Female germline expression of OVO transcription factor bridgesDrosophilagenerations

Abstract

AbstractOVO is required for karyotypically female germ cell viability but has no known function in the male germline in Drosophila.ovois autoregulated by two antagonistic isoforms, OVO-A and OVO-B. Allovo-alleles were created as partial revertants of the antimorphicovoD1allele. Creation of new targeted alleles in anovo+background indicated that disrupting the germline-specific exon extension ofovo-Bleads to an arrested egg chamber phenotype, rather than germ cell death. RNA-seq analysis, including >1K full length cDNAs, indicates thatovoutilizes a number of unannotated splice variations in the extended exon and a minor population ofovo-Btranscripts utilizes an alternative splice. This indicates that classicalovoalleles such asovoD1rv23, are not truly null forovo, and are likely to be weak antimorphs. To generate bonafide nulls, we deleted theovo-Aandovo-Bpromoters showing that onlyovo-Bis required for female germ cell viability and there is an early and polyphasic developmental requirement forovo-Bin the female germline. To visualize OVO expression and localization, we endogenously taggedovoand found nuclear OVO in all differentiating female germ cells throughout oogenesis in adults. We also found that OVO is maternally deposited into the embryo, where it showed nuclear localization in newly formed pole cells. Maternal OVO persisted in embryonic germ cells until zygotic OVO expression was detectable, suggesting that there is continuous nuclear OVO expression in the female germline in the transition from one generation to the next.Article Summaryovohas long been considered to be at the top of the female germline sex determination pathway. We utilized updated genetic methods to determine OVO expression, localization, and requirement in the embryonic and adult germline. Our results indicate that OVO is always present, and likely required, in the Drosophila female germline.