Autonomous activation of histone H1 kinase, cortical activity and microtubule organization in one- and two-cell mouse embryos

The activation of M-phase promoting factor (MPF) in one-cell mouse embryo i s independent from the nucleus. Other autonomous phenomena include the cort ical activity observed at the end of the first cell cycle and the reorganiz ation of the microtubule network. Here, we observed that the autonomous con trol of MPF activation is present also in two-cell mouse embryos (H1 kinase activity being higher in the first than in the second cell cycle). Moreove r, the disappearance of the cortical activity in anucleated halves is obser ved when MPF activation takes place. The rounding up of the cytoplast and t he mitotic reorganization of the microtubule network correlates with the ma ximum activity of H1 kinase in anucleated halves from one-cell embryos. In anucleated halves of two-cell stage blastomeres neither the cortical activi ty nor the microtubule reorganization were observed. The degree of activati on of histone H1 kinase, and, as a consequence, the cortical activity and t he microtubule reorganization, does not depend on the distribution of cycli n B. Finally, the level of cyclin B synthesis is similar in anucleated and nucleated halves derived from both one-and two-cell embryos. ((C) Elsevier, Paris).