David C N, MacWilliams H
Proc Natl Acad Sci U S A. 1978 Feb;75(2):886-90. doi: 10.1073/pnas.75.2.886.
Hydra interstitial stem cells continuously give rise to daughter stem cells as well as precursors for nerve and nematocyte differentiation. Growth of the stem cell population is controlled by the self-renewal probability (Ps): Ps is the fraction of stem cell daughters that remain stem cells in each generation. We have determined Ps for Hydra interstitial stem cells by using a novel technique based on the cell conposition of clones. Stem cell clones were grown in aggregates of nitrogen mustard-inactivated Hydra tissue. They contain several hundred cells after 14 days of growth, including stem cells, differentiating nematocytes, and differentiating nerve cells. Clone size, size variability, and the ratio of differentiating cells to stem cells are sensitive measures of Ps. We have prepared standard curves relating these parameters to Ps, using computer simulations of clone growth. Comparisoon of the experimentally observed parameter of clones to these curves indicates that Ps decreases from 0.8 in 5- to 6-day clones to 0.6 in 10- to 12-day clones. The decrease in Ps coincides with the increase in clone size and suggest that Ps may be regulated by the density of stem cells in clones. Such a mechanism could be responsible for the observed homeostasis of stem cell populations in vivo.
水螅间质干细胞不断产生子代干细胞以及神经和刺细胞分化的前体细胞。干细胞群体的生长由自我更新概率（Ps）控制：Ps是每一代中仍保持为干细胞的干细胞子代的比例。我们通过一种基于克隆细胞组成的新技术确定了水螅间质干细胞的Ps。干细胞克隆在氮芥灭活的水螅组织聚集体中生长。生长14天后，它们包含数百个细胞，包括干细胞、分化中的刺细胞和分化中的神经细胞。克隆大小、大小变异性以及分化细胞与干细胞的比例是Ps的敏感指标。我们使用克隆生长的计算机模拟，制备了将这些参数与Ps相关联的标准曲线。将实验观察到的克隆参数与这些曲线进行比较表明，Ps从5至6天克隆中的0.8降至10至12天克隆中的0.6。Ps的降低与克隆大小的增加相吻合，表明Ps可能受克隆中干细胞密度的调节。这样一种机制可能是体内观察到的干细胞群体稳态的原因。
