ovo, a Drosophila gene required for ovarian development, is specifically expressed in the germline and shares most of its coding sequences with shavenbaby, a gene involved in embryo patterning.

Genetic analyses of Drosophila oogenesis have revealed the central role of ovo, a gene required for differentiation of the female germline. A number of recessive ovo mutations also affect the shavenbaby (svb) function required for late embryo patterning, suggesting a tight structural link between ovo and svb. By using various genomic probes for in situ hybridization to wild type and mutant embryos, we show that ovo indeed shares most of its coding sequences with svb. svb expression is detected early in the presumptive head region and later in each segment. It requires control elements located upstream of the ovo genomic region. ovo expresses abundant maternal RNAs which are uniformly distributed in early cleavage embryos. A fraction that lacks an alternative ovo-specific protein coding region (ORF 2b) is detected in pole cells. Expression of an ovo-specific lacZ reporter gene (ovoB) shows that ovo encodes a nuclear protein present in the germline of both sexes. Zygotic ovoB expression is first detected in embryos at around stage 17 and persists up to the adult stage. Our data show that the germline specific expression of ovo in females correlates with its function in oogenesis. This expression, however, is also observed in males in which ovo is not required.