UNC-43/CaMKII-triggered anterograde signals recruit GABA A Rs to mediate inhibitory synaptic transmission and plasticity at C. elegans NMJs.

Disturbed inhibitory synaptic transmission has functional impacts on neurodevelopmental and psychiatric disorders. An essential mechanism for modulating inhibitory synaptic transmission is alteration of the postsynaptic abundance of GABA A Rs, which are stabilized by postsynaptic scaffold proteins and recruited by presynaptic signals. However, how GABAergic neurons trigger signals to transsynaptically recruit GABA A Rs remains elusive. Here, we show that UNC-43/CaMKII functions at GABAergic neurons to recruit GABA A Rs and modulate inhibitory synaptic transmission at C. elegans neuromuscular junctions. We demonstrate that UNC-43 promotes presynaptic MADD-4B/Punctin secretion and NRX-1α/Neurexin surface delivery. Together, MADD-4B and NRX-1α recruit postsynaptic NLG-1/Neuroligin and stabilize GABA A Rs. Further, the excitation of GABAergic neurons potentiates the recruitment of NLG-1-stabilized-GABA A Rs, which depends on UNC-43, MADD-4B, and NRX-1. These data all support that UNC-43 triggers MADD-4B and NRX-1α, which act as anterograde signals to recruit postsynaptic GABA A Rs. Thus, our findings elucidate a mechanism for pre- and postsynaptic communication and inhibitory synaptic transmission and plasticity.