Nuclear Paxillin Modulates Alternative Splicing Programs in Neurons during Sensitive Periods of Brain Development

During sensitive postnatal periods, brain neural circuits undergo significant refinement coincident with widespread neuronal alternative splicing events in which h undreds of genes alter their splice site selection to generate isoforms essential for synaptic plasticity. Here, we reveal that neuronal activity-dependent serine119 phosphorylation of paxillin (p-paxillin S119) acts as a molecular switch in the nucleus to modulate alternative splicing during this period. We report that following NMDA receptor activation, nuclear p-paxillin S119 is recruited to nuclear speckles, where it interacts with U2AFs and splicing factors. Neuronal paxillin expression is required for timely alternative splicing of synaptic factors, including Snap25. Consequently, young mice lacking paxillin S119 phosphorylation exhibit significantly reduced levels of Snap25-5b isoforms, impaired presynaptic function at hippocampal Schaffer collateral-CA1 synapses, and deficits in short-term learning and memory. These findings support the idea that nuclear p-paxillin S119 is a critical mediator of alternative splicing programs in postnatal neurons during a sensitive period essential for neural plasticity.在出生后敏感发育期，大脑神经环路会发生显著重塑，同时伴随广泛的神经元可变剪接事件：数百个基因会改变其剪接位点选择，以生成对突触可塑性至关重要的剪接异构体。本研究揭示，神经元活动依赖的桩蛋白（paxillin）丝氨酸119位点磷酸化（p-paxillin S119）可作为细胞核内的分子开关，在该时期调控可变剪接。我们发现，在N-甲基-D-天冬氨酸受体（NMDA受体）激活后，细胞核内的p-paxillin S119会被招募至核斑，并与U2小核核糖核蛋白辅助因子（U2AFs）及剪接因子相互作用。神经元桩蛋白的表达对于突触相关因子（包括突触体相关蛋白25（Snap25））的按时可变剪接是必需的。因此，缺失paxillin S119磷酸化位点的幼年小鼠，其Snap25-5b剪接异构体的水平会显著降低，海马Schaffer侧支-CA1突触的突触前功能受损，且短期学习与记忆存在缺陷。上述研究结果支持以下观点：细胞核内的p-paxillin S119是出生后敏感发育期神经元可变剪接程序的关键调控介质，而该发育期对神经可塑性至关重要。