Glutamate is the primary excitatory neurotransmitter in the nervous system, and formation of glutamatergic synapses is therefore a critical step in establishing neural circuits. Synaptogenesis defects cause many crippling neurological disabilities, including motor ataxias, autism spectrum disorders and cognitive deficits. The aim of this long-term, ongoing research program is to use the power of the Drosophila genetic system to reveal molecular mechanisms of glutamatergic synaptogenesis, and thereby to provide a basis for the understanding and treatment of both inherited and teratogenic synaptic development defects. This grant has been funded for more than a decade to systematically screen the Drosophila genome for mutations that perturb functional synaptic development;30+ essential "synaptogenic genes" have been identified. During the current funding cycle, we have cloned and characterized several of these genes to generate novel insights into synaptogenic mechanisms. This continuation proposal continues this strategy with the large number of remaining genes. A primary focus will be on roles of synaptic extracellular matrix (ECM) and ECM receptors (synaptic integrins). One gene identified in our screen, mind the gap (mtg), encodes a presynaptic protein essential for formation of the specialized synaptic cleft ECM and required to induce postsynaptic differentiation. In related studies funded by this grant, we have similarly shown that 3 classes of position specific (PS) integrins act as presynaptic (1) and postsynaptic (2) ECM receptors critical for multiple aspects of synaptogenesis. Our hypothesis, therefore, is that ECM-based signaling is critical for synaptogenesis and that integrins are one key receptor class mediating this signaling. This proposal uses mtg and PS integrin mutants to test this hypothesis by eliminating ECM signals and ECM receptors, respectively. We will assay mechanisms by which MTG and PS integrins regulate synaptic development, particularly in the postsynaptic domain. We will determine the site and timing of MTG and PS integrin requirements by spatial and temporal removal of both gene classes. We will focus particularly on genetic interactions between MTG, PS integrins and the downstream dPix-dPak-Dock-DLG signaling pathway. These aims will include confocal and electron microscopy imaging, synaptic electrophysiological recording and extensive molecular genetic studies. We will continue screens for synaptogenesis mutants.