Abstract
Abl tyrosine kinase and its effectors among the Rho family of GTPases each act to control dendritic morphogenesis in Drosophila. It has not been established, however, which of the many GTPase regulators in the cell link these signaling molecules in the dendrite. In axons, the bifunctional guanine exchange factor, Trio, is an essential link between the Abl tyrosine kinase signaling pathway and Rho GTPases, particularly Rac, allowing these systems to act coordinately to control actin organization. In dendritic morphogenesis, however, Abl and Rac have contrary rather than reinforcing effects, raising the question of whether Trio is involved, and if so, whether it acts through Rac, Rho or both. We now find that Trio is expressed in sensory neurons of the Drosophila embryo and regulates their dendritic arborization. trio mutants display a reduction in dendritic branching and increase in average branch length, whereas over-expression of trio has the opposite effect. We further show that it is the Rac GEF domain of Trio, and not its Rho GEF domain that is primarily responsible for the dendritic function of Trio. Thus, Trio shapes the complexity of dendritic arbors and does so in a way that mimics the effects of its target, Rac.
Highlights
Dendrites are the receptive units of neurons, dictating their connectivity and utility by their specialized, often elaborate shapes
The md-da sensory neurons of the peripheral nervous system (PNS) cover the entire body wall of Drosophila larvae and have a stereotypic arrangement in each abdominal segment. These neurons have been grouped in four Classes depending on their dendritic complexity, starting with very simple ‘‘Class I’’ neurons, to very complex ‘‘Class IV’’ neurons [29,30]. We have used this system to investigate the function of Trio in dendritic morphogenesis in the present study
Trio is expressed in the peripheral sensory neurons of Drosophila
Summary
Dendrites are the receptive units of neurons, dictating their connectivity and utility by their specialized, often elaborate shapes. Trio was originally isolated genetically as an enhancer of the Abl mutant phenotype, showing dosage-sensitive genetic interactions with Abl pathway genes in various axon growth and guidance assays and for organismal viability, and this led to its assignment as a core component of the Abl pathway [25] Given that both Rho GTPases and Abl are potent regulators of dendritic morphogenesis, the potential role of Trio as a linker between them in dendrites becomes a critical question. Trio affects higher order branches selectively, suggesting its role is largely focused on regulation of these more dynamic, actin-rich dendritic branches
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