CELLULAR PATHWAYS ACTING ALONG THE GERMBAND AND IN THE AMNIOSEROSA MAY PARTICIPATE IN GERMBAND RETRACTION OF THE DROSOPHILA-MELANOGASTER EMBRYO

Germband retraction in Drosophila melanogaster, like most embryonic mo rphogenetic events in this organism and in higher eukaryotes, is not w ell understood. We have taken several approaches to study the relation ships between previously identified mutations (u-shaped, serpent, hind sight and tailup) that selectively cause germband retraction defects i n homozygous embryos, and a more pleiotropically acting locus, DER/fai nt little ball. Our observations from genetic, immunohistochemical, an d embryo culture experiments suggest that the former four loci are ele ments of at least two parallel and partially redundant cellular pathwa ys that affect germband retraction by acting in amnioserosal developme nt or maintenance. An additional discrete and unique pathway. represen ted by DER/faint little ball, is likely to function in the germband it self. While the role of the amnioserosa during germband retraction app ears to be permissive, the action of DER in the germband may be mediat ed by the cytoskeleton.