7C female sterile mutants fail to accumulate early eggshell proteins necessary for later chorion morphogenesis in Drosophila.

Seven noncomplementing female sterile mutations that affect eggshell assembly in Drosophila have been mapped to the 7C1-3 region of the X-chromosome. TEM of the mature eggshell of one of the alleles, fs(1)410, shows a lack of organization within the endochorion and an accumulation of electron dense material in the vitelline membrane of stage 14 eggchambers. SDS-PAGE of radiolabeled eggshell proteins shows that two proteins, s67 and s85, fail to accumulate in the fs(1)410 eggshell. In wild-type flies s85 is produced during stage 10 of oogenesis and then processed to s67 in stages 13 and 14. Neither s85 nor an additional stage 10 specific follicle cell protein (s130) are detected in fs(1)410 or four of the mutant alleles. Short-term labeling studies, analyses of in vitro translation products, and the simultaneous occurrence of s85 and s130 as electrophoretic variants in geographic fly strains indicate s85 is derived from s130. Although major biochemical differences appear in stage 10, mutant and wild-type eggshells are morphologically indistinguishable until stages 13-14. These results suggest that follicle cell proteins synthesized during the time of vitelline membrane deposition (stage 10) are important for proper assembly of the chorion layers during stages 13 and 14.