Annette Gaertner
Research interests
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InterestsNervous system development neuronal polarity, Developmental Neurobiology
Other
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Languagesgerman, english, italian
Publications
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8.99Impact points
N-cadherin specifies first asymmetry in developing neurons.
The EMBO journal. 02/2012;
The precise polarization and orientation of developing neurons is essential for the correct wiring of the brain. In pyramidal excitatory neurons, polarization begins with the sprouting of opposite neurites, which later define directed migration and axo-dendritic domains. We here show that endogenous... [more] The precise polarization and orientation of developing neurons is essential for the correct wiring of the brain. In pyramidal excitatory neurons, polarization begins with the sprouting of opposite neurites, which later define directed migration and axo-dendritic domains. We here show that endogenous N-cadherin concentrates at one pole of the newborn neuron, from where the first neurite subsequently emerges. Ectopic N-cadherin is sufficient to favour the place of appearance of the first neurite. The Golgi and centrosome move towards this newly formed morphological pole in a second step, which is regulated by PI3K and the actin/microtubule cytoskeleton. Moreover, loss of function experiments in vivo showed that developing neurons with a non-functional N-cadherin misorient their cell axis. These results show that polarization of N-cadherin in the immediate post-mitotic stage is an early and crucial mechanism in neuronal polarity.
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4.41Impact points
Neuronal (bi)polarity as a self-organized process enhanced by growing membrane.
PloS one. 01/2011; 6(9):e24190.
Early in vitro and recent in vivo studies demonstrated that neuronal polarization occurs by the sequential formation of two oppositely located neurites. This early bipolar phenotype is of crucial relevance in brain organization, determining neuronal migration and brain layering. It is currently cons... [more] Early in vitro and recent in vivo studies demonstrated that neuronal polarization occurs by the sequential formation of two oppositely located neurites. This early bipolar phenotype is of crucial relevance in brain organization, determining neuronal migration and brain layering. It is currently considered that the place of formation of the first neurite is dictated by extrinsic cues, through the induction of localized changes in membrane and cytoskeleton dynamics leading to deformation of the cells' curvature followed by the growth of a cylindrical extension (neurite). It is unknown if the appearance of the second neurite at the opposite pole, thus the formation of a bipolar cell axis and capacity to undergo migration, is defined by the growth at the first place, therefore intrinsic, or requires external determinants. We addressed this question by using a mathematical model based on the induction of dynamic changes in one pole of a round cell. The model anticipates that a second area of growth can spontaneously form at the opposite pole. Hence, through mathematical modeling we prove that neuronal bipolar axis of growth can be due to an intrinsic mechanism.
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8.99Impact points
Neuronal polarity: consolidation for growth, growth for consolidation.
The EMBO journal. 03/2009; 28(3):173-4.
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6.14Impact points
Pyramidal neuron polarity axis is defined at the bipolar stage.
Journal of cell science. 02/2008; 121(Pt 2):178-85.
In situ observations of the development of hippocampal and cortical neurons indicate that final axon-dendrite identity is defined at the time of generation of the first two, oppositely positioned, neurites. Quite differently, in vitro studies demonstrated that axonal fate is defined by the stochasti... [more] In situ observations of the development of hippocampal and cortical neurons indicate that final axon-dendrite identity is defined at the time of generation of the first two, oppositely positioned, neurites. Quite differently, in vitro studies demonstrated that axonal fate is defined by the stochastic selection of one of the multiple minor neurites for fast outgrowth. By analyzing the fate of all neurites, starting at the time of emergence from the cell body, we demonstrate that polarity is defined at the bipolar stage, with one of the two first-appearing neurites acquiring axonal fate, irrespective of how many other neurites later form. The first two neurites have, as in vivo, the highest growth potential, as cutting the axon results in the growth of a new axon from the neurite at the opposite pole, and cutting this induces regrowth from the first. This temporal and spatial hierarchical definition of polarized growth, together with the bipolar organization of microtubule dynamics and membrane transport preceding it, is consistent with polarity being initiated by an intrinsic program. In this scenario, molecules required for axon specification would act at one of the first two neurites and extrinsic cues will be required for final commitment of polarity.
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6.14Impact points
Neuronal polarity is regulated by glycogen synthase kinase-3 (GSK-3beta) independently of Akt/PKB serine phosphorylation.
Journal of cell science. 11/2006; 119(Pt 19):3927-34.
