specialized cells with a complex architecture that includes elaborate dendritic branches and a long, narrow axon that extends from the cell body to the synaptic terminal. The organized transport of essential biological materials throughout the neuron is required to support its growth, function, and viability. In this review, we focus on...

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... are specialized cells with a complex N architecture branches and that a long, includes narrow elaborate axon that dendritic extends from the cell body to the synaptic terminal. The organized transport of essential biological materials throughout the neuron is required to support its growth, function, and viability. In this review, we focus on insights that have emerged from the genetic analysis of long-distance axonal transport between the cell body and the synaptic terminal. We also discuss recent genetic evidence that supports the hypothesis that disruptions in axonal transport may cause or dramatically contribute to neurodegenerative diseases. The axon of a neuron conducts the transmission of action potentials from the cell body to the synapse. The axon also provides a physical conduit for the transport of essential biological materials between the cell body and the synapse that are required for the function and viability of the neuron. A diverse array of cargoes including membranous organelles, synaptic vesicle precursors, signaling molecules, growth factors, protein complexes, cytoskeletal components, and even the sodium and potassium channels required for action potential propagation are actively transported from their site of synthesis in the cell body through the axoplasm to intracellular target sites in the axon and synapse. Simultaneously, neurotrophic signals are transported from the synapse back to the cell body to monitor the integrity of target innervation. The length of axons in the peripheral nervous system can be in excess of one meter in humans, and even longer in larger animals, making these cells particularly reliant on the efficient and coordinated physical transport of materials through the axons for their function and viability. The length and narrow caliber of axons coupled with the amount of material that must be transported raises the possibility that this system might exhibit significant vulnerability to perturbation. It has been proposed that disruptions in axonal transport may lead to axonal transport defects that manifest as a number of different neurodegenerative diseases [1]. In this review, we focus on the use of genetics to understand axonal transport, including the identification and functional characterization of components required for axonal transport, and the biological and medical consequences when these functions are compromised. Simplistically, the axonal transport system comprises cargo, motor proteins that power cargo transport, cytoskeletal filaments or ‘‘ tracks ’’ along which the motors generate force and movement, linker proteins that attach motor proteins to cargo or other cellular structures, and accessory molecules that initiate and regulate transport. Defective axonal transport and neurodegenerative diseases could potentially result from disruptions in any of the components required for axonal transport. Long-distance transport in the axon is primarily a microtubule-dependent process. The microtubule tracks within an axon possess inherent polarity and are uniformly oriented with the fast-growing (plus) ends projecting toward the synapse and the slow-growing (minus) ends toward the cell body [2]. The motor proteins that power axonal transport on microtubules are members of the kinesin and cytoplasmic dynein superfamilies. Kinesins are generally plus-end– directed motor proteins that transport cargoes such as synaptic vesicle precursors and membranous organelles anterogradely toward the synapse (Figure 1). Cytoplasmic dyneins are minus-end–directed motor proteins that transport cargoes including neurotrophic signals, endosomes, and other organelles and vesicles retrogradely toward the cell body (Figure 1). Retrograde transport may not be exclusive to dyneins, however, as a few kinesins that translocate cargo in the retrograde direction have been identified [3,4]. In mammals, the kinesin superfamily consists of approximately 45 members (KIFs) grouped into 14 subfamilies (reviewed in [5]). Kinesins comprise one to four motor polypeptides called heavy chains that contain a highly conserved motor domain, with ATPase and microtubule-binding regions, and a divergent tail domain. Regulatory and/or accessory subunits, such as the kinesin light chain (Klc), are thought to interact with the tail domain of the kinesin heavy chain (Khc) to confer cargo-binding specificity and regulation (Figure 1) (reviewed in [6]). In contrast to kinesin, the cytoplasmic dynein family in mammals is much smaller, consisting of only two members. Cytoplasmic dynein, however, is a larger and more complex microtubule motor, comprising two dynein heavy chain (Dhc) motor subunits and various intermediate, light intermediate, and light chain (Dlc) subunits (Figure 1) (reviewed in [7]). Cytoplasmic dynein appears to employ a ‘‘ subunit heterogeneity ’’ approach to support a wide range of essential cellular functions with only a few copies of the cytoplasmic dynein motor peptide and a diverse array of dynein-associated accessory proteins that impart cargo- binding specificity and functional activity [6,8]. Considerable evidence suggests that dynein function is dependent on an equally large protein complex called dynactin, which is proposed to link cytoplasmic dynein to its cargo and/or to increase dynein processivity through an association with microtubules (Figure 1) [9,10]. Based on the kinetics of transport determined from classic pulse-chase labeling experiments, axonal transport is classified as either fast or slow (reviewed in [11,12]). Fast axonal transport occurs in both the retrograde and anterograde directions at a rate of 0.5–10 l m/sec and includes the transport of membrane-bound organelles, mitochondria, neurotransmitters, channel proteins, multivesicular bodies, and endosomes. In contrast, slow axonal transport occurs in the anterograde direction at a rate of 0.01–0.001 l m/sec, considerably slower than fast axonal transport [12]. Cytoskeletal components, such as neurofilaments, tubulin, and actin, as well as proteins such as clathrin and cytosolic enzymes are transported at this slower rate [12]. Current thought is that slow axonal transport is mediated by the same microtubule motors that participate in fast axonal transport, with fast instantaneous transport of cargo interspersed with prolonged pauses [13–15]. Classic studies using extruded squid axoplasm identified kinesin and cytoplasmic dynein as candidate motors required for axonal transport [16–20]. Since then, many different animal model systems have been used to genetically investigate axonal transport mechanisms. Such studies reveal considerable diversity in kinesin function in the axon (Table 1). The requirement for conventional kinesin (Kinesin-1) in axonal transport was revealed in Drosophila melanogaster larvae with lesions in Khc and Klc genes. These mutants exhibit axonal swellings containing accumulations of transported vesicles, synaptic membranes, and mitochondria [21–23]. Such axonal ‘‘ organelle jams ’’ are a phenotypic hallmark of compromised axonal transport and result in a posterior paralysis of mutant larvae. Loss of function of the ...
