Fig. 10. Hypothetical model of the activation of Nek2 and induction of chromatin condensation by Erk1 and p90Rsk2. Erk1 may be activated by local extracellular signals when spermatocytes are mature to enter the meiotic divisions. Activation of Erk1 allows its translocation into the nucleus where it phosphorylates and activates p90Rsk2. Activated Erk1 and p90Rsk2 associates with chromatin, and p90Rsk2 phosphorylates and activates the chromatin-bound Nek2. Activation of Nek2 triggers chromatin condensation into metaphase chromosomes.