Expression of 18-wheeler in the follicle cell epithelium affects cell migration and egg morphology in Drosophila

The Drosophila ovary is a model system for examining the genetic control of epithelial morphogenesis. The somatic follicle cells form a polarized epithelium surrounding the 16-cell germ line cyst. The integrity of this epithelium is essential for the successful completion of oogenesis. Reciprocal signaling between germ line and somatic cells establishes embryonic and eggshell polarity. The follicle cells are responsible for shaping the egg and secreting the eggshell. Follicle cells at the boundary between the nurse cells and the oocyte migrate centripetally to cover the anterior end of the oocyte and secrete the operculum. Dorsal anterior main body follicle cells undergo elaborate patterning to produce the dorsal appendages. We have examined the expression of the Toll-like receptor, 18-wheeler (18w), in the ovary and find it to be restricted to subpopulations of follicle cells. Females carrying loss-of-function 18w mutant clones in their ovaries show delayed follicle cell migrations. The eggs laid by such females also show morphological defects in egg shape and dorsal appendage morphology. We propose that the 18W protein plays an adhesive or signaling role in regions of the epithelium engaged in cell migration.