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Scott A Wilke,
Benjamin J Hall,
Joseph K Antonios,
Laura A Denardo,
Stefanie Otto,
Bo Yuan,
Fading Chen,
Elissa M Robbins,
Katie Tiglio, Megan E Williams,
Zilong Qiu,
Thomas Biederer,
Anirvan Ghosh
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ABSTRACT: The assembly of neural circuits requires the concerted action of both genetically determined and activity-dependent mechanisms. Calcium-regulated transcription may link these processes, but the influence of specific transcription factors on the differentiation of synapse-specific properties is poorly understood. Here we characterize the influence of NeuroD2, a calcium-dependent transcription factor, in regulating the structural and functional maturation of the hippocampal mossy fiber (MF) synapse.
Using NeuroD2 null mice and in vivo lentivirus-mediated gene knockdown, we demonstrate a critical role for NeuroD2 in the formation of CA3 dendritic spines receiving MF inputs. We also use electrophysiological recordings from CA3 neurons while stimulating MF axons to show that NeuroD2 regulates the differentiation of functional properties at the MF synapse. Finally, we find that NeuroD2 regulates PSD95 expression in hippocampal neurons and that PSD95 loss of function in vivo reproduces CA3 neuron spine defects observed in NeuroD2 null mice.
These experiments identify NeuroD2 as a key transcription factor that regulates the structural and functional differentiation of MF synapses in vivo.
Neural Development 02/2012; 7:9. · 3.70 Impact Factor
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Megan E Williams,
Scott A Wilke,
Anthony Daggett,
Elizabeth Davis,
Stefanie Otto,
Deepak Ravi,
Beth Ripley,
Eric A Bushong,
Mark H Ellisman,
Gerd Klein,
Anirvan Ghosh
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ABSTRACT: Our understanding of mechanisms that regulate the differentiation of specific classes of synapses is limited. Here, we investigate the formation of synapses between hippocampal dentate gyrus (DG) neurons and their target CA3 neurons and find that DG neurons preferentially form synapses with CA3 rather than DG or CA1 neurons in culture, suggesting that specific interactions between DG and CA3 neurons drive synapse formation. Cadherin-9 is expressed selectively in DG and CA3 neurons, and downregulation of cadherin-9 in CA3 neurons leads to a selective decrease in the number and size of DG synapses onto CA3 neurons. In addition, loss of cadherin-9 from DG or CA3 neurons in vivo leads to striking defects in the formation and differentiation of the DG-CA3 mossy fiber synapse. These observations indicate that cadherin-9 bidirectionally regulates DG-CA3 synapse development and highlight the critical role of differentially expressed molecular cues in establishing specific connections in the mammalian brain.
Neuron 08/2011; 71(4):640-55. · 14.74 Impact Factor
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ABSTRACT: The establishment of neuronal circuits relies on the stabilization of functionally appropriate connections and the elimination of inappropriate ones. Here we report that postsynaptic AMPA receptors play a critical role in regulating the stability of glutamatergic synapses. Removal of surface AMPA receptors leads to a decrease in the number and stability of excitatory presynaptic inputs, whereas overexpression increases synapse number and stability. Furthermore, overexpression of AMPA receptors along with Neuroligin-1 in 293T cells is sufficient to stabilize presynaptic inputs from cortical neurons onto heterologous cells. The stabilization of presynaptic inputs by AMPA receptors is not dependent on receptor-mediated current and instead relies on structural interactions mediated by the N-terminal domain of the glutamate receptor 2 (GluR2) subunit. These observations indicate that transsynaptic signaling mediated by the extracellular domain of GluR2 regulates the stability of presynaptic terminals.
Proceedings of the National Academy of Sciences 01/2011; 108(1):367-72. · 9.68 Impact Factor
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ABSTRACT: The function of the brain depends on highly specific patterns of connections between populations of neurons. The establishment of these connections requires the targeting of axons and dendrites to defined zones or laminae, the recognition of individual target cells, the formation of synapses on particular regions of the dendritic tree, and the differentiation of pre- and postsynaptic specializations. Recent studies provide compelling evidence that transmembrane adhesion proteins of the immunoglobulin, cadherin, and leucine-rich repeat protein families, as well as secreted proteins such as semaphorins and FGFs, regulate distinct aspects of neuronal connectivity. These observations suggest that the coordinated actions of a number of molecular signals contribute to the specification and differentiation of synaptic connections in the developing brain.
Neuron 10/2010; 68(1):9-18. · 14.74 Impact Factor
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ABSTRACT: Acyl-CoA-binding protein (ACBP) functions both intracellularly as part of fatty acid metabolism and extracellularly as diazepam binding inhibitor, the precursor of endozepine peptides. Two of these peptides, ODN and TTN, bind to the GABA(A) receptor and modulate its sensitivity to gamma-aminobutyric acid (GABA). We have found that depolarization of mouse primary astrocytes induces the rapid release and processing of ACBP to the active peptides. We previously showed that ODN can trigger the rapid sporulation of the social amoeba Dictyostelium. Using this bioassay, we now show that astrocytes release the endozepine peptides within 10 min of exposure to the steroids cortisol, pregnenolone, pregnenolone sulfate, or progesterone. ACBP lacks a signal sequence for secretion through the endoplasmic reticulum/Golgi pathway and its secretion is not affected by addition of brefeldin A, a well known inhibitor of the classical secretion pathway, suggesting that it follows an unconventional pathway for secretion. Moreover, induction of autophagy by addition of rapamycin also resulted in rapid release of ACBP indicating that this protein uses components of the autophagy pathway for secretion. Following secretion, ACBP is proteolytically cleaved to the active neuropeptides by protease activity on the surface of astrocytes. Neurosteroids, such as pregnenolone sulfate, were previously shown to modulate the excitatory/inhibitory balance in brain through increased release of glutamate and decreased release of GABA. These effects of steroids in neurons will be reinforced by the release of endozepines from astrocytes shown here, and suggest an orchestrated astrocyte-neuron cross-talk that can affect a broad spectrum of behavioral functions.
