Cell Biology

The Importance of Size

Science Signaling  14 Jul 2009:
Vol. 2, Issue 79, pp. ec238
DOI: 10.1126/scisignal.279ec238

Although cell size and cell cycle progression are linked in yeast, it is not clear how, or even if, they are linked in animal cells. Tzur et al. examined the relationship between size, growth rate, and proliferation in lymphoblasts using a mathematical approach to infer cell growth rates from observations of size distributions within asynchronous populations. To avoid potential growth-altering effects of cell cycle inhibitors or other treatments traditionally used to synchronize cell populations, the authors collected newborn cells that were released into the culture medium from proliferating lymphoblasts loosely attached to a nitrocellulose membrane. They found that newborn cells exhibited a brief growth inhibition in early G1 phase and then grew at an exponential rate until they reached a threshold size beyond which their growth rate decreased. When two cells were the same size but different ages, the older cell was more likely to divide first; when two cells were the same age but different sizes, the larger cell was more likely to divide first. Growth and proliferation rates are therefore influenced by both cell size and cell age, implying that proliferation is modulated by both timing and size-measuring sensors. Although this study did not identify biochemical components of the network that communicates cell size information to the machinery that controls growth and cell cycle progression, this mathematical approach may prove useful for further studies aimed at elucidating the signaling circuits that coordinate these processes. A Perspective by Edgar and Kim puts this work into context with other models and discusses how cells might integrate information about size, growth rate, and proliferation.

A. Tzur, R. Kafri, V. S. LeBleu, G. Lahav, M. W. Kirschner, Cell growth and size homeostasis in proliferating animal cells. Science 325, 167–171 (2009). [Abstract] [Full Text]

B. A. Edgar, K. J. Kim, Sizing up the cell. Science 325, 158–159 (2009). [Summary] [Full Text]