Masui Y, Lohka M J, Shibuya E K
Symp Soc Exp Biol. 1984;38:45-66.
Fully grown amphibian oocytes are arrested at the diplotene stage of meiosis. When they undergo meiotic maturation, meiosis resumes and the oocyte chromosomes condense to metaphase. During this period, the oocyte cytoplasm develops 'chromosome condensation activity' (CCA), the ability to induce the formation of metaphase chromosomes from nuclei transplanted into the oocytes. The cytoplasm also produces 'maturation promoting factor' (MPF), the substance that induces meiotic maturation when injected into oocytes. Also, before meiosis is arrested again at the 2nd metaphase, the cytoplasm develops 'cytostatic factor' (CSF), the substance that causes metaphase arrest when injected into zygotes. Since CSF-arrested zygotes have properties similar to those of metaphase-arrested oocytes, including the potential to resume cell cycle activities, CSF appears to be a genuine factor that causes meiotic arrest. Following oocyte activation, meiosis is completed and the chromosomes decondense to form a pronucleus. During this period, the oocyte cytoplasm loses its CCA and develops 'chromosome decondensation activity' (CDA), the ability to decondense the chromatin of injected nuclei. Concomitantly, MPF and CSF disappear. Both MPF and CSF are inactivated by Ca2+ ions, in vitro. The sensitivity of CCA to Ca2+ and the requirement for Ca2+ during the development of CDA have also been demonstrated in vitro by incubating demembranated sperm nuclei in cell-free preparations from unactivated or activated oocytes. Preparations made from unactivated oocytes in the presence of EGTA exhibit CCA, whereas those made in the absence of EGTA, as well as those made from activated eggs, exhibit CDA. Unactivated ooplasmic preparations made using EGTA lose CCA and develop CDA when Ca2+ ions are added to them. However, at low Ca2+ concentrations CCA is sustained and, when unactivated and activated preparations are mixed, is able to overcome CDA. Therefore, it is likely that at low intracellular Ca2+ levels in unactivated oocytes, CSF is stable and CCA predominates over CDA, thus preventing oocyte chromosomes from decondensing. However, when Ca2+ levels are elevated during oocyte activation, CSF disappears and CCA is replaced by CDA. This change in cytoplasmic activities may allow meiosis to resume.
完全成熟的两栖类卵母细胞停滞于减数分裂的双线期。当它们进行减数分裂成熟时，减数分裂重新开始，卵母细胞染色体浓缩至中期。在此期间，卵母细胞细胞质产生“染色体浓缩活性”（CCA），即诱导移植到卵母细胞中的细胞核形成中期染色体的能力。细胞质还产生“成熟促进因子”（MPF），将其注入卵母细胞时可诱导减数分裂成熟。此外，在减数分裂再次停滞于第二次中期之前，细胞质产生“细胞静止因子”（CSF），将其注入受精卵时可导致中期停滞。由于CSF停滞的受精卵具有与中期停滞的卵母细胞相似的特性，包括恢复细胞周期活动的潜力，CSF似乎是导致减数分裂停滞的真正因子。卵母细胞激活后，减数分裂完成，染色体解聚形成原核。在此期间，卵母细胞细胞质失去其CCA并产生“染色体解聚活性”（CDA），即解聚注入细胞核染色质的能力。同时，MPF和CSF消失。在体外，MPF和CSF都被Ca2+离子灭活。通过在未激活或激活的卵母细胞的无细胞制剂中孵育去膜精子核，也在体外证明了CCA对Ca2+的敏感性以及CDA发育过程中对Ca2+的需求。在EGTA存在下由未激活的卵母细胞制成的制剂表现出CCA，而在没有EGTA的情况下制成的制剂以及由激活的卵制成的制剂表现出CDA。使用EGTA制备的未激活卵质制剂在添加Ca2+离子时会失去CCA并产生CDA。然而，在低Ca2+浓度下，CCA得以维持，并且当未激活和激活的制剂混合时，能够克服CDA。因此，在未激活的卵母细胞中，细胞内Ca2+水平较低时，CSF可能是稳定的，CCA比CDA占优势，从而防止卵母细胞染色体解聚。然而，当卵母细胞激活期间Ca2+水平升高时，CSF消失，CCA被CDA取代。细胞质活动的这种变化可能使减数分裂得以重新开始。
