Cell biology. On being the right (cell) size

Abstract

Different animal cell types have distinctive and characteristic sizes. How a particular cell size is specified by differentiation programs and physiology remains one of the fundamental unknowns in cell biology. In this Review, we explore the evidence that individual cells autonomously sense and specify their own size. We discuss possible mechanisms by which size-sensing and size-specification may take place. Last, we explore the physiological implications of size control: Why is it important that particular cell types maintain a particular size? We develop these questions through examination of the current literature and pose the questions that we anticipate will guide this field in the upcoming years.

Figure 1

Sizes of different human cell types. Cells are shown to scale. Pancreatic beta cells (insulin and DNA stained) (76), hepatocytes (β-catenin and DNA stained) (77), keratinocyes from oral tissue (78), fibroblasts (79), adipocytes from subcutaneous tissue (80).

Figure 2

Cell size uniformity in healthy tissues contrasts with cell size heterogeneity in pleomorphic tumors. (A) A section of epidermal stratum spinosum is used to illustrate uniformity in cell size that is typical of epithelial tissues. (B)This uniformity is contrasted with the extreme disparities in cell size in a typical pleomorphic melanoma. Stratum spinosum image was taken from http://www.studyblue.com/ while melanoma section was taken from Pathpedia (http://www.pathpedia.com/).

Figure 3

In populations of proliferating cells, size uniformity may be ensured by linking the processes of growth and cell cycle progression. One way this can be accomplished is by restricting progress through a particular cell cycle stage (for example, the G1/S transition) to cells that have reached a specific “target” size.

Figure 4

To exit G1 with the appropriate size, cells can either adjust the amount of time spent in G1 (A) or the rate at which they grow (B).