Sub-lethal heat stress causes apoptosis in an Antarctic fish that lacks an inducible heat shock response

• Antarctic fishes possess the lowest upper thermal lethal limit of any known vertebrate.
• In the absence of an inducible heat shock response, sub-lethal heat stress can cause apoptosis.
• The effect of heat on the expression of proliferating cell nuclear antigen is tissue-specific.

The endemic fish fauna of the Southern Ocean are cold-adapted stenotherms and are acutely sensitive to elevated temperature. Many of these species lack a heat shock response and cannot increase the production of heat shock proteins in their tissues. However, some species retain the ability to induce other stress-responsive genes, some of which are involved in cell cycle arrest and apoptosis. Here, the effect of heat on cell cycle stage and its ability to induce apoptosis were tested in thermally stressed hepatocytes from a common Antarctic fish species from McMurdo Sound in the Ross Sea. Levels of proliferating cell nuclear antigen were also measured as a marker of progression through the cell cycle. The results of these studies demonstrate that even sub-lethal heat stress can have deleterious impacts at the cellular level on these environmentally sensitive species.