Ciemerych M A, Kubiak J Z
Institute of Zoology, University of Warsaw, Warsaw, Poland.
Dev Biol. 1998 Aug 15;200(2):198-211. doi: 10.1006/dbio.1998.8930.
Oocytes of wild-type mice are ovulated as the secondary oocytes arrested at metaphase of the second meiotic division. Their fertilization or parthenogenetic activation triggers the completion of the second meiotic division followed by the first embryonic interphase. Oocytes of the LT/Sv strain of mice are ovulated either at the first meiotic metaphase (M I) as primary oocytes or in the second meiotic metaphase (M II) as secondary oocytes. We show here that during in vitro maturation a high proportion of LT/Sv oocytes progresses normally only until metaphase I. In these oocytes MAP kinase activates shortly after histone H1 kinase (MPF) activation and germinal vesicle breakdown. However, MAP kinase activation is slightly earlier than in oocytes from wild-type F1 (CBA/H x C57Bl/10) mice. The first meiotic spindle of these oocytes forms similarly to wild-type oocytes. During aging, however, it increases in size and finally degenerates. In those oocytes which do not remain in metaphase I the extrusion of first polar bodies is highly delayed and starts about 15 h after germinal vesicle breakdown. Most of the oocytes enter interphase directly after first polar body extrusion. Fusion between metaphase I LT/Sv oocytes and wild-type mitotic one-cell embryos results in prolonged M-phase arrest of hybrids in a proportion similar to control LT/Sv oocytes and control hybrids made by fusion of two M I LT/Sv oocytes. This indicates that LT/Sv oocytes develop cytostatic factor during metaphase I. Eventually, anaphase occurs spontaneously and the hybrids extrude the polar body and form pronuclei in a proportion similar as in controls. In hybrids between LT/Sv metaphase I oocytes and wild-type metaphase II oocytes (which contain cytostatic factor) anaphase I proceeds at the time observed in control LT/Sv oocytes and hybrids between two M I LT/Sv oocytes, and is followed by the parthenogenetic activation and formation of interphase nuclei. Also the great majority of hybrids between M I and M II wild-type oocytes undergoes the anaphase but further arrests in a subsequent M-phase. These observations suggest that an internally triggered anaphase I occurs despite the presence of the cytostatic activity both in LT/Sv and wild-type M I oocytes. Anaphase I triggering mechanism must therefore either inactivate or override the CSF activity. The comparison between spontaneous and induced activation of metaphase I LT/Sv oocytes shows that mechanisms involved in anaphase I triggering are altered in these oocytes. Thus, the prolongation of metaphase I in LT/Sv oocytes seems to be determined by delayed anaphase I triggering and not provoked directly by the cytostatic activity.
野生型小鼠的卵母细胞作为停滞于第二次减数分裂中期的次级卵母细胞排卵。它们的受精或孤雌激活会触发第二次减数分裂的完成，随后进入第一次胚胎间期。LT/Sv品系小鼠的卵母细胞以初级卵母细胞的形式在第一次减数分裂中期（MI）排卵，或以次级卵母细胞的形式在第二次减数分裂中期（MII）排卵。我们在此表明，在体外成熟过程中，很大比例的LT/Sv卵母细胞通常仅正常发育至减数分裂中期I。在这些卵母细胞中，丝裂原活化蛋白激酶（MAP激酶）在组蛋白H1激酶（MPF）活化和生发泡破裂后不久被激活。然而，MAP激酶的激活略早于野生型F1（CBA/H×C57Bl/10）小鼠的卵母细胞。这些卵母细胞的第一个减数分裂纺锤体与野生型卵母细胞相似地形成。然而，在老化过程中，它会增大尺寸并最终退化。在那些不滞留在减数分裂中期I的卵母细胞中，第一极体的排出被高度延迟，并且在生发泡破裂后约15小时开始。大多数卵母细胞在第一极体排出后直接进入间期。减数分裂中期I的LT/Sv卵母细胞与野生型有丝分裂单细胞胚胎之间的融合导致杂种细胞在M期延长停滞，其比例与对照LT/Sv卵母细胞以及通过融合两个MI LT/Sv卵母细胞形成的对照杂种细胞相似。这表明LT/Sv卵母细胞在减数分裂中期I期间产生细胞静止因子。最终，后期自发发生，杂种细胞排出极体并形成原核，其比例与对照相似。在LT/Sv减数分裂中期I卵母细胞与野生型减数分裂中期II卵母细胞（含有细胞静止因子）之间的杂种细胞中，后期I在对照LT/Sv卵母细胞以及两个MI LT/Sv卵母细胞之间的杂种细胞中观察到的时间进行，随后是孤雌激活和间期核的形成。同样，大多数MI和MII野生型卵母细胞之间的杂种细胞经历后期，但在随后的M期进一步停滞。这些观察结果表明，尽管LT/Sv和野生型MI卵母细胞中都存在细胞静止活性，但内部触发的后期I仍会发生。因此，后期I触发机制必须要么使CSF活性失活，要么超越CSF活性。减数分裂中期I的LT/Sv卵母细胞自发激活与诱导激活之间的比较表明，这些卵母细胞中参与后期I触发的机制发生了改变。因此，LT/Sv卵母细胞中减数分裂中期I的延长似乎是由后期I触发延迟决定的，而不是直接由细胞静止活性引起的。
