Novel roles of the proteins Oskar and Bluestreak in germ cell formation and migration

by 1978- Jones, Jennifer Rebecca

Germ cell formation in Drosophila relies on polar granules, large ribonucleoprotein complexes found at the posterior end of the embryo. The granules undergo characteristic changes in morphology during development, including the assembly of multiple spherical bodies from smaller precursors. Several polar granule components, both protein and RNA, have been identified. One of these, Oskar protein, acts to initiate granule formation during oogenesis and to recruit other granule components. To ask if Oskar has a continuing role in the organization of the granules and control of their morphology, we took advantage of species-specific differences in polar granule structure. The polar granules of D. immigrans fuse into a single large oblong aggregate, as opposed to the multiple distinct spherical granules of D. melanogaster embryos. We cloned the D. immigrans oskar gene and expressed it in D. melanogaster embryos. D. immigrans oskar not only rescues the body patterning and pole cell defects of embryos from D. melanogaster oskar- mothers, but also converts the morphology of the polar granules to that of D. immigrans. The nuclear bodies, structures which appear to be closely related to polar granules, are also converted to the D. immigrans type morphology. We conclude that oskar plays a persistent role in the polar granules, first initiating their formation and later controlling their organization and morphology.