Rubin H
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
Proc Natl Acad Sci U S A. 1993 Nov 15;90(22):10715-9. doi: 10.1073/pnas.90.22.10715.
"Spontaneous" neoplastic transformation of cells in culture has been shown to be an adaptive response to moderate physiological constraints such as contact inhibition and lowered concentrations of serum. These are the same constraints that promote normal differentiation of a variety of cell types. Because both normal and neoplastic development represent enduring changes in response to constraint, spontaneous transformation can be considered a form of epigenesis. This phenomenon permits the use of established cell lines in developing general epigenetic principles with all of the advantages of manipulation, efficient cloning, and quantification afforded by such systems. Being environmentally sensitive, however, the responsive capacity of cell lines is subject to fluctuation and long-term modification. I therefore set out to define the conditions used in maintaining cells that influence their competence to undergo transformation with the aim of controlling that competence. It proved to be sensitive to both the population density and frequency of three different repetitive passage regimens. Both the saturation density of the cells and their capacity to produce transformed foci varied initially in different ways within the same regimen in two consecutive passage series starting from the same frozen stock, but both parameters eventually settled down to values characteristic of each of the three regimens. As a result, three sublines were developed of high, intermediate, and low competence for transformation. Each of the sublines has special advantages for studying different aspects of epigenetic change. In the process of developing the sublines, a number of observations were made that reinforce the epigenetic nature of neoplastic transformation and are consistent with the concept of progressive state selection as the basis of the change. That concept can be considered a first step in the formal analysis of epigenesis.
培养中的细胞“自发”肿瘤转化已被证明是对适度生理限制（如接触抑制和血清浓度降低）的一种适应性反应。这些限制与促进多种细胞类型正常分化的限制相同。由于正常发育和肿瘤发育都代表了对限制的持久反应变化，因此自发转化可被视为一种表观遗传形式。这种现象使得在利用既定细胞系发展一般表观遗传原理时，可以利用此类系统所提供的操作、高效克隆和定量等所有优势。然而，由于细胞系对环境敏感，其反应能力会发生波动并受到长期改变。因此，我着手确定维持细胞的条件，这些条件会影响它们发生转化的能力，目的是控制这种能力。结果发现它对三种不同重复传代方案的群体密度和频率都很敏感。从同一冻存细胞株开始的两个连续传代系列中，在同一方案内，细胞的饱和密度及其产生转化灶的能力最初以不同方式变化，但最终这两个参数都稳定在三种方案各自特有的值上。结果，开发出了转化能力高、中、低的三个亚系。每个亚系在研究表观遗传变化的不同方面都有特殊优势。在开发亚系的过程中，进行了一些观察，这些观察强化了肿瘤转化的表观遗传性质，并与渐进状态选择概念一致，该概念是这种变化的基础。该概念可被视为表观遗传学形式分析的第一步。
