Abstract
The development of the nervous system involves an interconnected series of events, including neuronal ditl'erentiation, neuronal migration, axon guidance, and synapse fonnation. Synapse assembly and stabilization requires the precise and coordinated action of numerous proteins. Recent research has identified many novel synaptogenic proteins, including several class four semaphoriri members. Semaphorin 48 and Semaphorin 40 were identified through an RNA interference-based assay in primary culture to be involved in the development of GA8Aergic and/or glutamatergic synapses in the rat hippocampus. Semaphorin 48 is involved in both types of synapse fonnation; Scmaphorin 40 is involved in only GA8Aergic synapse development. The current study considered the role of another class four scmaphorin, Semaphorin 4A, in mammalian central nervous system synaptogenesis. Semaphorin 4A expression was knocked down via RNAi in primary cultured rat hippocampal neurons, and synapses made onto the postsynaptic cell were quantified using immunostaining and confocal microscopy. Two different shRNAs known to knock down Semaphorin 4A caused significant decreases in both glutamatergic and GABAergic synaptic density. However, one shRNA also negatively affected cell health. These results indicate a possible role for Semaphorin 4A in both glutamatergic and GA8Aergie synapse development.