Journal of Biological Chemistry 05/2010; 285(28):21359-65. · 4.77 Impact Factor
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ABSTRACT: Peptidyl-prolyl cis-trans isomerases are a group of cytosolic enzymes initially characterized by their ability to catalyze the cis-trans isomerization of peptidyl-prolyl bonds. This represents a significant event for protein folding because cis-proline introduces critical bends within the protein conformation. FK506-binding proteins (FKBPs) represent one of the three families of enzymes sharing peptidyl-prolyl cis-trans isomerase activity. Inhibitors of FKBP12, in particular, have potent neurotrophic properties both in vivo and in vitro. Here, we describe a fragment-based unbiased nuclear magnetic resonance drug discovery approach for the identification of novel classes of chemical inhibitors against FKBP12. Compared to FK506, the fragment-based FKBP12 inhibitors developed herein possess significant advantages as drug candidates.
Journal of Medicinal Chemistry 01/2008; 50(26):6607-17. · 5.25 Impact Factor
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ABSTRACT: In addition to their role as chemorepellent netrin-1 receptors, UNC5 proteins may mediate cell death because they induce apoptosis in cultured cells. To test this in vivo, we generated Unc5a (formerly Unc5h1) knockout mice and found that this deletion decreased apoptosis and increased the number of neurons in the spinal cord. In contrast, loss of netrin-1 (Ntn1) did not affect the amount of apoptosis, suggesting that NTN1 is not required for neuronal apoptosis in vivo.
Nature Neuroscience 09/2006; 9(8):996-8. · 15.53 Impact Factor
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ABSTRACT: Netrin-1 is a bifunctional guidance cue that directs migrating neurons and axons based on specific receptors expressed on the cell surface. Attraction occurs through the receptor Deleted in Colorectal Cancer (DCC) and repulsion occurs through a receptor complex of DCC and UNC5H, the vertebrate homolog to Caenorhabditis elegans UNC-5, but how the specific surface expression of these receptors is achieved remains unknown. Here, we demonstrate that surface expression of UNC5H1 is regulated in neurons by protein interacting with C kinase-1 (PICK1) and protein kinase C (PKC), and show that one mechanism by which cells control their response to netrin-1 is by changing the surface availability of receptors. We identified PICK1 as a binding partner for UNC5H1 using the yeast two-hybrid system and found that the extreme three C-terminal amino acids of UNC5H1 interact with the PSD-95/Dlg/ZO-1 (PDZ) domain of PICK1. Coexpression of UNC5H1 and PICK1 in heterologous cells results in the recruitment of PICK1 to UNC5H1 clusters. Endogenous UNC5H1 and PICK1 coimmunoprecipitate from extracts of cultured hippocampal neurons and P4 cortices, and immunohistochemistry shows that UNC5H1, PICK1, and PKC are all present in growth cones. PKC activation induces the formation of UNC5H1/PICK1/PKC complexes and leads to the specific removal of UNC5H1, but not DCC, from the surface of neurons and growth cones via a PICK1/PKC-dependent mechanism. Lastly, we demonstrate that activating PKC, which decreases surface expression of UNC5H1, inhibits netrin-1-dependent collapse of hippocampal growth cones. Together, our results suggest that by regulating the surface expression of UNC5Hs, an axon can modulate its repellent response to netrin-1.
Journal of Neuroscience 01/2004; 23(36):11279-88. · 7.11 Impact Factor
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ABSTRACT: The UNC5Hs are axon guidance receptors that mediate netrin-1-dependent chemorepulsion, and dependence receptors that mediate netrin-1-independent apoptosis. Here, we report an interaction between UNC5H1 and NRAGE. Our experiments show that this interaction is responsible for apoptosis induced by UNC5H1, and this level of apoptosis is greater than the amount induced by either UNC5H2 or UNC5H3. We mapped the NRAGE binding domain of UNC5H1 to its ZU-5 domain and show that this region, in addition to an adjacent PEST sequence, is required for UNC5H1-mediated apoptosis. Chimeric UNC5H2 and UNC5H3 receptors, containing the NRAGE binding domain and PEST sequence of UNC5H1, bind NRAGE and cause increased levels of apoptosis. UNC5H1 expression does not induce apoptosis in differentiated PC12 cells, which down-regulate NRAGE, but induces apoptosis in native PC12 cells that endogenously express high levels of NRAGE and in differentiated PC12 cells when NRAGE is overexpressed. Together, these results demonstrate a mechanism for UNC5H1-mediated apoptosis that requires an interaction with the MAGE protein NRAGE.
Journal of Biological Chemistry 06/2003; 278(19):17483-90. · 4.77 Impact Factor
