SOMATIC MESODERM DIFFERENTIATION AND THE DEVELOPMENT OF A SUBSET OF PERICARDIAL CELLS DEPEND ON THE NOT ENOUGH MUSCLES (NEM) LOCUS, WHICH CONTAINS THE INSCUTEABLE GENE AND THE INTRON LOCATED GENE, SKITTLES

Not enough muscles (nem) mutants of Drosophila reveal defects in the d evelopment of embryonic muscles, a subset of pericardial cells, the CN S and derivatives of the PNS (Burchard, S., Paululat, A., Hint, U. and Renkawitz-Pohl, R. (1995) The mutant not enough muscles (nem) reveals reduction of the Drosophila embryonic muscle pattern. J. Cell. Sci. 1 08, 1443-1454). The molecular analysis of the nem locus shows a comple x genomic structure. One transcription unit was identified as inscutea ble (insc). Within the first intron of inse we find another independen t gene, skittles (sktl), which is not affected in nem mutants. inse tr anscripts are localised apically in neuroblasts and may prefigure the localisation of the protein. The skittles mRNA is ubiquitously distrib uted during early embryogenesis due to maternal contribution. Later, s ome enrichment of sktl is observed in the nervous system and the mesod erm. The muscle phenotype shows deletions as well as duplication of sp ecific muscles which is reflected in a change of even-skipped (eve) an d Kruppel (Kr) expressing cells. Our data suggest a role for inse in t he specification process of a subset of muscle progenitors/founders. F urthermore, in inse mutants the eve expressing pericardial cells of th e developing heart are significantly reduced in numbers. (C) 1997 Else vier Science Ireland Ltd.