An essential step during the development of hippocampal neurons is the polarised outgrowth of a single axon. Recently, it has been suggested that inhibition of glycogen synthase kinase-3beta (GSK-3beta) via Akt/PKB-dependent phosphorylation of Ser9, specifically at the tip of the presumptive axon, i... [more] An essential step during the development of hippocampal neurons is the polarised outgrowth of a single axon. Recently, it has been suggested that inhibition of glycogen synthase kinase-3beta (GSK-3beta) via Akt/PKB-dependent phosphorylation of Ser9, specifically at the tip of the presumptive axon, is required for selective axonal outgrowth. We now report that, by using neurons from double knock-in mice in which Ser9 and Ser21 of the two GSK-3beta isoforms have been replaced by Ala, polarity develops independently of phosphorylation at these sites. Nevertheless, global inhibition of GSK-3beta disturbs polarity development by leading to the formation of multiple axon-like processes in both control and knock-in neurons. This unpolarised outgrowth is accompanied by the symmetric delivery of membrane components to all neurites. Finally, the adenomatous polyposis coli (APC) protein accumulates at the tip of one neurite before and during axon elongation, but global inhibition of GSK-3beta leads to APC protein accumulation in all neurites. We conclude that GSK-3beta inhibition promotes the development of neuronal polarity, but that this is not mediated by Akt/PKB-dependent phosphorylation.
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7.18Impact points
Hippocampal long-term potentiation is supported by presynaptic and postsynaptic tyrosine receptor kinase B-mediated phospholipase Cgamma signaling.
The Journal of neuroscience : the official journal of the Society for Neuroscience. 04/2006; 26(13):3496-504.
Neurotrophins have been shown to play a critical role in activity-dependent synaptic plasticity such as long-term potentiation (LTP) in the hippocampus. Although the role of brain-derived neurotrophic factor (BDNF) and its tyrosine kinase receptor [tyrosine receptor kinase B (TrkB)] is well document... [more] Neurotrophins have been shown to play a critical role in activity-dependent synaptic plasticity such as long-term potentiation (LTP) in the hippocampus. Although the role of brain-derived neurotrophic factor (BDNF) and its tyrosine kinase receptor [tyrosine receptor kinase B (TrkB)] is well documented, it still remains unresolved whether presynaptic or postsynaptic activation of TrkB is involved in the induction of LTP. To address this question, we locally and specifically interfered with a downstream target of the TrkB receptor, phospholipase Cgamma (PLCgamma). We prevented PLCgamma signaling by overexpression of the PLCgamma pleckstrin homology (PH) domain with a Sindbis virus vector. The isolated PH domain has an inhibitory effect and thereby blocks endogenous PLCgamma signaling and consequently also IP3 production. Surprisingly, concurrent presynaptic and postsynaptic blockade of PLCgamma signaling was required to reduce LTP to levels comparable with those in TrkB and BDNF knock-out mice. Blockade of presynaptic or postsynaptic signaling alone did not result in a significant reduction of LTP.
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1.90Impact points
Nucleofection of primary neurons.
Methods in enzymology. 02/2006; 406:374-88.
Efficient gene transfer is an important tool for the study of neuronal function and biology. This has proved difficult and inefficient with traditional transfection strategies, which can also be fairly toxic, whereas viral-mediated gene transfer, although highly efficient, is often time-consuming. T... [more] Efficient gene transfer is an important tool for the study of neuronal function and biology. This has proved difficult and inefficient with traditional transfection strategies, which can also be fairly toxic, whereas viral-mediated gene transfer, although highly efficient, is often time-consuming. The recently developed Amaxa Nucleofector technology, based on electroporation with preset parameters in a cell-type-specific solution, enables direct delivery of DNA, small interfering (si)RNA oligonucleotides and siRNA vectors into the cell nucleus. This strategy results in reproducible, rapid, and efficient transfection of a broad range of cells, including primary neurons. Nucleofected neurons survive for up to 3 weeks and remain functional. We are currently using this transfection method to examine the contribution of Rho GTPase signaling pathways in the establishment of neuronal polarity, neuronal migration, and neurite outgrowth. Here, we describe three protocols to efficiently nucleofect rat cerebellar granule, cortical, and hippocampal neurons.
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9.43Impact points
Neurotrophin secretion from hippocampal neurons evoked by long-term-potentiation-inducing electrical stimulation patterns.
Proceedings of the National Academy of Sciences of the United States of America. 05/2002; 99(9):6386-91.
