Expression of heat shock proteins in anoxic crucian carp (Carassius carassius): support for cold as a preparatory cue for anoxia.

The crucian carp (Carassius carassius) tolerates anoxia for days to months depending on temperature. During episodes of stress, heat shock proteins (HSPs) are important for limiting cellular damage, mainly by ensuring protein function. Accordingly, we hypothesized that anoxia would change the expression of HSPs and that this response would be temperature dependent. Real-time RT-PCR was used to investigate the effects of 1 and 7 days anoxia (A1 and A7) on the expression of HSP70a, HSP70b, HSC70, HSP90, and HSP30 in the brain and heart of 8 degrees C- and 13 degrees C-acclimated crucian carp. In general, the expression of all HSPs changed in response to anoxia, although varying in size and direction, and with organ and temperature. HSP70a expression increased drastically (approximately 10-fold) in A7 brains and hearts at 13 degrees C but not at 8 degrees C. HSC70 and HSP90 expression decreased in A7 brains (by 60-70%), but not in A7 hearts. HSC70 expression increased in A1 brains and hearts at both temperatures (by 60-160%), and HSP30 expression decreased in A7 brains and hearts at both temperatures (by 50-80%). Notably, normoxic fish showed 7- and 11-fold higher HSP70a expression in the brain and heart at 8 degrees C compared with 13 degrees C. This difference disappeared during anoxia, suggesting that cold may function as a cue for preconditioning the crucian carp's HSP70a expression to the approaching anoxic winter period.