Fig. 7.

A model for formation of the FSC niche and derivation of Pak mutant phenotypes. Anterior is to the left in all panels. (A) Development of wild-type ovariole. Mature germline cyst at tip of the basal stalk in the pupal ovary guides establishment of two FSC niches containing FSCs (magenta). Cysts are encapsulated one at a time in the resulting germarium. (B) Development of Pak mutant ovariole. Due to a failure in cell intercalation, Pak mutants form abnormally wide basal stalks, enabling side-by-side cysts and the anchoring of four FSCs in at least three niches (the two internal FSCs might share a niche). The resulting germarium is capable of encapsulating two cysts at a time. (C) As the Pak mutant germarium ages, the side-by-side cysts become unsynchronized and are packaged individually, resulting in the phenotype of unpaired cysts on either side of an aberrant stalk.