The neurotrophin (NT) brain-derived neurotrophic factor (BDNF) plays an essential role in the formation of long-term potentiation (LTP). Here, we address whether this modulation by BDNF requires its continuous presence, or whether a local increase in BDNF is necessary during a specific time period o... [more] The neurotrophin (NT) brain-derived neurotrophic factor (BDNF) plays an essential role in the formation of long-term potentiation (LTP). Here, we address whether this modulation by BDNF requires its continuous presence, or whether a local increase in BDNF is necessary during a specific time period of LTP initiation. Using electrical field stimulation of primary cultures of hippocampal neurons, we demonstrate that short high-frequency bursts of stimuli that induce LTP evoke also an instantaneous secretion of BDNF. In contrast, stimuli at low frequencies, inducing long-term depression, do not enhance BDNF secretion, suggesting that BDNF is specifically present, and thus required, at the time of LTP induction. The field-stimulation-mediated BDNF secretion depends on the formation of action potentials and is induced by IP(3)-mediated Ca(2+) release from intracellular stores. Experiments, aimed at determining the sites of NT secretion that use NT6, showed similar patterns of surface labeling by field stimulation to those shown previously by high potassium.
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2.31Impact points
Modification of choline acetyltransferase by integration of green fluorescent protein does not affect enzyme activity and subcellular distribution.
Cell and tissue research. 05/2002; 308(1):1-6.
Choline acetyltransferase (ChAT) is widely used as a marker enzyme to identify cholinergic neurons in the central and peripheral nervous system and to study developmental changes. In order to visualize expression of ChAT directly we have generated a ChAT-green fluorescent protein (GFP) fusion constr... [more] Choline acetyltransferase (ChAT) is widely used as a marker enzyme to identify cholinergic neurons in the central and peripheral nervous system and to study developmental changes. In order to visualize expression of ChAT directly we have generated a ChAT-green fluorescent protein (GFP) fusion construct. Upon transfection of COS-1 cells and cultured rat hippocampal neurons, transgenic enzymatically active ChAT-GFP is expressed and shows intrinsic fluorescence. In COS-1 cells the ChAT-GFP construct revealed a subcellular distribution indistinguishable from wild-type ChAT. In primary neurons the fluorescence was present in the soma and neuritic processes. Hence, this construct will be useful for analyzing the expression and subcellular distribution of ChAT-GFP in cell and tissue culture.
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8.99Impact points
Regulated secretion of neurotrophins by metabotropic glutamate group I (mGluRI) and Trk receptor activation is mediated via phospholipase C signalling pathways.
The EMBO journal. 05/2001; 20(7):1640-50.
Neurotrophins (NTs) play an essential role in modulating activity-dependent neuronal plasticity. In this context, the site and extent of NT secretion are of crucial importance. Here, we demonstrate that the activation of phospolipase C (PLC) and the subsequent mobilization of Ca(2+) from intracellul... [more] Neurotrophins (NTs) play an essential role in modulating activity-dependent neuronal plasticity. In this context, the site and extent of NT secretion are of crucial importance. Here, we demonstrate that the activation of phospolipase C (PLC) and the subsequent mobilization of Ca(2+) from intracellular stores are essential for NT secretion initiated by both Trk and glutamate receptor activation. Mutational analysis of tyrosine residues, highly conserved in the cytoplasmic domain of all Trk receptors, revealed that the activation of PLC-gamma in cultured hippocampal neurons and nnr5 cells is necessary to mobilize Ca(2+) from intracellular stores, the key mechanism for regulated NT secretion. A similar signalling mechanism has been identified for glutamate-mediated NT secretion-which in part depends on the activation of PLC via metabotropic receptors-leading to the mobilization of Ca(2+) from internal stores by inositol trisphosphate. Thus, PLC-mediated signal transduction pathways are the common mechanisms for both Trk- and mGluRI-mediated NT secretion.
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3.57Impact points
Ultrastructural identification of storage compartments and localization of activity-dependent secretion of neurotrophin 6 in hippocampal neurons.
Molecular and cellular neurosciences. 04/2000; 15(3):215-34.
