Dual role of extramacrochaetae in cell proliferation and cell differentiation during wing morphogenesis in Drosophila.

The Extramacrochaetae (emc) gene encodes a transcription factor with an HLH domain without the basic region involved in interaction with DNA present in other proteins that have this domain. EMC forms heterodimers with bHLH proteins preventing their binding to DNA, acting as a negative regulator. The function of emc is required in many developmental processes during the development of Drosophila, including wing morphogenesis. Mitotic recombination clones of both null and gain-of-function alleles of emc, indicate that during wing morphogenesis, emc participates in cell proliferation within the intervein regions (vein patterning), as well as in vein differentiation. The study of relationships between emc and different genes involved in wing development reveal strong genetic interactions with genes of the Ras signalling pathway (torpedo, vein, veinlet and Gap), blistered, plexus and net, in both adult wing phenotypes and cell behaviour in genetic mosaics. These interactions are also analyzed as variations of emc expression patterns in mutant backgrounds for these genes. In addition, cell proliferation behaviour of emc mutant cells varies depending on the mutant background. The results show that genes of the Ras signalling pathway are co-operatively involved in the activity of emc during cell proliferation, and later antagonistically during cell differentiation, repressing EMC expression.