Genetic and molecular analysis of an eggshell mutant in Drosophila melanogaster

The eggshell in Drosophila is produced by ovarian follicle cells during the late stages of oogenesis (stages 9-14). Eggshell formation involves the ordered synthesis and assembly of several protein components. Genes encoding the most abundant eggshell proteins have been identified by molecular cloning studies. Morphological examination of eggs produced by females carrying female sterile mutation on the X and the third chromosome have revealed additional genetic loci involved in chorion formation. In this study I screened a collection of female sterile mutants carrying EMS induced mutations on the second chromosome for eggshell mutants. A class of six mutants with potential vitelline membrane defects was identified based on the response of the mutant eggs to hypochorite solution. Biochemical analysis showed that one mutant, fs(2) QJ42, failed to produce a major vitelline membrane protein, sV23. The mutation was cytogenetically mapped to a previously identified vitelline membrane gene region 26A on the second chromosome. Northern blot analysis using the cloned copy of the sV23 gene as a probe showed accumulation of complementary RNA in the mutant at a 20 fold reduced level relative to wild type. sV23 synthesis and fertility was restored in the mutant when a normal copy of the sV23 gene was introduced into the mutant via germ line transformations. These results suggest a direct relationship between lack of the protein and female sterility in the mutant. To define the mutant functional genetic unit, 5$\sp\prime$-flanking DNA deletion studies were carried out. Transformation experiments showed that 147 bp of 5$\sp\prime$-flanking DNA was enough for proper temporal expression of sV23 as well as restoration of fertility in fs(2) QJ42