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... are specialized cells with a complex N architecture branches and that a long, includes narrow elaborate axon that dendritic extends from the cell body to the synaptic terminal. The organized transport of essential biological materials throughout the neuron is required to support its growth, function, and viability. In this review, we focus on insights that have emerged from the genetic analysis of long-distance axonal transport between the cell body and the synaptic terminal. We also discuss recent genetic evidence that supports the hypothesis that disruptions in axonal transport may cause or dramatically contribute to neurodegenerative diseases. The axon of a neuron conducts the transmission of action potentials from the cell body to the synapse. The axon also provides a physical conduit for the transport of essential biological materials between the cell body and the synapse that are required for the function and viability of the neuron. A diverse array of cargoes including membranous organelles, synaptic vesicle precursors, signaling molecules, growth factors, protein complexes, cytoskeletal components, and even the sodium and potassium channels required for action potential propagation are actively transported from their site of synthesis in the cell body through the axoplasm to intracellular target sites in the axon and synapse. Simultaneously, neurotrophic signals are transported from the synapse back to the cell body to monitor the integrity of target innervation. The length of axons in the peripheral nervous system can be in excess of one meter in humans, and even longer in larger animals, making these cells particularly reliant on the efficient and coordinated physical transport of materials through the axons for their function and viability. The length and narrow caliber of axons coupled with the amount of material that must be transported raises the possibility that this system might exhibit significant vulnerability to perturbation. It has been proposed that disruptions in axonal transport may lead to axonal transport defects that manifest as a number of different neurodegenerative diseases [1]. In this review, we focus on the use of genetics to understand axonal transport, including the identification and functional characterization of components required for axonal transport, and the biological and medical consequences when these functions are compromised. Simplistically, the axonal transport system comprises cargo, motor proteins that power cargo transport, cytoskeletal filaments or ‘‘ tracks ’’ along which the motors generate force and movement, linker proteins that attach motor proteins to cargo or other cellular structures, and accessory molecules that initiate and regulate transport. Defective axonal transport and neurodegenerative diseases could potentially result from disruptions in any of the components required for axonal transport. Long-distance transport in the axon is primarily a microtubule-dependent process. The microtubule tracks within an axon possess inherent polarity and are uniformly oriented with the fast-growing (plus) ends projecting toward the synapse and the slow-growing (minus) ends toward the cell body [2]. The motor proteins that power axonal transport on microtubules are members of the kinesin and cytoplasmic dynein superfamilies. Kinesins are generally plus-end– directed motor proteins that transport cargoes such as synaptic vesicle precursors and membranous organelles anterogradely toward the synapse (Figure 1). Cytoplasmic dyneins are minus-end–directed motor proteins that transport cargoes including neurotrophic signals, endosomes, and other organelles and vesicles retrogradely toward the cell body (Figure 1). Retrograde transport may not be exclusive to dyneins, however, as a few kinesins that translocate cargo in the retrograde direction have been identified [3,4]. In mammals, the kinesin superfamily consists of approximately 45 members (KIFs) grouped into 14 subfamilies (reviewed in [5]). Kinesins comprise one to four motor polypeptides called heavy chains that contain a highly conserved motor domain, with ATPase and microtubule-binding regions, and a divergent tail domain. Regulatory and/or accessory subunits, such as the kinesin light chain (Klc), are thought to interact with the tail domain of the kinesin heavy chain (Khc) to confer cargo-binding specificity and regulation (Figure 1) (reviewed in [6]). In contrast to kinesin, the cytoplasmic dynein family in mammals is much smaller, consisting of only two members. Cytoplasmic dynein, however, is a larger and more complex microtubule motor, comprising two dynein heavy chain (Dhc) motor subunits and various intermediate, light intermediate, and light chain (Dlc) subunits (Figure 1) (reviewed in [7]). Cytoplasmic dynein appears to employ a ‘‘ subunit heterogeneity ’’ approach to support a wide range of essential cellular functions with only a few copies of the cytoplasmic dynein motor peptide and a diverse array of dynein-associated accessory proteins that impart cargo- binding specificity and functional activity [6,8]. Considerable evidence suggests that dynein function is dependent on an equally large protein complex called dynactin, which is proposed to link cytoplasmic dynein to its cargo and/or to increase dynein processivity through an association with microtubules (Figure 1) [9,10]. Based on the kinetics of transport determined from classic pulse-chase labeling experiments, axonal transport is classified as either fast or slow (reviewed in [11,12]). Fast axonal transport occurs in both the retrograde and anterograde directions at a rate of 0.5–10 l m/sec and includes the transport of membrane-bound organelles, mitochondria, neurotransmitters, channel proteins, multivesicular bodies, and endosomes. In contrast, slow axonal transport occurs in the anterograde direction at a rate of 0.01–0.001 l m/sec, considerably slower than fast axonal transport [12]. Cytoskeletal components, such as neurofilaments, tubulin, and actin, as well as proteins such as clathrin and cytosolic enzymes are transported at this slower rate [12]. Current thought is that slow axonal transport is mediated by the same microtubule motors that participate in fast axonal transport, with fast instantaneous transport of cargo interspersed with prolonged pauses [13–15]. Classic studies using extruded squid axoplasm identified kinesin and cytoplasmic dynein as candidate motors required for axonal transport [16–20]. Since then, many different animal model systems have been used to genetically investigate axonal transport mechanisms. Such studies reveal considerable diversity in kinesin function in the axon (Table 1). The requirement for conventional kinesin (Kinesin-1) in axonal transport was revealed in Drosophila melanogaster larvae with lesions in Khc and Klc genes. These mutants exhibit axonal swellings containing accumulations of transported vesicles, synaptic membranes, and mitochondria [21–23]. Such axonal ‘‘ organelle jams ’’ are a phenotypic hallmark of compromised axonal transport and result in a posterior paralysis of mutant larvae. Loss of function of the ...
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... are specialized cells with a complex N architecture branches and that a long, includes narrow elaborate axon that dendritic extends from the cell body to the synaptic terminal. The organized transport of essential biological materials throughout the neuron is required to support its growth, function, and viability. In this review, we focus on insights that have emerged from the genetic analysis of long-distance axonal transport between the cell body and the synaptic terminal. We also discuss recent genetic evidence that supports the hypothesis that disruptions in axonal transport may cause or dramatically contribute to neurodegenerative diseases. The axon of a neuron conducts the transmission of action potentials from the cell body to the synapse. The axon also provides a physical conduit for the transport of essential biological materials between the cell body and the synapse that are required for the function and viability of the neuron. A diverse array of cargoes including membranous organelles, synaptic vesicle precursors, signaling molecules, growth factors, protein complexes, cytoskeletal components, and even the sodium and potassium channels required for action potential propagation are actively transported from their site of synthesis in the cell body through the axoplasm to intracellular target sites in the axon and synapse. Simultaneously, neurotrophic signals are transported from the synapse back to the cell body to monitor the integrity of target innervation. The length of axons in the peripheral nervous system can be in excess of one meter in humans, and even longer in larger animals, making these cells particularly reliant on the efficient and coordinated physical transport of materials through the axons for their function and viability. The length and narrow caliber of axons coupled with the amount of material that must be transported raises the possibility that this system might exhibit significant vulnerability to perturbation. It has been proposed that disruptions in axonal transport may lead to axonal transport defects that manifest as a number of different neurodegenerative diseases [1]. In this review, we focus on the use of genetics to understand axonal transport, including the identification and functional characterization of components required for axonal transport, and the biological and medical consequences when these functions are compromised. Simplistically, the axonal transport system comprises cargo, motor proteins that power cargo transport, cytoskeletal filaments or ‘‘ tracks ’’ along which the motors generate force and movement, linker proteins that attach motor proteins to cargo or other cellular structures, and accessory molecules that initiate and regulate transport. Defective axonal transport and neurodegenerative diseases could potentially result from disruptions in any of the components required for axonal transport. Long-distance transport in the axon is primarily a microtubule-dependent process. The microtubule tracks within an axon possess inherent polarity and are uniformly oriented with the fast-growing (plus) ends projecting toward the synapse and the slow-growing (minus) ends toward the cell body [2]. The motor proteins that power axonal transport on microtubules are members of the kinesin and cytoplasmic dynein superfamilies. Kinesins are generally plus-end– directed motor proteins that transport cargoes such as synaptic vesicle precursors and membranous organelles anterogradely toward the synapse (Figure 1). Cytoplasmic dyneins are minus-end–directed motor proteins that transport cargoes including neurotrophic signals, endosomes, and other organelles and vesicles retrogradely toward the cell body (Figure 1). Retrograde transport may not be exclusive to dyneins, however, as a few kinesins that translocate cargo in the retrograde direction have been identified [3,4]. In mammals, the kinesin superfamily consists of approximately 45 members (KIFs) grouped into 14 subfamilies (reviewed in [5]). Kinesins comprise one to four motor polypeptides called heavy chains that contain a highly conserved motor domain, with ATPase and microtubule-binding regions, and a divergent tail domain. Regulatory and/or accessory subunits, such as the kinesin light chain (Klc), are thought to interact with the tail domain of the kinesin heavy chain (Khc) to confer cargo-binding specificity and regulation (Figure 1) (reviewed in [6]). In contrast to kinesin, the cytoplasmic dynein family in mammals is much smaller, consisting of only two members. Cytoplasmic dynein, however, is a larger and more complex microtubule motor, comprising two dynein heavy chain (Dhc) motor subunits and various intermediate, light intermediate, and light chain (Dlc) subunits (Figure 1) (reviewed in [7]). Cytoplasmic dynein appears to employ a ‘‘ subunit heterogeneity ’’ approach to support a wide range of essential cellular functions with only a few copies of the cytoplasmic dynein motor peptide and a diverse array of dynein-associated accessory proteins that impart cargo- binding specificity and functional activity [6,8]. Considerable evidence suggests that dynein function is dependent on an equally large protein complex called dynactin, which is proposed to link cytoplasmic dynein to its cargo and/or to increase dynein processivity through an association with microtubules (Figure 1) [9,10]. Based on the kinetics of transport determined from classic pulse-chase labeling experiments, axonal transport is classified as either fast or slow (reviewed in [11,12]). Fast axonal transport occurs in both the retrograde and anterograde directions at a rate of 0.5–10 l m/sec and includes the transport of membrane-bound organelles, mitochondria, neurotransmitters, channel proteins, multivesicular bodies, and endosomes. In contrast, slow axonal transport occurs in the anterograde direction at a rate of 0.01–0.001 l m/sec, considerably slower than fast axonal transport [12]. Cytoskeletal components, such as neurofilaments, tubulin, and actin, as well as proteins such as clathrin and cytosolic enzymes are transported at this slower rate [12]. Current thought is that slow axonal transport is mediated by the same microtubule motors that participate in fast axonal transport, with fast instantaneous transport of cargo interspersed with prolonged pauses [13–15]. Classic studies using extruded squid axoplasm identified kinesin and cytoplasmic dynein as candidate motors required for axonal transport [16–20]. Since then, many different animal model systems have been used to genetically investigate axonal transport mechanisms. Such studies reveal considerable diversity in kinesin function in the axon (Table 1). The requirement for conventional kinesin (Kinesin-1) in axonal transport was revealed in Drosophila melanogaster larvae with lesions in Khc and Klc genes. These mutants exhibit axonal swellings containing accumulations of transported vesicles, synaptic membranes, and mitochondria [21–23]. Such axonal ‘‘ organelle jams ’’ are a phenotypic hallmark of compromised axonal transport and result in a posterior paralysis of mutant larvae. Loss of function of the ...
