Genetic and expression analysis of enabled in Drosophila leg segmentation

Abstract

Drosophila leg segmentation is a process which is beginning to be understood. The Notch (N) signaling pathway has been identified as a key regulator of joint formation and segmental growth in Drosophila legs. In this context, four-jointed (fj) is thought to be an effector of N signaling based on the partial similarity of its phenotype, its regulation by N activity and its action upon the transcription of N ligands. enabled (ena) has been identified as a dominant enhancer of the fj phenotype and is also a member of the abelson-disabled-ena pathway, which has been studied for its role in embryonic axonogenesis. In addition, ena has been shown to play a role in F-actin polymerization. In this study, we show that ena also acts as a dominant enhancer of dachs (d) mutants, whose mutation is similar to fj⁻ in the leg. Study of Ena expression in the leg disc during early pupation shows that it is expressed ubiquitously but up-regulated in the middle of the future segments where Delta is expressed and it is excluded from cells where N signaling is active. Ena is also shown to be enriched at the adherens junctions, suggesting a role in adherens junctions formation/maintenance or signaling at these junctions. Phenotypic analysis suggests that ena⁻ is cell lethal in loss-of-function clones and that it is not dosage-sensitive when over-expressed in the leg. In addition, the inter-dependency of the fj and abl pathways is supported by the demonstration that an abl interacting locus also interacts with fj. Therefore, ena may participate in leg segmentation by signaling at the adherens junctions and this response may depend on N, fj and abl signaling pathways, which all participate in the leg segmentation process. Therefore, Ena probably acts as a linking molecule between signaling and the actin cytoskeleton to perform the morphogenetic work necessary for leg segmentation.