GENES REQUIRED FOR EMBRYONIC MUSCLE DEVELOPMENT IN DROSOPHILA-MELANOGASTER - A SURVEY OF THE X-CHROMOSOME

We have begun a genetic analysis to dissect the process of myogenesis by surveying the X chromosome of Drosophila melanogaster for mutations that affect embryonic muscle development. Using polarised light micro scopy and antibody staining techniques we analysed embryos hemizygous for a series of 67 deletion mutations that together cover an estimated 85% of the X chromosome, or 16.5% of the genome. Whereas the mature w ild type embryo has a regular array of contractile muscles that insert into the epidermis, 31 of the deletion mutants have defects in muscle pattern, contractility or both, that cannot be attributed simply to e pidermal defects and identify functions required for wild type muscle development. We have defined mutant pattern phenotypes that can be des cribed in terms of muscle absences, incomplete myoblast fusion, failur e of attachment of the muscle to the epidermis or mispositioning of at tachment sites. Thus muscle development can be mutationally disrupted in characteristic and interpretable ways. The areas of overlap of the 31 deletions define 19 regions of the X chromosome that include genes whose products are essential for various aspects of myogenesis. We con clude that our screen can usefully identify loci coding for gene produ cts essential in muscle development.