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... are specialized cells with a complex N architecture branches and that a long, includes narrow elaborate axon that dendritic extends from the cell body to the synaptic terminal. The organized transport of essential biological materials throughout the neuron is required to support its growth, function, and viability. In this review, we focus on insights that have emerged from the genetic analysis of long-distance axonal transport between the cell body and the synaptic terminal. We also discuss recent genetic evidence that supports the hypothesis that disruptions in axonal transport may cause or dramatically contribute to neurodegenerative diseases. The axon of a neuron conducts the transmission of action potentials from the cell body to the synapse. The axon also provides a physical conduit for the transport of essential biological materials between the cell body and the synapse that are required for the function and viability of the neuron. A diverse array of cargoes including membranous organelles, synaptic vesicle precursors, signaling molecules, growth factors, protein complexes, cytoskeletal components, and even the sodium and potassium channels required for action potential propagation are actively transported from their site of synthesis in the cell body through the axoplasm to intracellular target sites in the axon and synapse. Simultaneously, neurotrophic signals are transported from the synapse back to the cell body to monitor the integrity of target innervation. The length of axons in the peripheral nervous system can be in excess of one meter in humans, and even longer in larger animals, making these cells particularly reliant on the efficient and coordinated physical transport of materials through the axons for their function and viability. The length and narrow caliber of axons coupled with the amount of material that must be transported raises the possibility that this system might exhibit significant vulnerability to perturbation. It has been proposed that disruptions in axonal transport may lead to axonal transport defects that manifest as a number of different neurodegenerative diseases [1]. In this review, we focus on the use of genetics to understand axonal transport, including the identification and functional characterization of components required for axonal transport, and the biological and medical consequences when these functions are compromised. Simplistically, the axonal transport system comprises cargo, motor proteins that power cargo transport, cytoskeletal filaments or ‘‘ tracks ’’ along which the motors generate force and movement, linker proteins that attach motor proteins to cargo or other cellular structures, and accessory molecules that initiate and regulate transport. Defective axonal transport and neurodegenerative diseases could potentially result from disruptions in any of the components required for axonal transport. Long-distance transport in the axon is primarily a microtubule-dependent process. The microtubule tracks within an axon possess inherent polarity and are uniformly oriented with the fast-growing (plus) ends projecting toward the synapse and the slow-growing (minus) ends toward the cell body [2]. The motor proteins that power axonal transport on microtubules are members of the kinesin and cytoplasmic dynein superfamilies. Kinesins are generally plus-end– directed motor proteins that transport cargoes such as synaptic vesicle precursors and membranous organelles anterogradely toward the synapse (Figure 1). Cytoplasmic dyneins are minus-end–directed motor proteins that transport cargoes including neurotrophic signals, endosomes, and other organelles and vesicles retrogradely toward the cell body (Figure 1). Retrograde transport may not be exclusive to dyneins, however, as a few kinesins that translocate cargo in the retrograde direction have been identified [3,4]. In mammals, the kinesin superfamily consists of approximately 45 members (KIFs) grouped into 14 subfamilies (reviewed in [5]). Kinesins comprise one to four motor polypeptides called heavy chains that contain a highly conserved motor domain, with ATPase and microtubule-binding regions, and a divergent tail domain. Regulatory and/or accessory subunits, such as the kinesin light chain (Klc), are thought to interact with the tail domain of the kinesin heavy chain (Khc) to confer cargo-binding specificity and regulation (Figure 1) (reviewed in [6]). In contrast to kinesin, the cytoplasmic dynein family in mammals is much smaller, consisting of only two members. Cytoplasmic dynein, however, is a larger and more complex microtubule motor, comprising two dynein heavy chain (Dhc) motor subunits and various intermediate, light intermediate, and light chain (Dlc) subunits (Figure 1) (reviewed in [7]). Cytoplasmic dynein appears to employ a ‘‘ subunit heterogeneity ’’ approach to support a wide range of essential cellular functions with only a few copies of the cytoplasmic dynein motor peptide and a diverse array of dynein-associated accessory proteins that impart cargo- binding specificity and functional activity [6,8]. Considerable evidence suggests that dynein function is dependent on an equally large protein complex called dynactin, which is proposed to link cytoplasmic dynein to its cargo and/or to increase dynein processivity through an association with microtubules (Figure 1) [9,10]. Based on the kinetics of transport determined from classic pulse-chase labeling experiments, axonal transport is classified as either fast or slow (reviewed in [11,12]). Fast axonal transport occurs in both the retrograde and anterograde directions at a rate of 0.5–10 l m/sec and includes the transport of membrane-bound organelles, mitochondria, neurotransmitters, channel proteins, multivesicular bodies, and endosomes. In contrast, slow axonal transport occurs in the anterograde direction at a rate of 0.01–0.001 l m/sec, considerably slower than fast axonal transport [12]. Cytoskeletal components, such as neurofilaments, tubulin, and actin, as well as proteins such as clathrin and cytosolic enzymes are transported at this slower rate [12]. Current thought is that slow axonal transport is mediated by the same microtubule motors that participate in fast axonal transport, with fast instantaneous transport of cargo interspersed with prolonged pauses [13–15]. Classic studies using extruded squid axoplasm identified kinesin and cytoplasmic dynein as candidate motors required for axonal transport [16–20]. Since then, many different animal model systems have been used to genetically investigate axonal transport mechanisms. Such studies reveal considerable diversity in kinesin function in the axon (Table 1). The requirement for conventional kinesin (Kinesin-1) in axonal transport was revealed in Drosophila melanogaster larvae with lesions in Khc and Klc genes. These mutants exhibit axonal swellings containing accumulations of transported vesicles, synaptic membranes, and mitochondria [21–23]. Such axonal ‘‘ organelle jams ’’ are a phenotypic hallmark of compromised axonal transport and result in a posterior paralysis of mutant larvae. Loss of function of the ...
