On exponential or bilinear cell growth during division cycle Stephen Cooper, University of Michigan Medical School 16 May 2006 An alternative view of the problem is presented in a previously published paper (Cooper, S. 2006 Distinguishing between linear and exponential cell growth during the division cycle: Single-cell studies, cell-culture studies, and the object of cell-cycle research. Theoretical Biology and Medical Modeling.http://www.tbiomed.com/content/3/1/10). When comparing the two papers the following points should be noted:First, the Buchwald-Sveiczer paper analyzes the data on only two cells. The previously published paper (Cooper, 2006) pointed out that it is not correct to use the data on only two cells to describe a general rule, particularly when the original data was selected from a larger number of cells. Until a complete presentation of all cells are given, it has been argued (Cooper, 2006) that artifacts in cell growth on a solid surface may give the published results of Buchwald and Sveiczer, To be more precise, it is not argued that the data of Buchwald-Sveiczer is incorrect, but that it is merely the result of two cells and these two cells are not necessarily representative of cell growth of all cells in the culture. Second, Buchwald and Sveizer do not deal with the more important analysis of the biochemical basis for deciding between exponential and bilinear growth. A reading of both papers side-by-side will illuminate the problem.Third, the postulation of gene dosage by Buchwald and Sveiczer is difficult to accept as merely increasing the rate of production of some cell product is not expected to lead to a doubling in the rate of cell growth. For example, if growth is depending on the activity of the protein synthesizing system (ribosomes, tRNAs, RNA polymerases, etc.) it is difficult to know how a doubling in the rate of production of some cell product could lead to a doubling in the rate of protein synthesis. Rather, one would expect, for any gene-dosage model, that there would only be a slow change in the rate of protein synthesis. A similar problem exists if one postulates cell-cycle dependent changes in protein breakdown or turnover.Finally, there is ample experimental evidence supporting exponential growth during the division cycle, and this is summarized by Cooper (2006).It is of interest to note that Buchwald and Sveiczer write that "...the statistical evidence suggesting a bilinear dependence rather than an exponential one is not strong enough to favor one model unequivocally over the other." I strongly agree with this statement. Given the limited set of data (two cells), and the theoretical problems as described in detail by Cooper (2006), I suggest, as I have written previously, that cells grow exponentially during the division cycle. Competing interests There are no competing interests.