Caracterización de elementos reguladores en "cis" del Complejo "Iroquois" de "Drosophila melanogaster": control transcripcional por las vías de comunicación intercelular Dpp y EGFR

Abstract

The Iroquois Complex (Iro-C) genes of D. melanogaster encode homeodomain-containing regulatory proteins. These genes are expressed at different domains in the imaginal discs, where they contribute to regional specification and pattern formation. lt has been suggested their expression to be controlled by multiple and shared position-specific cis-regulatory elements (Gómez-Skarmeta y cols., Cell 85, 95-105, 1996). In this project first, we have identified several cis-control I ing elements of the !ro-C that drive expression of the reporter gene LacZ at specific domains of the wing imagina] disc. None of the identified elements on its own mediates the complete !ro-C pattern of expression in the wing disc, thus reinforcing the hypothesis of the existence of rnultiple cis-controlling elements in the Iro-C. One of the regulatory elements (named elro') mediates LacZ expression in the presumptive notum region of the wing disc in a pattern very similar to that of the Iro-C genes. Gain-of-function and loss-of-function conditions of the Dpp and EGFR signalling pathways, which regulate the expression of the Iro-C genes, similarly affect expression of the elro`-LacZ transgene. This enhancer contains several putative binding sites for transcription factors effectors of the Dpp and EGFR signalling pathways, namely, the ETS transcription factor Pointed (Pnt) and the GATA factor Pannier (Pnr). Some of them are evolutionarily conserved. Their functionality in vivo has been assayed by the generation of transgenic fijes carrying truncated or niutated versions of the original elro' element. Our results indicate that Pnt carries out the EGFR-dependent activation of the lro-C genes, at least in part, through the elro' element. Dpp-dependent repression of the /ro-C genes in the prospective medial notum appears to be effected by a Pnr/Ush heterodimer, also through this regulatory element. In addition, we have identified putative repressor elements that should mediate Dpp-dependent repression of !ro-C genes at the prospective hinge reglan of the irnaginal wing disc. Thus, our results suggest that the restricted expression of the !ro-C genes in the prospective notum of the wing disc and, accordingly the especification of this territory and the formation of the 'ganen' of the sensory organs, results at least in part from the convergence of opposing signals from the EGFR and Dpp pathways on the elro' enhancer.