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... are specialized cells with a complex N architecture branches and that a long, includes narrow elaborate axon that dendritic extends from the cell body to the synaptic terminal. The organized transport of essential biological materials throughout the neuron is required to support its growth, function, and viability. In this review, we focus on insights that have emerged from the genetic analysis of long-distance axonal transport between the cell body and the synaptic terminal. We also discuss recent genetic evidence that supports the hypothesis that disruptions in axonal transport may cause or dramatically contribute to neurodegenerative diseases. The axon of a neuron conducts the transmission of action potentials from the cell body to the synapse. The axon also provides a physical conduit for the transport of essential biological materials between the cell body and the synapse that are required for the function and viability of the neuron. A diverse array of cargoes including membranous organelles, synaptic vesicle precursors, signaling molecules, growth factors, protein complexes, cytoskeletal components, and even the sodium and potassium channels required for action potential propagation are actively transported from their site of synthesis in the cell body through the axoplasm to intracellular target sites in the axon and synapse. Simultaneously, neurotrophic signals are transported from the synapse back to the cell body to monitor the integrity of target innervation. The length of axons in the peripheral nervous system can be in excess of one meter in humans, and even longer in larger animals, making these cells particularly reliant on the efficient and coordinated physical transport of materials through the axons for their function and viability. The length and narrow caliber of axons coupled with the amount of material that must be transported raises the possibility that this system might exhibit significant vulnerability to perturbation. It has been proposed that disruptions in axonal transport may lead to axonal transport defects that manifest as a number of different neurodegenerative diseases [1]. In this review, we focus on the use of genetics to understand axonal transport, including the identification and functional characterization of components required for axonal transport, and the biological and medical consequences when these functions are compromised. Simplistically, the axonal transport system comprises cargo, motor proteins that power cargo transport, cytoskeletal filaments or ‘‘ tracks ’’ along which the motors generate force and movement, linker proteins that attach motor proteins to cargo or other cellular structures, and accessory molecules that initiate and regulate transport. Defective axonal transport and neurodegenerative diseases could potentially result from disruptions in any of the components required for axonal transport. Long-distance transport in the axon is primarily a microtubule-dependent process. The microtubule tracks within an axon possess inherent polarity and are uniformly oriented with the fast-growing (plus) ends projecting toward the synapse and the slow-growing (minus) ends toward the cell body [2]. The motor proteins that power axonal transport on microtubules are members of the kinesin and cytoplasmic dynein superfamilies. Kinesins are generally plus-end– directed motor proteins that transport cargoes such as synaptic vesicle precursors and membranous organelles anterogradely toward the synapse (Figure 1). Cytoplasmic dyneins are minus-end–directed motor proteins that transport cargoes including neurotrophic signals, endosomes, and other organelles and vesicles retrogradely toward the cell body (Figure 1). Retrograde transport may not be exclusive to dyneins, however, as a few kinesins that translocate cargo in the retrograde direction have been identified [3,4]. In mammals, the kinesin superfamily consists of approximately 45 members (KIFs) grouped into 14 subfamilies (reviewed in [5]). Kinesins comprise one to four motor polypeptides called heavy chains that contain a highly conserved motor domain, with ATPase and microtubule-binding regions, and a divergent tail domain. Regulatory and/or accessory subunits, such as the kinesin light chain (Klc), are thought to interact with the tail domain of the kinesin heavy chain (Khc) to confer cargo-binding specificity and regulation (Figure 1) (reviewed in [6]). In contrast to kinesin, the cytoplasmic dynein family in mammals is much smaller, consisting of only two members. Cytoplasmic dynein, however, is a larger and more complex microtubule motor, comprising two dynein heavy chain (Dhc) motor subunits and various intermediate, light intermediate, and light chain (Dlc) subunits (Figure 1) (reviewed in [7]). Cytoplasmic dynein appears to employ a ‘‘ subunit heterogeneity ’’ approach to support a wide range of essential cellular functions with only a few copies of the cytoplasmic dynein motor peptide and a diverse array of dynein-associated accessory proteins that impart cargo- binding specificity and functional activity [6,8]. Considerable evidence suggests that dynein function is dependent on an equally large protein complex called dynactin, which is proposed to link cytoplasmic dynein to its cargo and/or to increase dynein processivity through an association with microtubules (Figure 1) [9,10]. Based on the kinetics of transport determined from classic pulse-chase labeling experiments, axonal transport is classified as either fast or slow (reviewed in [11,12]). Fast axonal transport occurs in both the retrograde and anterograde directions at a rate of 0.5–10 l m/sec and includes the transport of membrane-bound organelles, mitochondria, neurotransmitters, channel proteins, multivesicular bodies, and endosomes. In contrast, slow axonal transport occurs in the anterograde direction at a rate of 0.01–0.001 l m/sec, considerably slower than fast axonal transport [12]. Cytoskeletal components, such as neurofilaments, tubulin, and actin, as well as proteins such as clathrin and cytosolic enzymes are transported at this slower rate [12]. Current thought is that slow axonal transport is mediated by the same microtubule motors that participate in fast axonal transport, with fast instantaneous transport of cargo interspersed with prolonged pauses [13–15]. Classic studies using extruded squid axoplasm identified kinesin and cytoplasmic dynein as candidate motors required for axonal transport [16–20]. Since then, many different animal model systems have been used to genetically investigate axonal transport mechanisms. Such studies reveal considerable diversity in kinesin function in the axon (Table 1). The requirement for conventional kinesin (Kinesin-1) in axonal transport was revealed in Drosophila melanogaster larvae with lesions in Khc and Klc genes. These mutants exhibit axonal swellings containing accumulations of transported vesicles, synaptic membranes, and mitochondria [21–23]. Such axonal ‘‘ organelle jams ’’ are a phenotypic hallmark of compromised axonal transport and result in a posterior paralysis of mutant larvae. Loss of function of the ...
