Biochemical and cytological changes associated with expression of deregulated pp60src in Xenopus oocytes

We have examined the effects of Xenopus pp60c-src with constitutive kinase activity on the morphology and maturation of Xenopus laevis oocytes. When RNA encoding this deregulated variant was injected into stage VI oocytes, we observed a gross alteration in the cortex of the oocyte. This alteration involved aggregation of pigment and invagination of the cortex in a large area proximal to the site of injection. This phenomenon was not seen in oocytes injected with RNA encoding wild-type pp60c-src. We have correlated this phenomenon with the tyrosine phosphorylation of 84- and 100-kDa proteins. These phosphorylated proteins colocalized with the alteration in the oocyte cortex when assayed by both biochemical and immunocytochemical methods. Neither the pigment aggregation nor phosphorylation of the 84- and 100-kDa proteins was observed in oocytes expressing a nonmyristoylated version of the deregulated pp60c-src. Expression of deregulated Xenopus fyn, a src-family member, resulted in a phenotype similar to that seen with deregulated src. However, in the fyn-injected oocytes, many more proteins were phosphorylated on tyrosine than in the src-injected oocytes. Progesterone stimulation of oocytes expressing deregulated pp60c-src resulted in an increase in the number of tyrosine-phosphorylated proteins. This change may represent the response of pp60src to the resumption of the cell cycle in maturing oocytes. These data suggest that the oocyte may be a particularly useful system for investigating the role of pp60c-src in the regulation of cytoskeletal structure and in the regulation of events associated with the cell cycle.