Control of cytochrome c oxidase (COX) gene expression in fish in response to temperature

Central to mammalian mitochondrial biogenesis are the transcriptional master regulators PGC‐1α, NRF‐1 and NRF‐2. The role of these factors in coordination of mitochondrial gene expression in lower vertebrates is less clear. We studied the role of these regulators in coordinating COX gene expression in fish that undergo mitochondrial proliferation with cold exposure. Cold acclimation/winter acclimatization increased the expression of some COX subunits more than 20‐fold, whereas other genes are unaffected or even repressed. The best predictors of COX activity were COX5b2 and COX6a. Six species that increased COX biosynthesis in the cold showed no consistent pattern with the expression profiles for the putative master regulators. Increases in COX were not accompanied by increases in PGC‐1α mRNA in five of six species. NRF‐2α mRNA did not change in four of six species. The changes in NRF‐1 mRNA best paralleled changes in COX activity, increasing in three of six species that stimulated COX synthesis in the cold. Our studies are not consistent with a role for the well‐established mammalian master regulators in coordinating the cold‐induced mitochondrial biogenesis in fish muscle. Funded by NSERC Canada (CDM).