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... dynein and dynactin in motor neurons, and motor neuron degeneration [43,44]. Three additional lesions in the p150 Glued subunit of dynactin have also been identified in patients with amyotrophic lateral sclerosis [45]. Motor proteins bind to transmembrane proteins on the cargo surface directly, or indirectly, via intermediary scaffold proteins ( Figure 1) [6,46]. The cJun NH 2 -terminal kinase (JNK) interacting protein (JIP) group is a class of proteins that may link the kinesin motor to cargo and also act as a scaffold for components of the stress-activated JNK kinase signaling pathway [47]. This implies that the subcellular localization of the JNK signaling complex in the neuron may be regulated by vesicular axonal transport or conversely that kinesin motor activity during axonal transport may itself be regulated via the JNK signaling pathway. In support of the latter, deletion of JNK and JNK kinase results in the mislocalization of synaptic vesicle components in C. elegans [48], although this could be due to a requirement of JNK to regulate microtubule dynamics [49]. The JIP1 and JIP2 proteins are thought to link kinesin with apolipoprotein E receptor 2 (ApoER2) on cargo [50,51]. Aplip1, the Drosophila JIP1 homolog, is required in axonal vesicle transport and, curiously, the retrograde transport of mitochondria [52]. Sunday Driver (Syd)/JIP3 was identified in Drosophila as a scaffold protein possibly required for the interaction of kinesin with vesicles transported in the axon [53]. Interestingly, Syd/JIP3 is implicated as a transport-dependent positive-injury signal in the response to axonal damage [54]. Another interesting process was recently found in studies of the motor domain of KIF5 which has been suggested to interpret variations in microtubule structure in the neuronal cell body to ensure that cargo is directed into the axon [55]. The mechanism by which this occurs is unclear, but microtubule-associated proteins on the surface of microtubules are probable candidates. The predominant microtubule-associated protein in the axon is tau, which promotes microtubule assembly and stability. Mutations in tau not only impair its ability to bind, stabilize, and assemble microtubules [56,57], but also retard its slow transport in the axon [58]. When tau is overexpressed [59,60] or abnormally phosphorylated [61,62], it forms aggregates that may physically block the fast anterograde transport of mitochondria, neurofilaments, peroxisomes, and vesicles carrying the amyloid precursor protein (APP). The retrograde axonal transport of signaling endosomes that provide neurotrophic support for the neuron may also be blocked and prevented from reaching the cell body [63]. The Drosophila proteins Milton and mitochondrial GTPase Miro are also required for the transport of mitochondria [64– 66]. Lesions in Milton and Miro result in the specific failure of mitochondria to be transported anterogradely, and they consequently accumulate in the cell body, although the transport of synaptic vesicles is unaffected. Defects in axonal transport have been indirectly linked to a number of progressive human neurodegenerative diseases including Alzheimer disease (AD), Huntington disease (HD), and amyotrophic lateral sclerosis (ALS). One common feature of these diseases is that the proteins encoded by genes linked to each disease are transported in the axon and can perturb transport when manipulated; presenilin 1 and APP in AD, Cu/ Zn superoxide dismutase (SOD1) in ALS, and huntingtin (Htt) in HD. Each disease is characterized by accumulations of these or other proteins within axons, similar to defective axonal transport phenotypes observed in animal models of motor protein mutants. The pathological hallmarks of AD include neurofibrillary tangles of abnormally phosphorylated tau protein and aggregates of amyloid- b (A b ) peptide resulting in neuritic plaques in the brain [67]. The transmembrane protein APP, the precursor of potentially neurotoxic A b , is transported anterogradely within vesicles in axons by the fast axonal transport system [68]. Interestingly, APP may link the kinesin motor either directly, or indirectly, via the JIP1 scaffold, to a specific class of synaptic vesicles containing synapsin 1, growth-associated protein 43 (GAP-43), along with b secretase and presenilin 1, two components responsible for processing A b from APP [69,70]. Deletion of the APP homolog Appl in Drosophila results in defective axonal transport including axonal accumulation phenotypes [71]. Overexpression of human APP causes similar phenotypes that are enhanced by genetic reduction in kinesin and suppressed by genetic reduction in cytoplasmic dynein [71]. These findings suggest that APP plays a central role in the axonal transport of a specific class of vesicle and that disruption in this transport, through lesions in APP or APP- interacting components, may result in axonal blockages, a possible causative factor in the development of AD. HD is a progressive neurodegenerative disorder caused by expansion of CAG triplet repeats in the coding sequence of the huntingtin gene resulting in an expanded polyglutamine tract (polyQ) in the Htt protein and a toxic gain of function. Interestingly, both Htt and the Huntingtin-associated protein 1 (HAP1) are anterogradely and retrogradely transported in axons [72]. HAP1 interacts with the anterograde motor kinesin via the Klc subunit and is thought to interact with the retrograde motor cytoplasmic dynein through an association with the p150 Glued subunit of dynactin [73–75]. Recent studies raise the possibility of a link between axonal transport defects and the onset of HD. In Drosophila, both a reduction of Htt protein and the overexpression of proteins containing polyQ repeats result in axonal transport defects [76]. Full-length mutant Htt also impairs vesicular and mitochondrial transport in mouse neurons [77]. Although the mechanism of axonal transport disruption remains unclear, one possibility is that toxic Htt titrates soluble motor protein components into axonal aggregates that physically block transport. One class of vesicle potentially affected are those containing brain- derived neurotrophic factor which would result in loss of neurotrophic support and neuronal toxicity [77,78]. Interestingly, in transport studies performed on extruded squid axoplasm, recombinant Htt fragments with polyQ expansions inhibited fast axonal transport in the absence of aggregate formation [79]. This suggests that polyQ aggregates may not be necessary for axonal transport disruption, but may contribute to or enhance neuronal toxicity. Clearly, a more comprehensive analysis is required to elucidate the mechanism of polyQ toxicity. Lesions in the ubiquitously expressed enzyme SOD1 are a cause of rare hereditary ALS [80,81]. Mouse models of hereditary ALS have been generated by transgenic expression of mutant SOD1. These animals have impaired slow axonal transport with axonal accumulations of neurofilaments and tubulin [82–85]. Similarly, large axonal swellings with neurofilament accumulations, consistent with a failure in axonal transport, are observed in patients with ALS [86,87]. It has been suggested that SOD1 may specifically inhibit retrograde axonal transport [88]. The potential involvement of cytoplasmic dynein in ALS was further highlighted by the identification of a number of lesions in the motor binding domain of dynactin subunit p150 Glued in ALS patients [45]. Additional support comes from the observation that the cytoplasmic dynein mutations Loa and Cra1 revert axonal transport defects of ALS mice, attenuating motor neuron degeneration resulting in delayed onset of disease and extended lifespan [89,90]. Although a potential link between axonal transport disorders and neurodegenerative disease has been suggested, a number of critical questions remain unanswered. For example, recent evidence indicates that axonal transport is disrupted in mouse models of ALS, HD, and AD long before detectable pathological hallmarks of the disease are observed [77,83,91]. Similarly, comparable pathology may exist early in these human diseases. Yet, it remains unclear whether these changes are causes or consequences of the disease process. Unraveling these issues will require a better understanding of how axonal transport is controlled and which components contribute to the various pathways. In several cases, it is not known whether human mutations represent loss of function or give rise to dominant negative effects, resulting in toxic proteins that titrate or poison axonal transport components. As a result, the effect on axonal transport could be specific and cause the disruption of only a single class of transported material, or nonspecific and reduce or physically block multiple transport pathways through the aggregation of transported cargoes into axonal blockages. It is likely that both mechanisms occur, depending on the nature of the lesion and the motor component involved. Finally, while genetics in model systems will continue to clarify mechanisms, further investigations of heritable neurological disorders in humans may lead to the identification of additional motor proteins or accessory components required for axonal transport. In any event, a more comprehensive understanding of axonal transport may lead to the development of novel therapies for the treatment of neurodegenerative disorders. ...

Citations

... Dynactin 1, which binds to microtubules, is a motor protein responsible for the retrograde transport of various proteins and vesicles [270]. ALS and slowly progressing, autosomal dominant, distal hereditary motor neuropathy in vocal paresis are due to loss-of-function mutations in dynactin 1 [271][272][273]. ...
Article
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Amyotrophic lateral sclerosis (ALS) is an intractable disease that causes respiratory failure leading to mortality. The main locus of ALS is motor neurons. The success of antisense oligonucleotide (ASO) therapy in spinal muscular atrophy (SMA), a motor neuron disease, has triggered a paradigm shift in developing ALS therapies. The causative genes of ALS and disease-modifying genes, including those of sporadic ALS, have been identified one after another. Thus, the freedom of target choice for gene therapy has expanded by ASO strategy, leading to new avenues for therapeutic development. Tofersen for superoxide dismutase 1 (SOD1) was a pioneer in developing ASO for ALS. Improving protocols and devising early interventions for the disease are vital. In this review, we updated the knowledge of causative genes in ALS. We summarized the genetic mutations identified in familial ALS and their clinical features, focusing on SOD1, fused in sarcoma (FUS), and transacting response DNA-binding protein. The frequency of the C9ORF72 mutation is low in Japan, unlike in Europe and the United States, while SOD1 and FUS are more common, indicating that the target mutations for gene therapy vary by ethnicity. A genome-wide association study has revealed disease-modifying genes, which could be the novel target of gene therapy. The current status and prospects of gene therapy development were discussed, including ethical issues. Furthermore, we discussed the potential of axonal pathology as new therapeutic targets of ALS from the perspective of early intervention, including intra-axonal transcription factors, neuromuscular junction disconnection, dysregulated local translation, abnormal protein degradation, mitochondrial pathology, impaired axonal transport, aberrant cytoskeleton, and axon branching. We simultaneously discuss important pathological states of cell bodies: persistent stress granules, disrupted nucleocytoplasmic transport, and cryptic splicing. The development of gene therapy based on the elucidation of disease-modifying genes and early intervention in molecular pathology is expected to become an important therapeutic strategy in ALS.
