BEHAVIOR OF EXTRAMACROCHAETAE MUTANT-CELLS IN THE MORPHOGENESIS OF THE DROSOPHILA WING

The gene extramacrochaetae (emc) encodes a non-basic Helix-loop-helix (HLH) protein that interacts and antagonises other basic-HLH proteins. The expression pattern of emc, and the phenotype of lethal emc allele s indicate that this gene is operative in several developmental proces ses. Here we study the requirements for emc during cell proliferation and vein differentiation in the wing. Mosaic analysis of hypomorphic c onditions of emc reveals the tendency of mutant cells to proliferate a long the veins as long stripes. Large clones abuting two adjacent vein s obliterate the corresponding inter-vein, affecting the size and shap e of the whole wing. Thus, the emc gene participates in the control of cell proliferation within inter-vein regions in the wing. Similar eff ects were found in the haltere and in the leg, The behavior of emc cel ls in genetic mosaics indicate that (1) proliferation is locally contr olled within inter-vein sectors, (2) cells proliferate according to th eir genetic activity along preferential positions in the wing morphoge netic landscape and (3) cell proliferation in the wing is integrated b y 'accommodation' between mutant and wild type cells.