Positional Cues in the Drosophila Nerve Cord: Semaphorins Pattern the Dorso-Ventral Axis |
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Authors: | Marta Zlatic Feng Li Maura Strigini Wesley Grueber Michael Bate |
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Affiliation: | 1.Department of Zoology, University of Cambridge, Cambridge, United Kingdom;2.Department of Physiology and Cellular Biophysics, Columbia University, New York, New York, Unites States of America;3.Howard Hughes Medical Institute (HHMI) Janelia Farm Research Campus, Ashburn, Virginia, United States of America;4.Institute of Molecular Biology and Biotechnology (IMBB)-FORTH, Iraklio, Crete, Greece;Stanford University, United States of America |
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Abstract: | During the development of neural circuitry, neurons of different kinds establish specific synaptic connections by selecting appropriate targets from large numbers of alternatives. The range of alternative targets is reduced by well organised patterns of growth, termination, and branching that deliver the terminals of appropriate pre- and postsynaptic partners to restricted volumes of the developing nervous system. We use the axons of embryonic Drosophila sensory neurons as a model system in which to study the way in which growing neurons are guided to terminate in specific volumes of the developing nervous system. The mediolateral positions of sensory arbors are controlled by the response of Robo receptors to a Slit gradient. Here we make a genetic analysis of factors regulating position in the dorso-ventral axis. We find that dorso-ventral layers of neuropile contain different levels and combinations of Semaphorins. We demonstrate the existence of a central to dorsal and central to ventral gradient of Sema 2a, perpendicular to the Slit gradient. We show that a combination of Plexin A (Plex A) and Plexin B (Plex B) receptors specifies the ventral projection of sensory neurons by responding to high concentrations of Semaphorin 1a (Sema 1a) and Semaphorin 2a (Sema 2a). Together our findings support the idea that axons are delivered to particular regions of the neuropile by their responses to systems of positional cues in each dimension. |
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