Temperature-dependent expression of cytochrome-c oxidase in Antarctic and temperate fish

Seasonal acclimation versus permanent adaptation to low temperatures leads to a differential response in the expression of cytochrome-e oxidase (CCO) in temperate and Antarctic eelpouts. Although eurythermal eelpout from the North Sea (Zoarces viviparus) displayed a cold-induced rise of CCO activity in white muscle, enzyme activity in the cold stenothermal Antarctic eelpou t Pachycara brachycephalum failed to reflect such a compensatory increase. In Antarctic eelpout, CCO activity correlates with transcript levels of mit ochondrial encoded subunits of CCO (CCO I and CCO II), whereas cold-acclima ted eelpout from the North Sea show lower enzyme activities than expected o n the basis of mitochondrial mRNA levels. In these animals, CCO expression at low temperatures may be limited either by nuclear CCO transcripts or by posttranscriptional processes. These may comprise translation of the subuni ts or assembly of the CCO holoenzyme. mRNA levels of CCO IV, one of the nuc lear encoded subunits, increased strongly during cold acclimation, indicati ng that the expression of CCO is likely not message limited in cold-acclima ted Z. viviparus. Our data suggest that seasonal cold acclimation of Z. viv iparus results in a modification of the relationship between transcription and translation or posttranslational processes. In permanently cold-adapted P. brachycephalum, on the other hand, CCO expression shows similar charact eristics as in the warm-acclimated confamilial species, e.g., low levels of enzyme activity correlated with low levels of mitochondrial message.