Abstract
Synapse formation is a critical process in our brain which determines how proper circuit formation and function is regulated. Investigating the role of synaptic molecules involved in both types of synapse formation is crucial for establishing a signaling model for how synapses are formed. The Paradis lab has previously established that Class 4 Semaphorin ligands and their transmembrane receptors, the Plexin-Bs, are involved in regulating both inhibitory and excitatory synapse formation. Our lab has previously demonstrated that Sema4D-Fc triggers an increase in GABAergic synapse density in a PlexinB1-dependent manner, indicating that Plexin-B1 may help regulate inhibitory synapse formation. Here we provide results which demonstrate that receptor Plexin-B2 and not Plexin-B1 is in fact required for sufficient inhibitory synapse density in the mammalian hippocampus. This paper also provides results which examine the ligand Sema4A’s role during synapse formation utilizing a Sema4Aflx/flx transgenic mouse line. Previous data obtained in dissociated hippocampal neurons showed that when Sema4A was knocked out using RNAi both glutamatergic and GABAergic synapse density levels decreased. Our results reaffirm Sema4A’s requirement during inhibitory synapse formation by using organotypic slices to quantify inhibitory synapse density when Sema4A has been knocked out (using Cre recombinase) in the hippocampus. Our results also establish the Sema4Aflx/flx transgenic mouse line as a reliable tool for further studying Sema4A’s signaling mechanisms during synapse formation.