Albers K M, Greif F, Setzer R W, Taichman L B
Department of Oral Biology and Pathology, School of Dental Medicine, State University of New York, Stony Brook 11794.
Differentiation. 1987;34(3):236-40. doi: 10.1111/j.1432-0436.1987.tb00071.x.
Cell-cycle withdrawal is the irreversible arrest of replication that occurs in keratinocytes early in terminal differentiation. According to the epidermal proliferation unit (EPU) model of renewal, withdrawal takes place in a subset of cells that have completed a final cycle of amplification replication. Using a recently developed double-labelling assay, we followed cell-cycle withdrawal in growing cultures of epidermal keratinocytes and correlated these results with population-growth kinetics. The levels of withdrawal measured were much too high to be consistent with the population-growth kinetics. These unexpectedly high levels could be explained by postulating that withdrawal takes place in a specific subset of cells, as described by the EPU model. Other possible explanations were entertained but, for various reasons, were considered unlikely. To learn whether withdrawal occurred in basal or suprabasal cells, confluent cultures were pulse labeled with 3H-thymidine, and the position of the labeled cells was monitored by autoradiography during the period of cold chase. The results indicated that, in cultured keratinocytes, withdrawal takes place while the cells are still in the basal compartment.
细胞周期退出是指角质形成细胞在终末分化早期发生的不可逆复制停滞。根据表皮更新的表皮增殖单位（EPU）模型，退出发生在完成最后一轮扩增复制的细胞亚群中。我们使用最近开发的双标记检测方法，追踪了表皮角质形成细胞生长培养物中的细胞周期退出情况，并将这些结果与群体生长动力学相关联。所测得的退出水平过高，与群体生长动力学不一致。这些出乎意料的高水平可以通过假设退出发生在特定的细胞亚群中来解释，正如EPU模型所描述的那样。我们考虑了其他可能的解释，但由于各种原因，认为这些解释不太可能。为了了解退出是发生在基底细胞还是基底上层细胞中，我们用³H-胸腺嘧啶对汇合培养物进行脉冲标记，并在冷追踪期间通过放射自显影监测标记细胞的位置。结果表明，在培养的角质形成细胞中，退出发生在细胞仍处于基底层时。
