The Specific α-Neurexin Interactor Calsyntenin-3 Promotes Excitatory and Inhibitory Synapse Development

Abstract

Perturbations of cell surface synapse-organizing proteins, particularly alpha-neurexins, contribute to neurodevelopmental and psychiatric disorders. From an unbiased screen, we identify calsyntenin-3 (alcadein-beta) as a synapse-organizing protein unique in binding and recruiting alpha-neurexins, but not beta-neurexins. Calsyntenin-3 is present in many pyramidal neurons throughout cortex and hippocampus but is most highly expressed in interneurons. The transmembrane form of calsyntenin-3 can trigger excitatory and inhibitory presynapse differentiation in contacting axons. However, calsyntenin-3-shed ectodomain, which represents about half the calsyntenin-3 pool in brain, suppresses the ability of multiple alpha-neurexin partners including neuroligin 2 and LRRTM2 to induce presynapse differentiation. Cistn3(-/-) mice show reductions in excitatory and inhibitory synapse density by confocal and electron microscopy and corresponding deficits in synaptic transmission. These results identify calsyntenin-3 as an alpha-neurexin-specific binding partner required for normal functional GABAergic and glutamatergic synapse development.