ABSTRACT
The maternal mRNA Vgl is localized to the vegetal pole during oogenesis in Xenopus. We have cultured oocytes in vitro to begin to understand how this localization occurs. Endogenous Vgl mRNA undergoes localization when oocytes are cultured in vitro, and synthetic Vgl mRNA injected into such oocytes is localized in the same fashion. Vgl mRNA is associated with a detergentinsoluble fraction from homogenized oocytes, suggesting a possible cytoskeletal association. The use of cytoskeletal inhibitors reveals a two-step process for localizing Vgl mRNA. Microtubule inhibitors such as nocodazole and colchicine inhibit the localization of Vgl mRNA in late stage in/early stage IV oocytes, but have no effect on Vgl mRNA once it is localized. The microfilament inhibitor cytochalasin B, however, has little effect on the translocation of Vgl mRNA in middle-stage oocytes but causes a release of the message in late-stage oocytes. We propose a model for the localization of Vgl mRNA in which translocation of the message to the vegetal cortex is achieved via cytoplasmic microtubules and the anchoring of the message at the cortex involves cortical microfilaments.