... Scaffold proteins can act as adaptors and also bind to members of the mitogen-activated protein family of kinases (MAPKs) (Dhanasekaran et al., 2007). For example, the MAPK-associated scaffold protein, JIP3/Sunday Driver, binds to kinesin-1 and has an evolutionarily conserved role in the axonal transport of synapsedirected vesicles (Cockburn et al., 2018;Duncan and Goldstein, 2006). Similarly, the scaffold protein JIP1 can bind to kinesin-1 (Fu and Holzbaur, 2014), and also to the GluA4 AMPAR subunit (Vieira et al., 2010); however, a role for JIP1 in AMPAR transport has not been established. ...
Article
Synaptic plasticity depends on rapid experience-dependent changes in the number of neurotransmitter receptors. Previously, we demonstrated that motor-mediated transport of AMPA receptors (AMPARs) to and from synapses is a critical determinant of synaptic strength. Here, we describe two convergent signaling pathways that coordinate the loading of synaptic AMPARs onto scaffolds, and scaffolds onto motors, thus providing a mechanism for experience-dependent changes in synaptic strength. We find that an evolutionarily conserved JIP-protein scaffold complex and two classes of mitogen-activated protein kinase (MAPK) proteins mediate AMPAR transport by kinesin-1 motors. Genetic analysis combined with in vivo, real-time imaging in Caenorhabditis elegans revealed that CaMKII is required for loading AMPARs onto the scaffold, and MAPK signaling is required for loading the scaffold complex onto motors. Our data support a model where CaMKII signaling and a MAPK-signaling pathway cooperate to facilitate the rapid exchange of AMPARs required for early stages of synaptic plasticity.
... This motor protein is only responsible for movement along the microtubule and cannot bind to cargo. Another protein called dynactin can bind to the cargo (Duncan & Goldstein, 2006). Then dynactin binds to dynein and transports the dynein protein and cargo like a tow truck (Fig. 8). ...
Article
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Introduction Like other cells in the body, nerve cells need many proteins and substances to maintain homeostasis. As we know, the transcription and translation of proteins and necessary cellular substances occurs in the cell nucleus. The nucleus of nerve cell is located in the cell body. Another part of the nerve cell is "Axon", which has a long structure. Even in some nerve cells axon's length reaches up to 1000 mm. On the other hand, all parts of the neuron need substances and proteins synthesized in nucleus locating in the cell body. Therefore, a mechanism is necessary to express the movement of materials from nucleus along the axon. The movement of materials along the axon is called 'Axoplasmic Transport'. It seems that disturbances in axoplasmic transport can cause various neuronal problems. The purpose of this study is to investigate the mechanism of axoplasmic transport and its types; moreover, the possible effect of exercise on this transition will be discussed.
... Kinesins are a large family of 45 proteins that form the molecular motors responsible for anterograde axonal transport directed by the (+) end of the microtubule [26]. The kinesin-1 motor consists of a kinesin heavy chain dimer, encoded by KIF5A, KIF5B and KIF5C, as well as a dimer of kinesin light chains [27]. Kinesin motors facilitate the anterograde transport of synaptic vesicles, mitochondria, ion channels, adhesion molecules and mRNA from the cell body toward synaptic terminals and into the growth cone [13,25]. ...
... For instance, the adaptor proteins Miro and Milton are necessary to anchor mitochondria to the anterograde motor kinesin-1 [28], whilst numerous adaptor proteins are thought to be involved in binding mitochondria to dynein for retrograde transport [4], although the precise mechanisms for mitochondrial tethering remain unclear. In retrograde transport, the function of dynein is dependent on the dynactin complex (includes proteins encoded by DCTN 1/2) as it links cytoplasmic dynein to its cargo and regulates dynein activity [25,27]. Additionally, the activity of kinases, phosphatases, Rab-GTPases and Ca 2+ concentrations also regulate the cargo-motor associations [14]. ...
Article
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Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by selective, early degeneration of motor neurons in the brain and spinal cord. Motor neurons have long axonal projections, which rely on the integrity of neuronal cytoskeleton and mitochondria to regulate energy requirements for maintaining axonal stability, anterograde and retrograde transport, and signaling between neurons. The formation of protein aggregates which contain cytoskeletal proteins, and mitochondrial dysfunction both have devastating effects on the function of neurons and are shared pathological features across several neurodegenerative conditions, including ALS, Alzheimer's disease, Parkinson's disease, Huntington’s disease and Charcot-Marie-Tooth disease. Furthermore, it is becoming increasingly clear that cytoskeletal integrity and mitochondrial function are intricately linked. Therefore, dysregulations of the cytoskeletal network and mitochondrial homeostasis and localization, may be common pathways in the initial steps of neurodegeneration. Here we review and discuss known contributors, including variants in genetic loci and aberrant protein activities, which modify cytoskeletal integrity, axonal transport and mitochondrial localization in ALS and have overlapping features with other neurodegenerative diseases. Additionally, we explore some emerging pathways that may contribute to this disruption in ALS.
... Kinesins are a large family of 45 proteins that form the molecular motors responsible for anterograde axonal transport directed by the (+) end of the microtubule [26]. The kinesin-1 motor consists of a kinesin heavy chain dimer, encoded by KIF5A, KIF5B and KIF5C, as well as a dimer of kinesin light chains [27]. Kinesin motors facilitate the anterograde transport of synaptic vesicles, mitochondria, ion channels, adhesion molecules and mRNA from the cell body toward synaptic terminals and into the growth cone [13,25]. ...
... For instance, the adaptor proteins Miro and Milton are necessary to anchor mitochondria to the anterograde motor kinesin-1 [28], whilst numerous adaptor proteins are thought to be involved in binding mitochondria to dynein for retrograde transport [4], although the precise mechanisms for mitochondrial tethering remain unclear. In retrograde transport, the function of dynein is dependent on the dynactin complex (includes proteins encoded by DCTN 1/2) as it links cytoplasmic dynein to its cargo and regulates dynein activity [25,27]. Additionally, the activity of kinases, phosphatases, Rab-GTPases and Ca 2+ concentrations also regulate the cargo-motor associations [14]. ...
... Le déplacement effectué par les kinésines est souvent appelé antérograde alors que celui des dynéines est appelé rétrograde. (Duncan and Goldstein, 2006) Chez les mammifères, 45 kinésines ont été identifiées et classées en 14 groupes (Miki et al., 2001 (Figure 7, marquées en rouge) ainsi que plusieurs chaines intermédiaires, intermédiaires légères et légères (Figure 7, marquées en jaune, rose clair, vert, orange et indigo). La dynactine est un grand complexe protéique qui permet la liaison de dynéine à sa cargaison ou bien de renforcer cette liaison. ...
