Synapses are specialized sites of cell-cell contact that mediate communication between neurons in the nervous system. Much remains to be discovered about the molecular mechanisms that underlie formation of these critical structures in the mammalian central nervous system. While recent advances have contributed to our understanding of excitatory synapse formation, the processes that mediate inhibitory synapse formation remain poorly defined. In addition, it is hypothesized that aberrant synapse formation and function contributes to neurological disorders such as mental retardation, autism spectrum disorders and epilepsy. To appreciate how synapse dysfunction contributes to these widespread neurological impairments, it is important to first understand how synapses are formed, maintained, and function in the non-pathological state. To this end, we developed a novel, forward genetic RNA interference (RNAi)-based screen in cultured hippocampal neurons that has identified new molecules required for synapse formation. Using this technique, we discovered that RNAi-mediated knockdown of a class 4 Semaphorin, Sema4D, led to a decrease in the density of inhibitory synapses without an apparent effect on excitatory synapse formation. Thus, Sema4D is one of only a few molecules identified thus far that preferentially regulates inhibitory synapse formation. Further, Sema4D appears to be playing a specific role in assembling the postsynaptic specialization at inhibitory synapses. Therefore, understanding the mechanism of action of Sema4D in this process promises to yield key insights into the assembly of inhibitory synapses in the mammalian central nervous system.
Numerous studies now point to defects in synapse formation as a possible cause for neurological disorders such as autism, mental retardation, and epilepsy. To appreciate how aberrant synapse formation contributes to these widespread neurological impairments, it is important to first understand how synapses are formed, maintained, and function in the non-pathological state. Thus, in-depth study of the mechanism of action of Sema4D in synapse formation as outlined in this proposal has the potential to yield important insights into the underlying cause of some of these disorders.
|Raissi, Aram J; Scangarello, Frank A; Hulce, Kaitlin R et al. (2014) Enhanced potency of the metalloprotease inhibitor TAPI-2 by multivalent display. Bioorg Med Chem Lett 24:2002-7|
|Ghiretti, Amy E; Paradis, Suzanne (2014) Molecular mechanisms of activity-dependent changes in dendritic morphology: role of RGK proteins. Trends Neurosci 37:399-407|
|Ghiretti, Amy E; Moore, Anna R; Brenner, Rebecca G et al. (2014) Rem2 is an activity-dependent negative regulator of dendritic complexity in vivo. J Neurosci 34:392-407|
|Raissi, Aram J; Staudenmaier, Emily K; David, Serena et al. (2013) Sema4D localizes to synapses and regulates GABAergic synapse development as a membrane-bound molecule in the mammalian hippocampus. Mol Cell Neurosci 57:23-32|
|Moore, Anna R; Ghiretti, Amy E; Paradis, Suzanne (2013) A loss-of-function analysis reveals that endogenous Rem2 promotes functional glutamatergic synapse formation and restricts dendritic complexity. PLoS One 8:e74751|
|Ghiretti, Amy E; Kenny, Katelyn; Marr 2nd, Michael T et al. (2013) CaMKII-dependent phosphorylation of the GTPase Rem2 is required to restrict dendritic complexity. J Neurosci 33:6504-15|
|Kuzirian, Marissa S; Moore, Anna R; Staudenmaier, Emily K et al. (2013) The class 4 semaphorin Sema4D promotes the rapid assembly of GABAergic synapses in rodent hippocampus. J Neurosci 33:8961-73|
|Ghiretti, Amy E; Paradis, Suzanne (2011) The GTPase Rem2 regulates synapse development and dendritic morphology. Dev Neurobiol 71:374-89|
|Kuzirian, Marissa S; Paradis, Suzanne (2011) Emerging themes in GABAergic synapse development. Prog Neurobiol 95:68-87|