Genes required for cell rearrangements in Drosophila. J. Zallen 1, E. Schejter 2, E. Wieschaus 1. 1) Dept Molecular Biology, Princeton Univ, Princeton, NJ; 2) Dept Molecular Genetics, Weizmann Institute, Rehovot, Israel.
An organized body structure arises from the morphogenesis of cell populations through changes in cell number, shape and arrangement. Several key processes of development are driven by active cell rearrangements. During convergent extension in vertebrates and germband extension in Drosophila, directed cell intercalation causes a tissue to elongate along one axis and simultaneously shorten along the perpendicular axis. This change in tissue morphology may reflect dynamic regulation of cell adhesion and motility.
Changes in cell motility often involve polarized mobilization of the actin cytoskeleton to generate directed cell movement. In particular, members of the WASP/SCAR protein family function together with the actin-associated Arp2/3 complex to stimulate actin filament formation. We found that Drosophila Scar mutants exhibit germband extension defects, possibly due to a reduction in cell intercalation. In contrast, Wasp mutants extend their germbands normally. These results suggest that the regulation of cell motility may underlie cell movements during germband extension.
To identify zygotic genes that direct germband extension together with Scar, we screened the deficiency kits from the Bloomington Drosophila Stock Center, which remove ~70% of the euchromatic genome. By examining living embryos for mutants which fail to complete germband extension, we identified regions of the genome that are required for this process. Many of these regions uncover known genes involved in embryonic patterning and cell division; however, several regions may uncover loci specifically required for germband extension. Further phenotypic and molecular analysis of these regions is in progress.