A genetic screen for novel genes involved in tracheal development in Drosophila melanogaster

Many animal organs are built of ramified tubular epithelial structures. How they form and what controls branching events, direction of growth and tube size are important questions for understanding branch morphogenesis. The Drosophila tracheal (respiratory) system is an excellent model to investigate this process. Extensive studies on tracheal development in the last years resulted in revealing mechanisms involved in tube formation. However there are still many open questions, especially concerning late events of tracheal morphogenesis, such as branching of terminal cells during the larval life. Thus we performed a genetic mosaic screen to identified new genes involved in tracheal development. As a screening tool the MARCM system was applied and mutant lines were examined in third instar larvae. Out of 4779 analysed lines 344 showed phenotypes different from the wild type. These lines were classified into five general phenotypic classes: A - no mutant clones, B - low number of mutant clonal cells, C - small mutant clonal cells, D - dorsal trunk defects, E - terminal branching defects. Three phenotypic groups were characterised in more detail - one from class D, showing dorsal trunk bendings and consisting of eight alleles (D1), and two from class E, showing defects in formation of lumen in terminal cells (E2 and E3), both consist of two alleles. The phenotypes in groups D1 and E3 were mapped to the genomic region of ~190kb and ~160kb respectively. Although none of the mutations have been mapped to individual genes and no mechanisms explaining different phenotypes could be proposed, the screen provided collection of mutants, whose analysis will help in better understanding of cellular processes of tracheal development