4 Coordination of Cell Growth and Cell Division

Abstract

Mechanisms regulating cellular reproduction are the core problems in the life sciences. Virchow observed, “Omnis cellula a cellula” (Virchow 1858). A single cell is a package of heritable information coupled with the resources needed to duplicate that information. Boveri early observed that the size of the nucleus, which we now know contains the cell’s heritable information, does not change after reproduction (Boveri 1905). Julius Sachs further showed that the ratio of cytoplasm to nucleus varied little among cells (Sachs 1898). It is probable that the physics of surface tension sets a limit on the potential sizes of cells within a range of possible cell sizes (Thompson 1961). In contrast, limitations on the content of genetic information are likely based on subtler evolutionary parameters because so much DNA is non-coding. Nevertheless, although total cellular DNA content varies by more than five orders of magnitude among all eukaryotes (Gregory 2001), the ratio of cell size to DNA content can be linear across like species; DNA content in the nucleated erythrocytes of a cohort of closely related mammalian species is an intriguing example of this potential linearity (Gregory 2000). It therefore seems likely that evolutionary selection of optimal cellular DNA content adheres to testable physiologic rules.

Early studies of the question of how cell growth is coordinated with cell division to keep a balance between heritable information and cellular resources were obviously limited by the histologic techniques of the time. The next step in these studies required the identification of DNA as the...