... La plus grande sous-unité de la dynactine est p150 Glued qui interagit avec la dynactine au niveau des chaines intermédiaires et avec les MTs par leurs motifs CAP-Gly (Figure 7, marqué en turquoise). Une autre sous-unité de dynactine est p50 qui lie p150 Glued au cargo (Figure 7, marqué en rose) (Duncan and Goldstein, 2006). La dynactine accroît le déplacement processif de la dynéine sur les MTs, c'est-à-dire sa capacité à faire de nombreux pas consécutifs sans se décrocher (King and Schroer, 2000). ...
Thesis
Les septines, une famille de GTPases qui s’oligomérisent en filaments, forment un nouvel élément du cytosquelette. Principalement alignés avec l'actine corticale et les fibres de stress en condition basale, les filaments de septines peuvent aussi s’associer intégralement aux microtubules (MT), notamment en réponse à un traitement par les taxanes, des molécules stabilisatrices de MT utilisées en chimiothérapie. Les travaux de cette thèse visent à mieux comprendre les mécanismes moléculaires qui contrôlent l’association des filaments de septines avec les autres éléments du cytosquelette, comme en réponse aux taxanes. La résistance des cellules tumorales aux taxanes limite leur emploi en clinique. Mon équipe a mis en évidence un nouveau mécanisme de résistance développé par des cellules adaptées au long cours au paclitaxel, dans lequel la relocalisation des filaments de septines, des fibres de stress vers les MT augmente leur dynamique, contrecarrant ainsi l'effet stabilisateur du paclitaxel. Pendant ma thèse, j’ai montré que, comme dans le cas de l’adaptation à long terme, un traitement aigu par le paclitaxel induit rapidement, une relocalisation complète des filaments de septines, de l’actine vers les MT. Ceci conduit les cellules initialement sensibles à développer une résistance au paclitaxel. Le co-alignement des filaments de septines et des MT ne résulte pas de la stabilisation des MT par le paclitaxel mais ne s’observe que chez les lignées qui expriment un niveau basal élevé de SEPT9_i1. Cette isoforme, connue pour être de mauvais pronostic, est nécessaire mais insuffisante pour le changement de localisation des septines. En cherchant des déterminants moléculaires impliqués dans cette relocalisation, j’ai établi que la protéine BORG2, effectrice de Cdc42 qui lie les septines à l'actine dans les cellules en interphase, est rapidement dégradée par le protéasome suite à un traitement par le paclitaxel. En l’absence de tout traitement, l’inhibition d’expression de BORG2 mime les effets du paclitaxel en induisant le détachement des filaments de septines des fibres de stress et leur relocalisation le long des MT, ainsi qu’une résistance à la drogue. À l'inverse, la surexpression de BORG2 maintient les septines sur les fibres d'actine même après un traitement par le paclitaxel, sans affecter la sensibilité à ce taxane. De façon intéressante, le paclitaxel inhibe partiellement Cdc42, entraînant une baisse de BORG2 et la relocalisation des filaments de septines. Ce phénotype est aussi observé après surexpression d'un mutant inactif de Cdc42, tandis que l'expression d'un mutant constitutivement actif se liant partiellement aux fibres de stress, maintient un niveau d’expression suffisant de BORG2 pour retenir les septines sur l’actine, même après un traitement par le paclitaxel. Ces résultats révèlent les rôles de Cdc42 et de BORG2 dans le contrôle de l'interaction entre les filaments de septines, les fibres d'actine et les MT en condition basale et en réponse aux taxanes. Par ailleurs, après avoir observé, en dehors de tout traitement, que la dépolymérisation des MT provoque une disparition complète des filaments de septines même lorsqu’ils sont associés à l’actine, j’ai exploré le rôle des MT dans l’adressage des septines sur les filaments d'actine. Des résultats préliminaires montrent qu’après inhibition du complexe moteur dynéine/dynactine, les septines colocalisent avec les MT. A l’état basal, le trafic intracellulaire dépendant des MT semble donc jouer un rôle dans l’adressage des filaments de septines aux fibres d’actine. En conclusion, mon travail a permis de mettre en évidence des acteurs clés de la régulation de la compartimentation subcellulaire des filaments de septines, à l’état basal et en réponse aux taxanes : SEPT9_i1, BORG2, Cdc42 ainsi que certains moteurs moléculaires associés aux MT.
... Microtubules provide the platforms for proper intracellular transport by allowing motor proteins to interact with them [51]. While kinesins transport cargoes in the anterograde direction, dyneins are carrying cargoes in the retrograde direction [52]. Upon microtubule binding, tau is involved in the regulation of axonal transport, where tau modulates the motility of kinesin and dynein. ...
Article
Full-text available
Abnormal tau protein aggregation in the brain is a hallmark of tauopathies, such as frontotemporal lobar degeneration and Alzheimer’s disease. Substantial evidence has been linking tau to neurodegeneration, but the underlying mechanisms have yet to be clearly identified. Mitochondria are paramount organelles in neurons, as they provide the main source of energy (adenosine triphosphate) to these highly energetic cells. Mitochondrial dysfunction was identified as an early event of neurodegenerative diseases occurring even before the cognitive deficits. Tau protein was shown to interact with mitochondrial proteins and to impair mitochondrial bioenergetics and dynamics, leading to neurotoxicity. In this review, we discuss in detail the different impacts of disease-associated tau protein on mitochondrial functions, including mitochondrial transport, network dynamics, mitophagy and bioenergetics. We also give new insights about the effects of abnormal tau protein on mitochondrial neurosteroidogenesis, as well as on the endoplasmic reticulum-mitochondria coupling. A better understanding of the pathomechanisms of abnormal tau-induced mitochondrial failure may help to identify new targets for therapeutic interventions.
... On compte 50 kinésines réparties en 14 familles (Endow et al., 2010). Leurs sites de liaisons de l'ATP et des microtubules se situent dans la même région (Vale and Fletterick, 1997 (Duncan and Goldstein, 2006). Si le domaine moteur des kinésines est situé en N-terminal, la kinésine ira préférentiellement vers les bouts (+). ...
... Elles sont composées de deux chaînes lourdes contenant le domaine de liaison aux microtubules et l'activité ATPase, deux chaînes intermédiaires, deux chaînes légères intermédiaires et plusieurs chaînes légères (Duncan and Goldstein, 2006). Elles utilisent également l'ATP pour leur déplacement mais elles ne vont que vers les bouts (-) des microtubules, on parle de mouvement rétrograde (Kardon and Vale, 2009;Wang et al., 1995). ...
... Pour avoir un fonctionnement optimal de la dynéine, il faut une autre protéine, la dynactine (Boylan et al., 2000;Gill et al., 1991) qui permet de lier la dynéine au cargo et d'augmenter son efficacité (Duncan and Goldstein, 2006). La dynactine agit comme un adaptateur permettant à la dynéine de déplacer un groupe plus diversifié de cargos (Karki and Holzbaur, 1999). ...
