Drosophila semaphorin2b is required for the axon guidance of a subset of embryonic neurons

Mark M Emerson,Jennifer B Long,David Van Vactor

doi:10.1002/dvdy.23979

Abstract

Background: The process of axon guidance is important in establishing functional neural circuits. The differential expression of cell-autonomous axon guidance factors is crucial for allowing axons of different neurons to take unique trajectories in response to spatially and temporally restricted cell non-autonomous axon guidance factors. A key motivation in the field is to provide adequate explanations for axon behavior with respect to the differential expression of these factors. Results: We report the characterization of a predicted secreted semaphorin family member, semaphorin2b (Sema-2b) in Drosophila embryonic axon guidance. Misexpression of Sema-2b in neurons causes highly penetrant axon guidance phenotypes in specific longitudinal and motoneuron pathways; however, expression of Sema-2b in muscles traversed by these motoneurons has no effect on axon guidance. In Sema-2b loss-of-function embryos, specific motoneuron and interneuron axon pathways display guidance defects. Specific visualization of the neurons that normally express Sema-2b reveals that this neuronal cohort is strongly affected by Sema-2b loss-of-function alleles. Conclusions: While secreted semaphorins have been implicated as cell non-autonomous chemorepellants in a variety of contexts, here we report previously undescribed Sema-2b loss-of-function and misexpression phenotypes that are consistent with a cell-autonomous role for Sema-2b. Developmental Dynamics 242:861–873, 2013. © 2013 Wiley Periodicals, Inc.Key FindingsMisexpression of the secreted semaphorin Sema-2b in neurons results in specific axon guidance phenotypes.Both Sema-2b loss-of-function and misexpression phenotypes are congruent with a cell-autonomous role for Sema-2b.Novel axon guidance phenotypes caused by Sema-2b loss-of-function mutations are characterized.

Highlights

A key component in the development of the nervous system is the process of axon guidance in which a neuron extends a process to its post-synaptic target
While the immense complexity of some nervous systems suggested that many signaling pathways are employed during development, it has become increasingly clear that several conserved pathways are used repeatedly to shape the development of different neural circuits throughout the embryo
We adopted a misexpression approach in the Drosophila embryo to aid in the recovery of differentially expressed factors that contribute to the specificity of individual axon guidance decisions

Summary

Background

The process of axon guidance is important in establishing functional neural circuits. Results: We report the characterization of a predicted secreted semaphorin family member, semaphorin2b (Sema-2b) in Drosophila embryonic axon guidance. Misexpression of Sema-2b in neurons causes highly penetrant axon guidance phenotypes in specific longitudinal and motoneuron pathways; expression of Sema-2b in muscles traversed by these motoneurons has no effect on axon guidance. Conclusions: While secreted semaphorins have been implicated as cell non-autonomous chemorepellants in a variety of contexts, here we report previously undescribed Sema-2b loss-of-function and misexpression phenotypes that are consistent with a cell-autonomous role for Sema-2b. VC 2013 Wiley Periodicals, Inc. Key Findings: Misexpression of the secreted semaphorin Sema-2b in neurons results in specific axon guidance phenotypes. Key Findings: Misexpression of the secreted semaphorin Sema-2b in neurons results in specific axon guidance phenotypes Both Sema-2b loss-of-function and misexpression phenotypes are congruent with a cell-autonomous role for Sema-2b. Novel axon guidance phenotypes caused by Sema-2b loss-of-function mutations are characterized

INTRODUCTION

RESULTS

DISCUSSION

EXPERIMENTAL PROCEDURES