Lost in translation? Evidence for a muted proteomic response to thermal stress in a stenothermal Antarctic fish and possible evolutionary mechanisms

Stenothermal Antarctic notothenioid fishes are noteworthy for their history of isolation in extreme cold and their corresponding lack of the canonical heat shock response. Despite extensive transcriptomic studies, the mechanistic basis for stenothermy has not been fully elucidated. Given that the proteome better represents an organism's physiology, the possibility exists that some aspects of stenothermy arise posttranscriptionally. Here, Antarctic emerald rockcod (<i>Trematomus bernacchii</i>) were sampled after exposure to chronic and/or acute high temperatures, followed by a thorough assessment of proteomic responses in the brain, gill, and kidney. Few cellular stress response proteins were induced, and overall responses were modest in terms of the numbers of differentially expressed proteins and their fold changes. Inconsistencies in protein induction across treatments and tissues are suggestive of dysregulation, rather than an adaptive response. Changes in regulation of the translational machinery in Antarctic notothenioids could explain these patterns. Some components of translational regulatory pathways are highly conserved [e.g., Ser-52, eukaryotic translation initiation factor 2α (eIF2α)], but other proteins comprising the cellular "integrated stress response," specifically, the eIF2α kinases general control nonderepressible 2 (GCN2) and PKR-like endoplasmic reticulum kinase (PERK), may have evolved along different trajectories in Antarctic fishes. Taken together, these observations suggest a novel hypothesis for stenothermy and the absence of a coordinated cellular stress response in Antarctic fishes.<b>NEW & NOTEWORTHY</b> Antarctic fishes have some of the lowest known heat tolerances among vertebrates, but the molecular mechanisms underlying this pattern are not fully understood. By combining detailed analyses of protein expression patterns in several tissues under various heat treatments with a broader evolutionary perspective, this study offers a novel hypothesis to explain the narrow range of temperature tolerance in this extraordinary group of fishes.