In vivo analysis of a Hox gene enhancer required for segment-specific sense organ patterning
Authors: Xinyuan Liu; Teresa Orenic
Affiliation: University of Illinois at Chicago, UIC, Chicago, IL
Keywords: c. homeotics; e. enhancers
Hox genes encode conserved transcription factors (TFs) that specify segmental or regional identity along the anterior-posterior (A/P) axis of developing animal embryos and also function during later developmental stages in patterning of limbs and other organs. During embryonic development, the Hox TFs function at the top of the hierarchy that controls intra-segmental patterning to generate differences in segmental/regional patterning. On the other hand, recent studies in Drosophila and other insects suggest that the Hox genes are targets of intra-segmental patterning genes and function downstream of these genes to generate morphological differences among limbs. We are investigating the regulation of the Hox gene Sex combs reduced (Scr) in response to the intra-segmental patterning networks that control development of the Drosophila adult legs. Scr is expressed throughout T1 legs, but its expression is elevated in defined domains of developing legs within the primordia of a group sense organs, the transverse bristle rows (TBRs). We have identified an Scr enhancer (ScrE) that drives expression in the TBR primordia and is required for TBR development in T1 legs. Furthermore, the proximal/distal (P/D) patterning genes Distalless (Dll) and bric-a-brac1/2 (bab1/2) regulate Scr expression through the enhancer. Dll, a homeodomain (HD) TF, activates Screxpression through multiple sites dispersed throughout the ScrE enhancer. In addition, ScrE is responsive to repression by Bab1/2 TFs and potential Bab-response sequences have been mapped to a 78bp conserved block within ScrE. An in vivo functional analysis of these sequences is in progress to determine the necessity of these sites for Scr expression and patterning of T1 leg sensory organs. This investigation will provide insight into how Hox gene integration of intra-segmental patterning information leads to the development of segment-specific limb morphologies.