Misshapen orders an egg roll

A protein kinase shapes Drosophila egg chambers by promoting cell migration, Lewellyn et al. reveal.

Fly egg chambers contain an inner core of germ cells surrounded by a layer of epithelial follicle cells and an overlying basement membrane. During development, the follicular epithelium polarizes and migrates perpendicular to the anterior–posterior axis of the egg chamber so that the entire chamber rotates within the basement membrane. This movement appears to organize the basement membrane into fibrils that encircle the egg chamber, forming a corset that may help the spherical egg chamber elongate.

The follicular epithelium fails to polarize in the absence of a protein kinase called Misshapen (Msn), resulting in abnormally rounded eggs. Lewellyn et al. found that individual follicle cells lacking Msn were immotile. Neighboring wild-type cells continued to migrate, and, if enough cells maintained Msn expression, the epithelium as a whole could move and rotate the egg chamber.

Depleting Msn increased the amount of integrin adhesion receptors at the basal surface of follicle cells, keeping them stuck to the basement membrane and unable to organize it into fibrils. Partially reducing integrin levels rescued follicle cell motility and basement membrane organization. Lowering integrin levels also restored the overall planar polarity of the follicular epithelium, suggesting that the tissue’s polarization arises from the motility of the individual follicle cells. Senior author Sally Horne-Badovinac now wants to investigate how the follicle cells collectively choose their migration direction and to determine how Msn regulates integrin levels.