A phyletic perspective on cell growth.

Commonalities, as well as lineage-specific differences among bacteria, fungi, plants, and animals, are reviewed in the context of (1) the coordination of cell growth, (2) the flow of mass and energy affecting the physiological status of cells, (3) cytoskeletal dynamics during cell division, and (4) the coordination of cell size in multicellular organs and organisms. A comparative approach reveals that similar mechanisms are used to gauge and regulate cell size and proliferation, and shows that these mechanisms share similar modules to measure cell size, cycle status, competence, and number, as well as ploidy levels, nutrient availability, and other variables affecting cell growth. However, this approach also reveals that these modules often use nonhomologous subsystems when viewed at modular or genomic levels; that is, different lineages have evolved functionally analogous, but not genomically homologous, ways of either sensing or regulating cell size and growth, in much the same way that multicellularity has evolved in different lineages using analogous developmental modules.