gamma-Protocadherins Negatively Regulate Inhibitory Presynaptic Differentiation Induced by Neuroligin-2
The 22 g-Protocadherins (g-Pcdhs) are a family of cell-adhesion molecules expressed throughout the brain that play critical roles in synaptogenesis, neuronal survival, and dendrite arborization. While the g-Pcdhs exhibit homophilic trans-interactions and promiscuous cis-interactions with each other, these molecules also share cis-interactions with other families of synaptic proteins. Recently, the Weiner lab demonstrated a novel cis-interaction between the g-Pcdhs and another neuronal adhesion molecule called neuroligin-1 (NLG1), a postsynaptic adhesion molecule important for the maturation of excitatory synapses (Molumby, et al., 2017). It was shown that the g-Pcdhs could inhibit NLG1’s ability to induce presynaptic differentiation in an “artificial synapse assay” (Molumby, et al., 2017). Although Molumby, et al. clearly demonstrated a mechanism by which the g-Pcdhs regulate excitatory presynaptic differentiation, it was unknown whether the g-Pcdhs could affect inhibitory synapses in a similar manner. Here, I provide evidence that the g-Pcdhs can also negatively regulate inhibitory presynaptic differentiation. Using in vitro and in vivo co-immunoprecipitation assays, I show that the g-Pcdhs interact with neuroligin-2 (NLG2), a neuroligin molecule localized to inhibitory synapses with similar functions as NLG1. In two variations of the artificial synapse assay, I demonstrate that the g-Pcdhs can, when co-expressed with NLG2 in COS7 cells, reduce NLG2’s ability to promote clustering of synaptic proteins in contacting axons. Together, my data indicate that a cis-interaction between the g-Pcdhs and NLG2 can negatively regulate inhibitory presynaptic differentiation.