Duell E A, Kelsey W H, Voorhees J J
J Invest Dermatol. 1975 Jul;65(1):67-70. doi: 10.1111/1523-1747.ep12598049.
How the constantly renewing epidermis maintains its homeostatic state remains a mystery. A "negative feedback" mechanism of control with chalone, a tissue-specific, species-nonspecific inhibitor of mitosis, has been suggested by Bullough and Laurence. Progress in isolating, purifying, and characterizing epidermal chalone has been slow and difficult because of the lack of a fast, assurate, and meaningful assay system. A G2 assay (depending upon mitotic counts) was used to obtain the data which served as the basis for postulating the existence of chalone. Since a control point with the G1 phase of the cell cycle is considered to be the one with physiologic implications, in vivo and in vitro assays with pure primary epidermal cell cultures have been used to investigate a G1 block. The incorporation of tritiated thymidine into DNA is often used as a measure of the rate of prokiferation. However, inhibition of thymidine transport and phosphorylation have been encountered in several systems and negate this method as an accurate measure of cell proliferation.
不断更新的表皮如何维持其稳态仍属未解之谜。布洛和劳伦斯提出了一种由抑素（一种组织特异性、物种非特异性的有丝分裂抑制剂）进行控制的“负反馈”机制。由于缺乏快速、准确且有意义的检测系统，在表皮抑素的分离、纯化及特性研究方面进展缓慢且困难重重。曾使用一种G2检测法（依据有丝分裂计数）来获取数据，这些数据成为假定抑素存在的基础。由于细胞周期的G1期的一个控制点被认为具有生理学意义，因此已采用纯原代表皮细胞培养物进行体内和体外检测来研究G1期阻滞。将氚标记的胸腺嘧啶核苷掺入DNA常常被用作衡量增殖速率的指标。然而，在多个系统中都遇到了胸腺嘧啶核苷转运和磷酸化受到抑制的情况，这使得该方法无法作为准确衡量细胞增殖的手段。