A modulatory role of neurotrophins (NTs) in activity-dependent neuronal plasticity by pre- and postsynaptic mechanisms is now well established. In this context, it is important to identify the storage compartments and to localize the precise site(s) and mechanism of NT secretion in order to deduce t... [more] A modulatory role of neurotrophins (NTs) in activity-dependent neuronal plasticity by pre- and postsynaptic mechanisms is now well established. In this context, it is important to identify the storage compartments and to localize the precise site(s) and mechanism of NT secretion in order to deduce the spatial and temporal availability of NTs. We approached these questions at the ultrastructural level, exploiting the unique property of NT6 to bind tightly to heparan sulfate proteoglycans at the neuronal surface (R. Götz et al., 1994, Nature 372, 266-269), permitting the localization of secretion sites excluding diffusion artifacts. The myc tagging of NT6 permitted glutaraldehyde fixation and hence good preservation of the membrane structure, permitting immunogold labeling of NT6myc at the neuronal surface. NT6myc is preferentially secreted from neurites compared to neuronal cell bodies. In agreement with light-microscopic observations, the ultrastructural localization of NT6myc by postembedding procedures showed a predominant localization in ER-like membrane-confined compartments, partially associated with microtubules.
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Neurotrophins and activity dependent plasticity: Studies on the site and mechanism of the regulated neurotrophin secretion in adenovirally transduced hippocampal primary cultures
04/2000
Degree: summa cum laude
Supervisor: Prof. Hans Thoenen
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7.19Impact points
The role of Pax6 in restricting cell migration between developing cortex and basal ganglia.
Development (Cambridge, England). 01/2000; 126(24):5569-79.
It is not clear to what extent restricted cell migration contributes to patterning of the developing telencephalon, since both restricted and widespread cell migration have been observed. Here, we have analysed dorso-ventral cell migration in the telencephalon of Pax6 mutant mice (Small Eye). The tr... [more] It is not clear to what extent restricted cell migration contributes to patterning of the developing telencephalon, since both restricted and widespread cell migration have been observed. Here, we have analysed dorso-ventral cell migration in the telencephalon of Pax6 mutant mice (Small Eye). The transcription factor Pax6 is expressed in the dorsal telencephalon, the cerebral cortex. Focal injections of adenoviral vectors containing the green fluorescent protein were used to follow and quantify cell movements between two adjacent regions in the developing telencephalon, the cerebral cortex and the ganglionic eminence (the prospective basal ganglia). The analysis in wild-type mice confirmed that the cortico-striatal boundary acts as a semipermeable filter and allows a proportion of cells from the ganglionic eminence to invade the cortex, but not vice versa. Ventro-dorsal cell migration was strongly enhanced in the Pax6 mutant. An essential function of Pax6 in the regionalisation of the telencephalon is then to limit the invasion of the cortex by cells originating in the ganglionic eminence. Cortical cells, however, remain confined to the cortex in the Pax6 mutant. Thus, dorsal and ventral cells are restricted to their respective territories by distinct mechanisms.
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1.85Impact points
Are there differences between the secretion characteristics of NGF and BDNF? Implications for the modulatory role of neurotrophins in activity-dependent neuronal plasticity.
Microscopy research and technique. 01/1999; 45(4-5):262-75.
In previous experiments the activity-dependent secretion of nerve growth factor (NGF) from native hippocampal slices and from NGF-cDNA transfected hippocampal neurons showed unusual characteristics [Blochl and Thoenen (1995) Eur J Neurosci 7:1220-1228; (1996) Mol Cell Neurosci 7:173-190]. In both hi... [more] In previous experiments the activity-dependent secretion of nerve growth factor (NGF) from native hippocampal slices and from NGF-cDNA transfected hippocampal neurons showed unusual characteristics [Blochl and Thoenen (1995) Eur J Neurosci 7:1220-1228; (1996) Mol Cell Neurosci 7:173-190]. In both hippocampal slices and cultured hippocampal neurons the activity-dependent secretion proved to be independent of extracellular calcium, but dependent on the release of calcium from intracellular stores. Under different experimental conditions, Goodman et al. [(1996) Mol Cell Neurosci 7:222-238] reported that the high potassium-mediated secretion of brain-derived neurotrophic factor (BDNF) from hippocampal cultures was dependent on extracellular calcium. Mowla et al. [(1997) Proc 27th Annu Meet Soc Neurosci New Orleans 875.10] reported on even further-reaching differences between NGF and BDNF secretion, namely, that in hippocampal neurons and in pituitary cell lines NGF was secreted exclusively according to the constitutive pathway, whereas BDNF was exclusively sorted according to the activity-dependent regulated pathway. In view of the crucial importance of such potential differences between the processing, sorting, and secretory mechanisms of different neurotrophins for their modulatory roles in activity-dependent neuronal plasticity, a thorough analysis under comparable experimental conditions was mandatory. We demonstrate that in native hippocampal slices and adenoviral-transduced hippocampal neurons there are no differences between NGF and BDNF with respect to the subcellular distribution and mechanism of secretion; that the activity-dependent secretion of both NGF and BDNF is dependent on intact intracellular calcium stores; and that the differences between our own observations and those of Goodman et al. (ibid.) regarding the dependence on extracellular calcium do not reflect differences between NGF and BDNF sorting and secretion, but reflect the differing experimental conditions used.
