Analysis of follicle-cell functions in Drosophila: the Fs(3)Apc mutation and the development of chorionic appendages.

Fs(3)Apc is a dominant female-sterile mutation of Drosophila melanogaster which causes an incomplete migration of follicle cells between the oocyte and the nurse cells. This leads to leakage of anterior egg cytoplasm followed by degeneration of the egg primordium or deposition of flaccid eggs with reduced anterior egg coverings including the dorsal appendages. Analysis of ovarian and germ-line chimeras revealed that the focus of the Apc phenotype is located in the ovarian soma. Apc+ clones, induced by mitotic recombination, lead to the formation of "exceptional" eggs with (often partial) rescue of the mutant phenotype. Analysis of Apc+ mosaics shows that the Apc mutant phenotype depends on the genotype of the anterior follicle cells. The patterns of apparent Apc+ clones suggest that there is no lineage restriction between the follicle cells that form the anterior egg coverings and those that form the dorsal appendages at the follicle envelope stage.