Exocyst-positive organelle (EXPO) is a double-membrane organelle mediating unconventional protein secretion in plants. The Arabidopsis exocyst subunit AtExo70E2 is essential for the recruitment of other exocyst subunits to EXPO and plays a key role in EXPO formation in both plant and animal cells.

Normal brain functions depend on the balanced development of excitatory and inhibitory synapses. Our knowledge of the molecular mechanisms underlying inhibitory synapse formation is limited. Neuroligin-2 (NL2), a transmembrane protein at inhibitory postsynaptic sites, is capable of initiating inhibitory synapse formation. In an effort to search for NL2 binding proteins and the downstream mechanisms responsible for inhibitory synapse development, we identify LHFPL4/GARLH4 as a major NL2 binding partner that is specifically enriched at inhibitory postsynaptic sites. LHFPL4/GARLH4 and NL2 regulate the protein levels and synaptic clustering of each other in the cerebellum. Lhfpl4/Garlh4 mice display profound impairment of inhibitory synapse formation as well as prominent motor behavioral deficits and premature death. Our findings highlight the essential role of LHFPL4/GARLH4 in brain functions by regulating inhibitory synapse formation as a major NL2 binding partner.