On the Shark quest: Role of Shark tyrosine kinase in tube formation

Many organs develop from flat sheets of cells that reorganize into tubes.  Errors in this process result in common birth defects, such as neural tube defects.  A powerful genetic model system for studying tube development is dorsal appendage (DA) formation in the Drosophila egg chamber.  During egg chamber development, a subset of the somatic follicle cells, which surround the oocyte and its 15 germline nurse cells, rearrange to make long thin tubes.  Previous work has shown that the development of DA tubes requires the bullwinkle-shark pathway.  Bullwinkle (Bwk) is a transcription factor that acts in the germ cells to regulate a signal to the Shark tyrosine kinase, which is required in the follicle cells for proper DA tube formation.  Germline mutations in bwk cause failure of the tube to close and deformation of DA’s.  The role of Shark in this pathway is less clear.  How is Shark functioning in the bullwinkle-shark pathway? Preliminary data suggest that Shark localization might be important.  To test this hypothesis, I am using two approaches.  I am making transgenic flies that will express a fluorescently tagged Shark in order to follow its localization during DA tube formation.  I am also performing in situ hybridization to analyze shark mRNA localization in wild type vs. bwk mutants.  We expect to gain understanding of Shark localization and function.  Since Bwk and Shark are highly conserved, our findings will likely contribute to a general understanding of the causes of birth defects in humans.