Department of Zoology, University of California, Berkeley, CA 94720, USA.
Development. 1989 May;106(1):105-18. doi: 10.1242/dev.106.1.105.
When tritiated thymidine triphosphate ([(3)H]TTP) or its immunohistochemically detectable analogue, bromodeoxyuridine triphosphate (BrdUTP), is injected into blastomeres of leech embryos it passes throughout the entire embryo and is rapidly incorporated (within 2 min after injection) into nuclei of cells synthesizing DNA (S phase). In the same embryos a DNA-specific stain can be used to identify cells in mitosis (M phase) or nonreplicative interphase (G(1) or G(2) phase) on the basis of nuclear or chromosomal morphology. Using this procedure, we have determined the lengths and compositions of the mitotic cell cycles of identifiable cells in early embryos of the leech, Helobdella triserialis, and have analysed how the cell cycles change during the first seven stages of development. The relatively short cell cycles of the early blastomeres comprise not only phases of M and S, but also postreplicative gap (G(2)) phases. The lengthening of the cell cycles that occurs as development progresses is primarily accomplished by an increase in the length of G(2) and secondarily by an increase in the length of S and,in some instances, the addition of a prereplicative gap(G(1)) phase; M phase remains relatively constant. These data suggest that the durations of the cell cycles of embryonic cells are regulated by a variety of mechanisms.
当氚标记的胸苷三磷酸 ([（3）H]TTP）或其免疫组织化学可检测的类似物，溴脱氧尿苷三磷酸（BrdUTP），被注射到水蛭胚胎的卵裂球中时，它会传遍整个胚胎，并迅速被合成 DNA 的细胞（S 期）的核吸收。在相同的胚胎中，可以使用一种 DNA 特异性染料来根据核或染色体形态识别有丝分裂（M 期）或非复制间期（G1 或 G2 期）的细胞。使用该程序，我们已经确定了水蛭，Helobdella triserialis，早期胚胎中可识别细胞的有丝分裂细胞周期的长度和组成，并分析了细胞周期在发育的前七个阶段如何变化。早期卵裂球的相对较短的细胞周期不仅包括 M 和 S 期，还包括复制后间隙（G2）期。随着发育的进展，细胞周期的延长主要是通过 G2 期的延长和其次是 S 期的延长来实现的，在某些情况下，还可以添加一个复制前间隙（G1）期；M 期保持相对恒定。这些数据表明，胚胎细胞的细胞周期的持续时间受多种机制的调节。
