Fig. 4. p90Rsk2 is activated during meiotic G2/M progression induced by okadaic acid. Soluble extracts (500 µg) obtained from either control pachytene spermatocytes or spermatocytes treated for 6 hours with 0.5 µM OA were immunoprecipitated using antibodies specific for the three p90Rsk isoforms. The immunoprecipitated kinase activity was assayed using 10 µM S6 peptide and 10 µM ³²P--ATP as substrates. p90Rsk2 activity was increased 10-fold by incubation of spermatocytes with okadaic acid. Data represent the mean±s.d. of triplicate determinations from three separate experiments.