Neuron
Volume 70, Issue 2, 28 April 2011, Pages 281-298
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Article
A Combinatorial Semaphorin Code Instructs the Initial Steps of Sensory Circuit Assembly in the Drosophila CNS

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Summary

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.

Highlights

► PlexB establishes chordotonal sensory afferent connectivity within the CNS ► PlexB is a functional receptor for the secreted ligands Sema-2a and Sema-2b ► Sema-2b attraction and Sema-2a repulsion cooperatively direct CNS connectivity ► Sema-2b-PlexB signaling is critical for larval vibration responses

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Present address: Department of Computational and Systems Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15207, USA