Fig. 4. Wee1 is tyrosine phosphorylated at the MBT and gastrulation. (A) Lysates prepared from stage VI oocytes (oocyte), eggs arrested at metaphase of meiosis II (egg), embryos in the first mitotic cell cycle (egg 30 minutes), cleavage stage embryos (stage 7 and 8) and embryos after the MBT (stage 9), the early gastrula stage (stage 10), and at mid-gastrula stage (stage 11.5) were examined by immunoblot analysis using antibodies recognizing Wee1, Cdc25A, Cdc25C, phospho-Cdc2 and total Cdc2. One oocyte or embryo equivalent was loaded per lane. Tyrosine-phosphorylated Wee1 was detected by probing Wee1 immunoprecipitates with anti-phosphotyrosine antibody. (B) Depicted are developmental expression profiles of members of the Wee1 kinase and Cdc25 phosphatase families and the developmentally regulated tyrosine phosphorylation (pY) of Cdc2 and Wee1.