Quantitative measurements of cell cycle duration and a system-level understanding of a molecular system for cell cycle control

Cells maintain their own size through a round of cell divisions. Since biochemical reactions in a well-mixed solution are independent of the size of the solution, how cell growth and cell division are balanced is a problem in Cell Biology. In Xenopus embryos after Mid-blastula transition (MBT), cell cycle duration elongates in a power law relationship with the cell radius squared. This correlation has been explained by some biochemical activity in proportion to cell surface area. However, it remains unknown whether this second power law hypothesis is valid in other animal embryos. Here, we report the relationship between cell cycle duration and cell size in an invertebrate, Caenorhabditis elegans exhibited a power law distribution (time-volume relationship). The power law relationship was conserved in Xenopus and C. elegans, while the absolute power in C. elegans was different from that in Xenopus. By further studies, we found another power law relationship between nucleus and cell volumes (volume-volume relationship). Interestingly, the power of the volume-volume relationship was almost identical to that of the time-volume relationship. This correlation raised the possibility that the time-volume relationship is explained by the volume ratio of nuclear size and cell size. Thus, our quantitative measurements shed a light on the possibility that early embryonic C. elegans cell cycle duration is coordinated with cell size as a result of geometric constraints between intracellular structures.