Wartenberg H, Hilscher B, Hilscher W
Department of Anatomy, University of Bonn, Germany.
Microsc Res Tech. 1998 Mar 1;40(5):377-97. doi: 10.1002/(SICI)1097-0029(19980301)40:5<377::AID-JEMT5>3.0.CO;2-O.
The aim of this study was the comparison between the mitoses of oogonia and the initial stages of oocyte meiosis. The structural alterations that the germ cell chromatin undergoes during the oogonial mitosis have been compared with those occurring during the G1- and S-phase just before meiosis. Using plastic embedded 1-microm sections of fetal rat ovaries (embryonic days = ED 14-20) labeled with 3H-thymidine and re-embedded for electron microscopy, a study of the structural conditions of the nuclear chromatin has been combined with a kinetic analysis of the oogonial cell cycle and the transitional period into the meiotic prophase. After ovarian differentiation (ED 14) the oogonia show a non-clonal, but strong proliferation. On ED 16, proliferation changes to a clonal pattern and decreases during ED 17. A final increase in 3H-thymidine incorporation on ED 18 characterizes the meiotic S-phase. On ED 19 the nuclear labeling drops to zero. The mitotic cycle of the oogonia lasts 16.5 hr and can be divided into 11 stages according to the concept of El-Alfy and Leblond [(1988) Am. J. Anat., 183:45-56] on the basis of the chromatin pattern. The S-phase (10.0 hours) extends from the telophase-interphase transition through the interphase to early prophase. The postmitotic G1- and S-phases show a more extensive duration, respectively 10 and 11.5 hours, and differ from their oogonial counterparts by the spherical shape of the nuclei from the very beginning. The chromatin pattern is similar until the end of the S-phase and lacks any prophase-like, preleptotenal chromatin condensation before the oocytes exhibit (pre-) leptotenal structures. Once the germ cell has completed a sequence of clonal mitotic divisions, it irrevocably progresses into meiosis. During an extended postmitotic period, the structural characteristics of meiosis emerge stepwise.
本研究的目的是比较卵原细胞的有丝分裂和卵母细胞减数分裂的初始阶段。已将生殖细胞染色质在卵原细胞有丝分裂过程中发生的结构改变与减数分裂前G1期和S期发生的结构改变进行了比较。使用用3H-胸腺嘧啶标记的胎鼠卵巢（胚胎日=ED 14-20）的塑料包埋1微米切片，并重新包埋用于电子显微镜检查，将核染色质的结构状况研究与卵原细胞周期和减数分裂前期过渡期的动力学分析相结合。卵巢分化后（ED 14），卵原细胞表现出非克隆性但强烈的增殖。在ED 16，增殖转变为克隆模式，并在ED 17期间减少。ED 18上3H-胸腺嘧啶掺入的最终增加是减数分裂S期的特征。在ED 19，核标记降至零。根据El-Alfy和Leblond [(1988) Am. J. Anat., 183:45-56]的概念，基于染色质模式，卵原细胞的有丝分裂周期持续16.5小时，可分为11个阶段。S期（10.0小时）从末期-间期转变延伸至间期直至前期早期。有丝分裂后的G1期和S期持续时间更长，分别为10小时和11.5小时，并且从一开始就因其细胞核的球形形状而与其卵原细胞对应物不同。直到S期末染色质模式都相似，并且在卵母细胞呈现（前）细线期结构之前，没有任何类似前期的、前细线期染色质浓缩。一旦生殖细胞完成了一系列克隆性有丝分裂，它就不可逆转地进入减数分裂。在延长的有丝分裂后时期，减数分裂的结构特征逐步出现。
