RESUMO
Dscam2 is a cell surface protein required for neuronal development in Drosophila; it can promote neural wiring through homophilic recognition that leads to either adhesion or repulsion between neurites. Here, we report that Dscam2 also plays a post-developmental role in suppressing synaptic strength. This function is dependent on one of two distinct extracellular isoforms of the protein and is autonomous to motor neurons. We link the PI3K enhancer, Centaurin gamma 1A, to the Dscam2-dependent regulation of synaptic strength and show that changes in phosphoinositide levels correlate with changes in endosomal compartments that have previously been associated with synaptic strength. Using transmission electron microscopy, we find an increase in synaptic vesicles at Dscam2 mutant active zones, providing a rationale for the increase in synaptic strength. Our study provides the first evidence that Dscam2 can regulate synaptic physiology and highlights how diverse roles of alternative protein isoforms can contribute to unique aspects of brain development and function.
Assuntos
Proteínas de Drosophila/metabolismo , Drosophila/metabolismo , Endossomos/metabolismo , Proteínas Ativadoras de GTPase/metabolismo , Larva/crescimento & desenvolvimento , Neurônios Motores/metabolismo , Moléculas de Adesão de Célula Nervosa/metabolismo , Neurogênese/genética , Fosfatidilinositol 3-Quinases/metabolismo , Animais , Animais Geneticamente Modificados , Drosophila/crescimento & desenvolvimento , Proteínas de Drosophila/genética , Endossomos/genética , Endossomos/ultraestrutura , Imuno-Histoquímica , Larva/genética , Larva/fisiologia , Larva/ultraestrutura , Microscopia Eletrônica de Transmissão , Neurônios Motores/fisiologia , Mutação , Moléculas de Adesão de Célula Nervosa/genética , Junção Neuromuscular/citologia , Junção Neuromuscular/genética , Sistema Nervoso Periférico/metabolismo , Fosfatidilinositóis/metabolismo , Inibidores de Fosfoinositídeo-3 Quinase/farmacologia , Isoformas de Proteínas/metabolismo , Transmissão Sináptica/genética , Transmissão Sináptica/fisiologiaRESUMO
How the brain makes trillions of synaptic connections using a genome of only 20,000 genes is a major question in modern neuroscience. Alternative splicing is one mechanism that can increase the number of proteins produced by each gene, but its role in regulating synapse formation is poorly understood. In Drosophila, photoreceptors form a synapse with multiple postsynaptic elements including lamina neurons L1 and L2. L1 and L2 express distinct isoforms of the homophilic repulsive protein Dscam2, and since these isoforms cannot bind to each other, cell-specific expression has been proposed to be necessary for preventing repulsive interactions that could disrupt the synapse. Here, we show that the number of synapses are reduced in flies that express only one isoform, and L1 and L2 dendritic morphology is perturbed. We propose that these defects result from inappropriate interactions between L1 and L2 dendrites. We conclude that regulated Dscam2 alternative splicing is necessary for the proper assembly of photoreceptor synapses.
