How Drosophila (Diptera : Drosophilidae) follicles become spatially organized and obtain their ovoid shape

The formation of a Drosophila (Diptera : Drosophilidae) follicle in the germarium requires complex cellular interactions between the germ-line cells and the somatic follicle cells. We have disturbed these morphogenetic processes by incubating germaria with the tripeptide arginine-glycine-aspartic acid (RGD) and culturing them in ovo^D1 host flies. This treatment often resulted in fused follicles (absence of stalk cells) or abnormal follicles with respect to the position and/or number of the oocytes. The follicular phenotypes of the mutants dicephalic (dic) and egalitarian (egl^RC12) suggest that the polarity of the follicular epithelium depends on the position of the oocyte (dic) or of the potential oocyte (egl^RC12) in the follicle. However, in the mutant benign gonial cell neoplasm (bgcn), in which the germ-line cells do not differentiate cytologically, the differentiation of the follicle cells can proceed normally for some time, albeit usually not with the correct axial polarity. Surprisingly, groups of tumour cells differ with respect to the concentration of the vasa protein in the cytoplasm and hence may possess different developmental properties. The ovoid shape of the follicle might result from mechanical constraints exerted by structural elements in circular orientation, i.e. perpendicular to the long axis of the ovariole; microfilament bundles in the follicular epithelium and laminin in the basement membrane are organized in this way. The microfilament bundles may be tethered to the membranes of adjacent cells via PSß integrins.