ALPHA-SPECTRIN IS REQUIRED FOR OVARIAN FOLLICLE MONOLAYER INTEGRITY IN DROSOPHILA-MELANOGASTER

To understand the role of the spectrin-based membrane skeleton in gene rating epithelial polarity, we characterized the distribution of membr ane skeletal components in Drosophila ovarian follicle cells and in so matic clones of mutant cells that lack alpha-spectrin. Immunolocalizat ion data reveal that wild-type follicle cells contain two populations of spectrin heterodimers: a network of alpha beta heterodimers concent rated on the lateral plasma membrane and an alpha beta(H) population t argeted to the apical surface. Induction of somatic clones lacking alp ha-spectrin leads to follicle cell hyperplasia. Surprisingly, eliminat ion of alpha-spectrin from follicle cells does not appear to prevent t he assembly of conventional beta-spectrin and ankyrin at the lateral d omain of the follicle cell plasma membrane, However, the alpha-subunit is essential for the correct localization of beta(H)-spectrin to the apical surface, As a consequence of disrupting the apical membrane ske leton a distinct sub population of follicle cells undergoes unregulate d proliferation which leads to the loss of monolayer organization and disruption of the anterior-posterior axis of the oocyte. These results suggest that the spectrin-based membrane skeleton is required in a de velopmental pathway that controls follicle cell monolayer integrity an d proliferation.