Fig. 1. Chromosome condensation requires MAPK activation in mouse spermatocytes. The specific inhibitor U0126, which blocks activation of MAPK signaling, inhibits chromosome condensation during meiotic progression induced by okadaic acid. (A) Control cells; (B) cells treated for 6 hours with 0.5 µM OA, where condensation of chromatin into metaphase is observed; (C) cells preincubated with U0126 for 12 hours are no different from control cells; (D) cells preincubated for 12 hours with 10 µM U0126 before treatment with OA as described above, and in which chromatin condensation was strongly inhibited; cell nuclei were isolated and stained using 5% Giemsa. (E) Immunoblot analysis using anti-phospho-Erks monoclonal antibody (top) or anti-Erks polyclonal antibody (bottom) of protein extracts (30 µg/lane) from cells treated as described in A-D.