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6.14Impact points
Myr 7 is a novel myosin IX-RhoGAP expressed in rat brain.
Journal of cell science. 01/1999; 111 ( Pt 24):3597-608.
Rho family GTPases are important regulators of neuronal morphology, but the proteins directly controlling their activity in neurons are still poorly defined. We report the identification of myr 7, a novel unconventional myosin IX-RhoGAP expressed in rat brain. Myr 7 is a multidomain protein related ... [more] Rho family GTPases are important regulators of neuronal morphology, but the proteins directly controlling their activity in neurons are still poorly defined. We report the identification of myr 7, a novel unconventional myosin IX-RhoGAP expressed in rat brain. Myr 7 is a multidomain protein related to myr 5, the first class IX myosin to be characterized. It exhibits a myosin head domain with an N-terminal extension and a large insertion at loop 2, an actin contact site and regulator of myosin ATPase rate. The myosin head domain is followed by a neck domain consisting of six unevenly spaced consecutive IQ motifs representing light chain binding sites. The tail domain contains a C6H2-zinc binding motif and a region that specifically stimulates the GTPase-activity of Rho followed by a short stretch predicted to adopt a coiled-coil structure. Five alternatively spliced regions, one in the 5'-noncoding region, two in the myosin head and two in the tail domain, were noted. Analysis of myr 7 and myr 5 expression in different tissues revealed that myr 7 is expressed at high levels in developing and adult brain tissue whereas myr 5 is expressed only at moderate levels in embryonic brain tissue and at even further reduced levels in adult brain tissue. Myr 5 is, however, highly expressed in lung, liver, spleen and testis. Myr 7 is expressed in all brain regions and is localized in the cytoplasm of cell bodies, dendrites and axons. Myr 5 exhibits an overlapping, but not identical cellular distribution. Finally, a myr 7 fusion protein encompassing the GAP domain specifically activates the GTPase-activity of Rho in vitro, and overexpression of myr 7 in HtTA1-HeLa cells leads to inactivation of Rho in vivo. These results are compatible with a role for myr 7 (and myr 5) in regulating Rho activity in neurons and hence in regulating neuronal morphology and function.
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Regulated secretion of neurotrophins by metabotropic glutamate group I (mGluRI) and Trk receptor activation is mediated via phospholipase C signalling pathways
Neurotrophins (NTs) play an essential role in modulating activity-dependent neuronal plasticity. In this context, the site and extent of NT secretion are of crucial importance. Here, we demonstrate that the activation of phospolipase C (PLC) and the subsequent mobilization of Ca2+ from intracellular... [more] Neurotrophins (NTs) play an essential role in modulating activity-dependent neuronal plasticity. In this context, the site and extent of NT secretion are of crucial importance. Here, we demonstrate that the activation of phospolipase C (PLC) and the subsequent mobilization of Ca2+ from intracellular stores are essential for NT secretion initiated by both Trk and glutamate receptor activation. Mutational analysis of tyrosine residues, highly conserved in the cytoplasmic domain of all Trk receptors, revealed that the activation of PLC-γ in cultured hippocampal neurons and nnr5 cells is necessary to mobilize Ca2+ from intracellular stores, the key mechanism for regulated NT secretion. A similar signalling mechanism has been identified for glutamate-mediated NT secretion—which in part depends on the activation of PLC via metabotropic receptors—leading to the mobilization of Ca2+ from internal stores by inositol trisphosphate. Thus, PLC-mediated signal transduction pathways are the common mechanisms for both Trk- and mGluRI-mediated NT secretion.
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Neurotrophine und aktivitätsabhängige synaptische Plastizität [Elektronische Ressource] : Untersuchungen zum Ort und Mechanismus der regulierten Neurotrophin-Freisetzung in adenoviral transduzierten hippokampalen Primärkulturen /
Tübingen, Univ., Diss., 2000. Computerdatei im Fernzugriff.
Following (2)
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Tim Hucho
Universitätsklinikum Köln -
Froylan Calderon de Anda
Massachusetts Institute of Technology
Topics (2)
