The Solomon H. Snyder Department of Neuroscience, The Johns Hopkins University School of Medicine, Howard Hughes Medical Institute, Baltimore, MD 21205, USA.
Neuron. 2011 Apr 28;70(2):281-98. doi: 10.1016/j.neuron.2011.02.050.
Longitudinal axon fascicles within the Drosophila embryonic CNS provide connections between body segments and are required for coordinated neural signaling along the anterior-posterior axis. We show here that establishment of select CNS longitudinal tracts and formation of precise mechanosensory afferent innervation to the same CNS region are coordinately regulated by the secreted semaphorins Sema-2a and Sema-2b. Both Sema-2a and Sema-2b utilize the same neuronal receptor, plexin B (PlexB), but serve distinct guidance functions. Localized Sema-2b attraction promotes the initial assembly of a subset of CNS longitudinal projections and subsequent targeting of chordotonal sensory afferent axons to these same longitudinal connectives, whereas broader Sema-2a repulsion serves to prevent aberrant innervation. In the absence of Sema-2b or PlexB, chordotonal afferent connectivity within the CNS is severely disrupted, resulting in specific larval behavioral deficits. These results reveal that distinct semaphorin-mediated guidance functions converge at PlexB and are critical for functional neural circuit assembly.
果蝇胚胎中枢神经系统中的纵向轴突束为身体各节段之间提供了连接，并为沿前后轴的协调神经信号传递提供了必要条件。我们在这里表明，特定中枢神经系统纵向束的建立以及对同一中枢神经系统区域的精确机械感觉传入神经支配的形成是由分泌的 semaphorin Sema-2a 和 Sema-2b 协调调节的。Sema-2a 和 Sema-2b 都利用相同的神经元受体plexin B（PlexB），但具有不同的导向功能。局部的 Sema-2b 吸引促进了一组中枢神经系统纵向投射的初始组装，随后将 chordotonal 感觉传入轴突靶向到这些相同的纵向连接上，而更广泛的 Sema-2a 排斥则有助于防止异常的神经支配。在没有 Sema-2b 或 PlexB 的情况下，中枢神经系统内的 chordotonal 传入连接严重受损，导致特定的幼虫行为缺陷。这些结果表明，不同的 semaphorin 介导的导向功能在 PlexB 处汇聚，并对功能性神经回路组装至关重要。
