In Vivo Analysis of the coracle Dorsal Closure Defect in Drosophila

Yelena Burtseva
Duke University

Coracle is a member of the Protein 4.1 superfamily of proteins, which consists of Protein 4.1, the Neurofibromotosis 2 tumor suppressor merlin, Expanded, the ERM proteins, protein tyrosine phosphatases, and unconventional myosins. Members of this family have a variety of functions ranging from structural linkage between transmembrane proteins and the actin cytoskeleton to regulation of cell signaling events such as cell proliferation and cytoskeleton rearrangement. Coracle has been shown to be localized to the septate junction in epithelial cells and is required for the maintenance of the transepithelial barrier. Null coracle mutations result in embryonic lethality and failure in dorsal closure. To further examine this phenotype, we took time series images of living mutant embryos starting at the beginning of the dorsal closure process and continuing for the next 16 hours. Remarkably, even though we see a dorsal hole phenotype in cuticle preparations, we find that most of the mutant embryos complete dorsal closure and subsequently re-open dorsally. Also, although coracle is not expressed at the leading edge of the lateral epithelium or in the amnioserosa, we find tearing of the amnioserosa cell sheet from the leading edge epithelial cells. Currently, we are working on two possibilities that might explain these results. The first is apoptosis of amnioserosa occurring due to developmental delay of coracle mutants. The second is an adhesion defect between the amnioserosa and epithelial cells at the leading edge.

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