Thesis
Full-text available
Skeletal muscle is a complex tissue made up of many muscle cells. When a motor neuron in contact with muscle cells, emits an action potential, it propagates along the plasma membrane where it allows the activation of the calcium release complex (CRC), the massive calcium release of terminal cisternae of the sarcoplasmic reticulum (SR) in the cytosol, and thus muscle contraction. This mechanism, called excitation-contraction coupling, requires a specific site of contact between the plasma membrane and the RS, called the triad. More precisely, a triad is composed of an invagination of the plasma membrane, the T-tubule, flanked by two terminal cisternae of the SR. At the triads, the CRC is centered on two calcium channels, the Dihydropyridine Receptor (DHPR) and the Ryanodine Receptor (RyR1), very precisely located face to face in their respective membranes: the T-tubule membrane and the membrane of the SR. Thus, when the membrane is depolarized, the DHPR undergoes a conformational change allowing the opening of RyR1 channel and the release of the calcium. CRC also contains other triad-specific proteins such as calsequestrin or triadin, which have key roles in modulating calcium release. Initiation of contraction thus depends on the precise contact between the SR membranes and the T-tubule membranes and also the exclusive localization of the CRC proteins at the triads. Nevertheless, the mechanisms underlying the precise organization of CRC proteins to the triad remain unknown.During this work, we focused on triadin, a CRC protein that would anchor other CRC proteins through the different interactions it has with RyR1, with calsequestrin and also with microtubules. We studied the mechanisms of trafficking and retention of triadin during muscle differentiation. To do this, the dynamics of triadin was explored by microscopy techniques and by reintroducing, using lentivirus, fluorescent triadin chimeras into differentiated muscle cells.Firstly, the study of CRC proteins targeting and retention in the triad revealed that triadin would take a vesicular pathway to exit the reticulum and reach the triads. This vesicular trafficking pathway would use the microtubule cytoskeleton and in particular the molecular motors and could be a pathway specific to skeletal muscle. In a second step and in later stages of differentiation, triadin would diffuse into SR membranes followed by its accumulation at the triads. Both mechanisms, diffusion and vesicular trafficking, could, however, coexist in a muscle cell. In all cases, once the triad is reached, triadin would be retained thanks to its transmembrane domain. Moreover, I also had the opportunity to take part in a project on the involvement of the MAP6 protein in muscle function. This project has shown that MAP6 is present in skeletal muscle and that its absence leads to muscle weakness associated with a decrease in calcium releases, as well as an impairment of the microtubule network and the organization of SR.
... On compte 50 kinésines réparties en 14 familles (Endow et al., 2010). Leurs sites de liaisons de l'ATP et des microtubules se situent dans la même région (Vale and Fletterick, 1997 (Duncan and Goldstein, 2006). Si le domaine moteur des kinésines est situé en N-terminal, la kinésine ira préférentiellement vers les bouts (+). ...
... Elles sont composées de deux chaînes lourdes contenant le domaine de liaison aux microtubules et l'activité ATPase, deux chaînes intermédiaires, deux chaînes légères intermédiaires et plusieurs chaînes légères (Duncan and Goldstein, 2006). Elles utilisent également l'ATP pour leur déplacement mais elles ne vont que vers les bouts (-) des microtubules, on parle de mouvement rétrograde (Kardon and Vale, 2009;Wang et al., 1995). ...
... Pour avoir un fonctionnement optimal de la dynéine, il faut une autre protéine, la dynactine (Boylan et al., 2000;Gill et al., 1991) qui permet de lier la dynéine au cargo et d'augmenter son efficacité (Duncan and Goldstein, 2006). La dynactine agit comme un adaptateur permettant à la dynéine de déplacer un groupe plus diversifié de cargos (Karki and Holzbaur, 1999). ...
Thesis
Le muscle squelettique est un tissu complexe constitué de nombreuses cellules musculaires. Lorsqu’un motoneurone en contact avec ces cellules, émet un potentiel d’action, celui-ci se propage le long de la membrane plasmique où il permet l’activation du complexe de relâchement du calcium (CRC), la sortie massive de calcium des citernes terminales du réticulum sarcoplasmique (RS) dans le cytosol, et ainsi la contraction musculaire. Ce mécanisme, appelé couplage excitation-contraction, requière un site de contact spécifique entre la membrane plasmique et le RS, appelé triade. Cette dernière est composée d’une invagination de la membrane plasmique, le tubule-t, flanquée de deux citernes terminales du RS. Au sein des triades, le CRC est centré autour de deux canaux calciques, le récepteur des Dihydropyridines (DHPR) et le récepteur de la Ryanodine (RyR1), très précisément localisés face à face dans leurs membranes respectives : la membrane du tubule-t et la membrane du RS. Ainsi, quand la membrane est dépolarisée, le DHPR subit un changement de conformation permettant l’ouverture du canal RyR1 et la sortie du calcium. Le CRC contient également d’autres protéines précisément localisées à la triade comme la calséquestrine ou la triadine, ayant des rôles clés pour moduler la libération du calcium. L’initiation de la contraction dépend ainsi du contact précis entre la membrane du RS et la membrane du tubule-t et également de la localisation exclusive des protéines du CRC au sein de la triade. Néanmoins, les mécanismes sous-jacents à l’organisation précise des protéines du CRC à la triade, restent inconnus.Durant cette thèse, nous nous sommes focalisés sur la triadine protéine du CRC qui servirait d’ancre aux autres protéines du CRC grâce à ses différentes interactions. Nous avons étudié les mécanismes de trafic et de rétention de la triadine au cours de la différenciation musculaire. Pour ce faire, la dynamique de la triadine a été explorée par des techniques de microscopie et en réintroduisant, grâce à des lentivirus, des chimères fluorescentes de triadine au sein de cellules musculaires différenciées.Dans un premier temps l’étude de l’adressage et de la rétention des protéines du CRC à la triade a révélé que la triadine emprunterait une voie vésiculaire pour sortir du reticulum et atteindre les triades. Cette voie de trafic vésiculaire utiliserait le cytosquelette de microtubules et notamment les moteurs moléculaires et pourrait être une voie spécifique au muscle squelettique. Dans un deuxième temps et dans des étapes plus tardives de la différenciation, la triadine diffuserait dans les membranes du RS suivie de son accumulation aux triades. Les deux mécanismes, diffusion et trafic vésiculaire, pourraient cependant coexister dans une cellule musculaire. Dans tous les cas, une fois la triade atteinte, la triadine y serait retenue grâce à son domaine transmembranaire. Durant ma thèse, j’ai également eu l’opportunité de prendre part à un projet portant sur l’implication de la protéine MAP6 dans la fonction musculaire. Ce projet a permis de montrer que MAP6 est bien présente dans le muscle squelettique et que son absence donne lieu à une faiblesse musculaire due en partie à une diminution des relâchements calciques, ainsi qu’à une altération du réseau de microtubules et de l’organisation du RS.
... Many animal models for neurodegenerative disease that resemble human late-onset neurodegenerative diseases are associated with an increase in the number of stalled MBOs, MBOs that travel shorter distances before stalling, and a decrease in the number of transported MBOs (Gunawardena and Goldstein, 2001;Stamer et al., 2002;Pigino et al., 2003;White et al., 2015;Kreiter et al., 2018). Transport defects in models of late-onset neurodegeneration may arise from three different processes: (i) a slow buildup of reduced MBO transport (Williamson and Cleveland, 1999;Duncan and Goldstein, 2006), (ii) an increase in intracellular viscosity with age ( Figure 4B) (Lamoureux et al., 2010), and (iii) a loss in regulation of the transport machinery ( Figure 4A) (Morfini et al., 2009b;Falzone et al., 2010). These altered processes can, independently or synergistically with increased physical crowding, contribute to the progressive nature of the disease with aging. ...
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High concentration of cytoskeletal filaments, organelles, and proteins along with the space constraints due to the axon’s narrow geometry lead inevitably to intracellular physical crowding along the axon of a neuron. Local cargo movement is essential for maintaining steady cargo transport in the axon, and this may be impeded by physical crowding. Molecular motors that mediate active transport share movement mechanisms that allow them to bypass physical crowding present on microtubule tracks. Many neurodegenerative diseases, irrespective of how they are initiated, show increased physical crowding owing to the greater number of stalled organelles and structural changes associated with the cytoskeleton. Increased physical crowding may be a significant factor in slowing cargo transport to synapses, contributing to disease progression and culminating in the dying back of the neuronal process. This review explores the idea that physical crowding can impede cargo movement along the neuronal process. We examine the sources of physical crowding and strategies used by molecular motors that might enable cargo to circumvent physically crowded locations. Finally, we describe sub-cellular changes in neurodegenerative diseases that may alter physical crowding and discuss the implications of such changes on cargo movement.