Cell Sheet and Actin Appendage Morphogenesis
We utilize novel biophysical strategies in concert with modern molecular genetic and reverse genetic approaches in Drosophila to explore the forces that are responsible for cell shape change and movements during morphogenesis. This work is a collaboration with Glenn Edwards’ group in Physics and with Stephanos Venakides group in Mathematics.
Dorsal closure is a key step in Drosophila morphogenesis in which two embryonic tissues, the amnioserosa and lateral epidermis, undergo cell shape changes and movements to enclose the amnioserosa and form a seamless dorsal epithelium. A canthus forms where two opposing sheets of lateral epidermis first meet and begin to produce a seam. Through studies of the three-dimensional aspect of each canthus and studies of closure when both canthi have been removed, we discover the importance of this structure for native closure behavior.
Both the amnioserosa and a supracellular purse string in the leading edge of the lateral epidermis contribute to the movements of dorsal closure. We have developed techniques to extract data from confocal fluorescent 4D data sets of dorsal closure in order to analyze the cell shape changes and movements associated with wild type and genetically or biophysically disrupted closure.
Dorsal closure proceeds even if we laser ablate one (but NOT both!) of the tissues responsible for closure. This indicates that this model epithelial cell sheet movement depends on redundant forces that, in concert, drive morphogenesis. We show that the magnitude of each force is significantly larger than their vector sum, indicating that there is both potential for generating larger forces and the successful morphogenesis requires that the forces applied be precisely balanced.
How molecular events are regulated such that large, opposing forces efficiently drive morphogenesis remains a mystery, but we are currently pursuing leads that point to two distinct pathways: the bidirectionally signaling integrin cell surface receptors and mechanically gated ion channels.
We are also interested in the morphogenesis of actin based appendages in Drosophila hairs and bristles). Severe mutations in crinkled (ck), the gene that encodes MyoVIIa, display defects in hair and bristle morphology, suggesting ck/MyoVIIa is involved in the formation of actin-based structures. We are working to identify proteins and/or cargo that interact with ck/MyoVIIa and further examine the molecular mechanism behind ck/MyoVIIa’s role in the formation and maintenance of actin-based structures. In addition to hair and bristle formation, we are examining the morphology of actin-rich structures in early Drosophila development.