Genetic, Genomic, and Biophysical Investigations on the Robust Nature of Morphogenesis: A Study of Drosophila Dorsal Closure

Abstract

Cell sheet morphogenesis is essential for metazoan development and homeostasis, contributing to key developmental stages such as neural tube closure as well as tissue maintenance through wound healing. Dorsal closure, a well-characterized stage in Drosophila embryogenesis, has emerged as a model for cell sheet morphogenesis. Closure is a remarkably robust process where coordination of conserved gene expression and signaling cascades regulate cellular movements that drive closure. While well-characterized, new ‘dorsal closure genes’ continue to be discovered due to advances in microscopy and genetics. Here, we use live imaging and a set of large deletions, deficiencies (Dfs), that together remove 98.9% of the genes on 2L in order to identify regions of the genome required for normal closure. We successfully screened 96.1% of the genes on 2L and identified diverse dorsal closure defects in embryos homozygous for 47 Dfs, 26 of which have no known dorsal closure gene located within the Df region. We have already identified pimples, odd-skipped, paired, and sloppy-paired 1 as dorsal closure genes on the 2L affecting lateral epidermal cell shapes, and anticipate we will continue to identify novel ‘dorsal closure genes’ with further analysis. We also investigate the changes in dorsal closure dynamics and forces in the even-skipped (eve) mutant, which has aberrant cell shapes and behaviors as well as reduced actin and myosin at the purse string, but completes closure. We find that loss of wg/wnt-1 signaling in eve causes the observed defects in closure and that crumbs, a regulator of actin and myosin, is mis-expressed. Additionally, laser microsurgery demonstrates that the eve or wg mutant embryos are under a global tension in the anterior-posterior direction. Lastly, we identify a lesion in echinoid that is responsible for the jagged purse string and ectopic zipping dorsal closure phenotype previously thought to be due to a lesion in Zasp52.