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 i n other proteins that have this domain. EMC forms heterodimers with bHLH pr oteins preventing their binding to DNA, acting as a negative regulator. The function of emc is required in many developmental processes during the dev elopment of Drosophila, including wing morphogenesis. Mitotic recombination clones of both null and gain-of-function alleles of emc, indicate that dur ing wing morphogenesis, emc participates in cell proliferation within the i ntervein regions (vein patterning), as well as in vein differentiation. The study of relationships between erne and different genes involved in wing d evelopment reveal strong genetic interactions with genes of, the Ras signal ling pathway (torpedo, vein, veinlet and Gap), blistered, plexus and net, i n both adult wing phenotypes and cell behaviour in genetic mosaics. These i nteractions are also analyzed as variations of emc expression patterns in m utant backgrounds for these genes. In addition, cell proliferation behaviou r of emc mutant cells varies depending on the mutant background. The result s show that genes of the Ras signalling pathway are co-operatively involved in the activity of emc during cell proliferation, and later antagonistical ly during cell differentiation, repressing EMC expression. (C) 1999 Elsevie r Science Ireland Ltd. All rights reserved.