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Archived Comments for: Control and maintenance of mammalian cell size

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  1. Brooks' hypothesis on size control

    Akos Sveiczer, Budapest University of Technology and Economics

    23 February 2005

    Nearly two years ago, Conlon and Raff (J Biol 2003, 2:7) proposed that mammalian cells do not need any checkpoint to maintain size homeostasis. An "evidence" was that cell volume increased linearly, irrespectively of cell size, under an S-phase arrest. Conlon and Raff referred to an old and clever (albeit never proved) hypothesis of Brooks (in The Cell Cycle. Edited by John PCL. Cambridge: Cambridge University Press; 1981), arguing that linearly growing cells not necessarily require any size control mechanism. Last year, Cooper (BMC Cell Biol 2004, 5:35) and we (Sveiczer A, Novak B, Mitchison JM. Theor Biol Med Model 2004, 1:12) criticised the conclusions of Conlon and Raff. We both pointed out that even if S-phase blocked cells grow linearly, it does not mean that these cells normally grow linearly during their cell cycle. In their response to Cooper here (BMC Cell Biol 2004, 5:36), Conlon and Raff state that they had never spoken about linear growth during the normal cycle, because this question had simply never been addressed by them. At the first sight, this is a smart answer to disclaim the criticism, however, it generates a serious problem. Namely, in his old paper Brooks proposed that the cells grew linearly, irrespectively of their size, therefore they increased their volume by the same amount during the cycle, if the cycle time was the same. In that special case, Brooks could suppose even a large scattering in the cycle time, and division size was finally convergent during consecutive cycles, even after a large perturbation. He was definitely thinking of normal cycles, during which the linear rate of growth extension is independent of both size and of cell cycle stage! As a consequence, I think that the answer given here by Conlon and Raff generates an even larger discrepancy and, afterwards, the authors have two possibilities. One of them is to explain in detail how their data and assumptions fulfil the general requirements, where the Brooks' hypothesis might be valid. The other one is to withdraw their conclusions about the lack of size control in mammalian cells.

    Competing interests

    None declared