Lok D, Jansen M T, de Rooij D G
Cell Tissue Kinet. 1983 Jan;16(1):19-29.
The cell cycle properties of undifferentiated spermatogonia in the Chinese hamster were analysed by the fraction of labelled mitoses technique (FLM) in whole mounted seminiferous tubules. The minimum cell cycle time (Tc) was found to be c. 90 hr for the As and 87 hr for the Apr and Aal spermatogonia, which is appreciably longer than for the differentiating types A2-B2 spermatogonia (60 hr). This is mainly accounted for by a longer tG1. In general the variability in the duration of the cell cycle phases is greater than for differentiating spermatogonia. From the shape and position of the second peak of the FLM curve it could be concluded that the undifferentiated spermatogonia either cycle with a Tc of c. 87-90 hr, or become arrested in G1. This implies that the decrease in proliferative activity of the undifferentiated spermatogonia after stage IV takes place by the arrest of progressively more cells, i.e. by a gradual decrease of the growth fraction, and not by a gradual lengthening of tG1. The arrested cells either differentiate into A1 spermatogonia and divide in stage IX, or remain undifferentiated and are stimulated to enter S again during the following epithelial cycle. It could be deduced from the heights of the second FLM peaks of As and Apr spermatogonia that once triggered into active cycle, the daughter cells of As spermatogonia that became Apr have a greater chance to continue cycling than those that became new As cells.
采用标记有丝分裂分数技术（FLM），对中国仓鼠未分化精原细胞的细胞周期特性进行了分析，分析对象为整装的生精小管。结果发现，As精原细胞的最短细胞周期时间（Tc）约为90小时，Apr和Aal精原细胞的最短细胞周期时间为87小时，这明显长于分化型A2 - B2精原细胞的最短细胞周期时间（60小时）。这主要是由于较长的G1期。一般来说，细胞周期各阶段持续时间的变异性大于分化中的精原细胞。从FLM曲线第二个峰的形状和位置可以得出结论，未分化精原细胞要么以约87 - 90小时的Tc进行循环，要么在G1期停滞。这意味着IV期后未分化精原细胞增殖活性的降低是通过越来越多的细胞停滞实现的，即通过生长分数的逐渐降低，而不是通过G1期的逐渐延长。停滞的细胞要么分化为A1精原细胞并在IX期分裂，要么保持未分化状态，并在随后的上皮周期中被刺激再次进入S期。从As和Apr精原细胞的第二个FLM峰的高度可以推断，一旦进入活跃周期，As精原细胞分化为Apr的子细胞比分化为新的As细胞的子细胞有更大的机会继续循环。
