Mechanistic origins of temperature scaling in the early embryonic cell cycle.

Temperature strongly influences physiological and ecological processes, particularly in ectotherms. While complex physiological rates often follow Arrhenius-like scaling, originally formulated for single reactions, the underlying reasons remain unclear. Here, we examine temperature scaling of the early embryonic cell cycle across six ectothermic species, including Xenopus, Danio rerio,  Caenorhabditis, and  Drosophila. We find remarkably consistent apparent activation energies (75  ± 7 kJ/mol), corresponding to a Q of 2.8 at 20°C. Computational modeling shows that both biphasic scaling in key cell cycle components and mismatches in activation energies across partially rate-determining enzymes can explain the observed approximate Arrhenius behavior and its breakdown at temperature extremes. Experimental data from cycling Xenopus extracts and in vitro assays of individual regulators support both mechanisms. These findings provide mechanistic insights into the biochemical basis of temperature sensitivity and the failure of biological processes at thermal limits.