Different roles for the adjoining and structurally similar A-rich and poly(A) domains of oskar mRNA: Only the A-rich domain is required for oskar noncoding RNA function, which includes MTOC positioning

Origin and establishment of the germline in Drosophila melanogaster

The continuity of a species depends on germ cells. Germ cells are different from all the other cell types of the body (somatic cells) as they are solely destined to develop into gametes (sperm or egg) to create the next generation. In this review, we will touch on 4 areas of embryonic germ cell development in Drosophila melanogaster: the assembly and function of germplasm, which houses the determinants for germ cell specification and fate and the mitochondria of the next generation; the process of pole cell formation, which will give rise to primordial germ cells (PGCs); the specification of pole cells toward the PGC fate; and finally, the migration of PGCs to the somatic gonadal precursors, where they, together with somatic gonadal precursors, form the embryonic testis and ovary.

Knock down analysis reveals critical phases for specific oskar noncoding RNA functions during Drosophila oogenesis

The oskar transcript, acting as a noncoding RNA, contributes to a diverse set of pathways in the Drosophila ovary, including karyosome formation, positioning of the microtubule organizing center (MTOC), integrity of certain ribonucleoprotein particles, control of nurse cell divisions, restriction of several proteins to the germline, and progression through oogenesis. How oskar mRNA acts to perform these functions remains unclear. Here, we use a knock down approach to identify the critical phases when oskar is required for three of these functions. The existing transgenic shRNA for removal of oskar mRNA in the germline targets a sequence overlapping a regulatory site bound by Bruno1 protein to confer translational repression, and was ineffective during oogenesis. Novel transgenic shRNAs targeting other sites were effective at strongly reducing oskar mRNA levels and reproducing phenotypes associated with the absence of the mRNA. Using GAL4 drivers active at different developmental stages of oogenesis, we found that early loss of oskar mRNA reproduced defects in karyosome formation and positioning of the MTOC, but not arrest of oogenesis. Loss of oskar mRNA at later stages was required to prevent progression through oogenesis. The noncoding function of oskar mRNA is thus required for more than a single event.