Integrins regulate DLG/FAS2 via a CaM kinase II-dependent pathway to mediate synapse elaboration and stabilization during postembryonic development

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Abstract
Calcium/calmodulin dependent kinase II (CaMKII), PDZ-domain scaffolding protein Discs-large (DLG), immunoglobin superfamily cell adhesion molecule Fasciclin 2 (FAS2) and the position specific (PS) integrin receptors, including βPS and its alpha partners (αPS1, αPS2, αPS3/αVolado), are all known to regulate the postembryonic development of synaptic terminal arborization at the Drosophila neuromuscular junction (NMJ). Recent work has shown that DLG and FAS2 function together to modulate activity-dependent synaptic development and that this role is regulated by activation of CaMKII. We show that PS integrins function upstream of CaMKII in the development of synaptic architecture at the NMJ. βPS integrin physically associates with the synaptic complex anchored by the DLG scaffolding protein, which contains CaMKII and FAS2. We demonstrate an alteration of the FAS2 molecular cascade in integrin regulatory mutants, as a result of CaMKII/integrin interactions. Regulatory βPS integrin mutations increase the expression and synaptic localization of FAS2. Synaptic structural defects in βPS integrin mutants are rescued by transgenic overexpression of CaMKII (proximal in pathway) or genetic reduction of FAS2 (distal in pathway). These studies demonstrate that βPS integrins act through CaMKII activation to control the localization of synaptic proteins involved in the development of NMJ synaptic morphology.