The Cdc42-selective GAP Rich regulates postsynaptic development and retrograde BMP transsynaptic signaling

Abstract

Retrograde bone morphogenetic protein signaling mediated by the Glass bottom boat (Gbb) ligand modulates structural and functional synaptogenesis at the Drosophila melanogaster neuromuscular junction However, the molecular mechanisms regulating post synaptic Gbb release are poorly understood In this study, we show that Drosophila Rich (dRich), a conserved Cdc42-selective guanosine triphosphatase activating protein (GAP), inhibits the Cdc42-Wsp pathway to stimulate postsynaptic Gbb release Loss of dRich causes synaptic undergrowth and strongly impairs neurotransmitter release These presynaptic defects are rescued by targeted postsynaptic expression of wild type dRich but not a GAP-deficient mutant dRich inhibits the post synaptic localization of the Cdc42 effector Wsp (Drosophila orthologue of mammalian Wiskott Aldrich syndrome protein, WASp), and manifestation of synaptogenesis defects in drich mutants requires Wsp signaling In addition, dRich regulates postsynaptic organization independently of Cdc42 Importantly, dRich increases Gbb release and elevates presynaptic phosphorylated Mad levels We propose that dRich coordinates the Gbb dependent modulation of synaptic growth and function with postsynaptic development