Expression of ras‐like proteins in embryonic and adult cells of Xenopus laevis

Abstract

A polyclonal antibody raised against v-Ha-ras p21 was purified and its specificity was checked on Ha-ras transformed cell lines. It was used to immunoprecipitate p21 from different Xenopus laevis cell types: brain cells, blood cells, and embryonic material. By one-dimensional Western blot analysis, we show that ras p21 is synthesized very early in oogenesis and accumulates throughout vitellogenesis. The ras p21 content, estimated to be 1.1 ng in the full-grown oocyte, remains constant during oocyte maturation and egg cleavage. Increase in the amount of ras p21 occurs at the beginning of neurulation. Two-dimensional Western blot patterns reveal the presence of multiple molecular forms of p21 in all Xenopus cell types studied. The numerous resolved polypeptides were ascribed to the expression of at least two different ras genes. Furthermore, specific charge modifications of the ras polypeptides are observed in brain, blood, and embryonic cells. During oogenesis and early embryonic development, differences in two-dimensional patterns mainly concern variations in the relative amounts of the different polypeptides. The results are discussed in relation to the well documented synthesis activities of the growing oocyte and of the early developing embryo.

Localization of ras proto‐oncogene expression during development in Xenopus Laevis

“…With a homologous probe, we used in situ hybridization to assay for localization of ras transcripts during development. Recent work using heterologous polyclonal antibody has shown ras-like protein expression in embryonic and adult cells in Xenopus laevis (Hanocq-Quertier and Hanocq, 1991). The present study confirms that the Ki-ras mRNA is highly expressed in the cytoplasm of young oocytes and further diluted during oocyte growth without specific localization.…”

“…This observation of a very high level of ras RNA in previtellogenic (stage 1) oocytes could be interpretated as resulting from a specific regulation of ras gene expression. Recent work demonstrated an early appearance of ras p21 protein in previtellogenic Xenopus oocytes, which then accumulates during vitellogenesis (Hanocq-Quertier and Hanocq, 1991). In the young oocytes, the presence of ras mRNA that could be translated into a functional protein from that time favours the hypothesis that ras p21 plays a role in vitellogenesis or in oocyte growth during oogenesis.…”