Fig. 6. PAP has an earlier role in Drosophila oogenesis than Wisp. (A) Genetic interactions between orb and wisp and between orb and hrg. Females of the indicated genotype were crossed with wild-type males and the embryonic lethality of their progeny was scored. The percentage of embryonic lethality from orb^mel mothers is increased in the presence of both heterozygous wisp or hrg mutants. hrg mutations only are able to dominantly increase the ventralization phenotype of orb^mel. Note that collapsed embryos with normal dorsal appendages is a common phenotype of wisp mutant embryos. This phenotype suggests a defect in vitelline membrane cross-linking, an early event at egg activation. (B) Ovaries of orb^mel single mutant females, or in the presence of wisp^-/+ or hrg^-/+ mutants, visualized with DAPI. Oogenesis progresses normally in orb^mel, wisp⁸⁹/+; orb^mel and wisp⁴⁰/+; orb^mel females, but is blocked at stage 8 in hrg^PAP21/+; orb^mel ovaries. Fifty ovarioles of the indicated genotype were scored and the percentage of abnormal egg chambers arrested at stage 8 is indicated. For stage 8 arrests that were scored in orb^mel or wisp^-/+; orb^mel ovaries, the oocyte was present. (C) Characterization of stage 8 arrest in hrg^PAP21/+; orb^mel ovaries. Immunostaining of ovaries with anti-C(3)G antibody (green) and DAPI (blue), showing the presence of the oocyte in orb^mel and its absence in arrested hrg^PAP21/+; orb^mel egg chambers (arrow). (D) Osk protein accumulation is not affected in wisp mutant oocytes during mid-oogenesis. Immunostaining of wild-type and wisp^KG5287/Df(1)RA47 mutant ovaries with anti-Osk antibody, showing that Osk accumulation at the posterior pole is similar in wild-type and wisp mutant stage 10 oocytes.