The receptor tyrosine phosphatase Dlar and integrins organize actin filaments in the Drosophila follicular epithelium.

BACKGROUND: Regulation of actin structures is instrumental in maintaining proper cytoarchitecture in many tissues. In the follicular epithelium of Drosophila ovaries, a system of actin filaments is coordinated across the basal surface of cells encircling the oocyte. These filaments have been postulated to regulate oocyte elongation; however, the molecular components that control this cytoskeletal array are not yet understood.
RESULTS: We find that the receptor tyrosine phosphatase (RPTP) Dlar and integrins are involved in organizing basal actin filaments in follicle cells. Mutations in Dlar and the common beta-integrin subunit mys cause a failure in oocyte elongation, which is correlated with a loss of proper actin filament organization. Immunolocalization shows that early in oogenesis Dlar is polarized to membranes where filaments terminate but becomes generally distributed late in development, at which time beta-integrin and Enabled specifically associate with actin filament terminals. Rescue experiments point to the early period of polar Dlar localization as critical for its function. Furthermore, clonal analysis shows that loss of Dlar or mys influences actin filament polarity in wild-type cells that surround mutant tissues, suggesting that communication between neighboring cells regulates cytoskeletal organization. Finally, we find that two integrin alpha subunits encoded by mew and if are required for proper oocyte elongation, implying that multiple components of the ECM are instructive in coordinating actin fiber polarity.
CONCLUSIONS: Dlar cooperates with integrins to coordinate actin filaments at the basal surface of the follicular epithelium. To our knowledge, this is the first direct demonstration of an RPTP's influence on the actin cytoskeleton.