Phosphorylation of NLGN4X Regulates Spinogenesis and Synaptic Function

Neuroligins (NLGNs) are a family of postsynaptic adhesion molecules that bind to their presynaptic partners, neurexins, facilitating the formation and maintenance of synapses. In humans, there are five genes encoding NLGNs (<i>NLGN1-3</i>, <i>NLGN4X</i>, and <i>NLGN4Y</i>), with <i>NLGN1-3</i> having highly conserved counterparts in rodents, allowing these genes to be studied with high confidence of translational validity in mouse models. Human NLGN4X and 4Y were often assumed to serve similar functions because they share a 97% sequence homology, whereas mouse NLGN4-like is quite divergent. Many NLGN-mediated synaptic effects are modulated through post-translation modifications, which exert temporal and spatial control. In this report, we characterize a conserved phosphorylation site, serine 712, on NLGN4X and 4Y. Despite serine 712 being located in a highly conserved region between NLGN4X and 4Y, we observed kinase specificity. PKA exclusively phosphorylates NLGN4X S712, whereas Cdk5 phosphorylates S712 on both NLGN4X and 4Y. NLGN4X S712 phosphorylation regulated spine density, with phosphorylation reducing mature mushroom spines and unphosphorylated S712 increasing spines and enhancing miniature excitatory postsynaptic current frequency.