Fig. 3. hop mutants produce polar cells at the expense of stalk cells. The identity of polar cell fates was assayed using the molecular markers Fas III (in red) and PZ80 (in green) with nuclear staining by DAPI (in blue). In wild-type ovaries (A), Fas III protein is found at high levels in the membranes of all follicle cells of the germarium, but is markedly reduced in all but the polar cells of egg chambers of the vitellarium. ß-galactosidase produced in the PZ80 enhancer trap is not detectable until approximately stage 4, after the egg chamber has exited the germarium. At that time, ß-galactosidase is visible specifically in the two polar cells at each end of the egg chamber. (B) In the intermediate mutant combination hopmsv/hopM75, there are extra polar cells, as indicated by the appearance of both Fas III and PZ80 (arrowheads). The number of polar cells is even greater in more severe mutant combinations, such as hopmsv/hopGA32 (C). The expression of the lacZ enhancer trap line, 93F, was used to mark the stalk cells in wild-type (D), and hop mutant (E and F) ovarioles. In wild type (D) 93F strongly marks the terminal filament (arrow) and the interfollicular stalk cells (arrowheads). In hopmsv/hopM75 (E), there are consistently fewer ß-galactosidase positive interfollicular cells (arrows). In strong mutant combinations, such as hopmsv/hopM38 (F), stalk cells are rare or absent in extensively fused ovarioles. Additional loss of one copy of the upd gene enhances the phenotype of hop mutants. The hopmsv/hopM4 heteroallelic combination shows nearly normal ovarioles (G), with only occasional extra polar cells, as indicated by Fas III (red) and PZ80 (green) and marked by arrows (see Table 1) and rare chamber fusions. However, these phenotypes are dramatically enhanced in hopmsv updYM55/hopM4 females (H).
