Genetic Evidence That the Ovo Locus Is Involved in Drosophila Germ Line Sex Determination

Zygotically contributed ovo gene product is required for the survival of female germ cells in Drosophila melanogaster. Trans-allelic combinations of weak and dominant ovo mutations (ovoD) result in viable germ cells that appear to be partially transformed from female to male sexual identity. The ovoD2 mutation is partially suppressed by many Sex-lethal alleles that affect the soma, while those that affect only the germ line fail to interact with ovoD2. One of two loss-of-function ovo alleles is suppressed by a loss-of-function Sex-lethal allele. Because ovo mutations are germ line dependent, it is likely that ovo is suppressed by way of communication between the somatic and germ lines. A loss-of-function allele of ovo is epistatic to germ line dependent mutations in Sex-lethal. The germ line dependent sex determination mutation, sans fille, and ovoD mutations show a dominant synergistic interaction resulting in partial transformation of germ line sexual identity. The ovo locus appears to be involved in germ line sex determination and is linked in some manner to sex determination in the soma.     

Gonadal Dysgenesis Reveals Sexual Dimorphism in the Embryonic Germline of Drosophila

In hybrid dysgenesis, sterility can occur in both males and females. At 27.5 degrees, however, we found that P element-induced germline death was restricted to females. This sex-specific gonadal dysgenesis (GD) is complete by the first larval instar stage. As such, GD at 27.5 degrees reveals the sexually dimorphic character of the embryonic germline. The only other known dimorphic trait of the embryonic germline is the requirement for ovo. ovo is required for germline development in females only and has been implicated in germline sex determination. Dominant mutations of ovo partially suppressed female GD. Although embryonic germ cells are undifferentiated and morphologically indistinguishable between males and females, the functional dimorphism seen in ovo requirement and GD at 27.5 degrees indicates that sexual identity in Drosophila germ cells is established in embryogenesis.     

Developmental Analysis of the Ovarian Tumor Gene during Drosophila Oogenesis

Severe alleles of the ovarian tumor (otu) and ovo genes result in female sterility in Drosophila melanogaster, producing adult ovaries that completely lack egg chambers. We examined the developmental stage in which the agametic phenotype first becomes apparent. Germ cell development in embryos was studied using a strategy that allowed simultaneous labeling of pole cells with the determination of embryonic genotype. We found that ovo(-) or otu(-) XX embryonic germ cells were indistinguishable in number and morphology from those present in wild-type siblings. The effects of the mutations were not consistently manifested in the female germline until pupariation, and there was no evidence that either gene was required for germ cell viability at earlier stages of development. The requirement for otu function in the pupal and adult ovary is supported by temperature-shift experiments using a heat-inducible otu gene construct. We demonstrate that otu activity limited to prepupal stages was not sufficient to support oogenesis, while induction during the pupal and adult periods caused suppression of the otu mutant phenotype.