Pandey, Anupam, Rajesh, Manchi, Baral, Pratibha, Sarma, Debajit, Tripathi, Priyanka H., Akhtar, Md Shahbaz, Ciji, Alexander, Dubey, Maneesh Kumar, Pande, Veena, Sharma, Prakash, and Kamalam, Biju Sam
The objective of this study was to better understand the molecular mechanisms which regulate acclimatory responses and thermal safety margins of rainbow trout (Oncorhynchus mykiss) at temperatures above physiological optimum. For this, we investigated the time course of changes in critical thermal tolerance thresholds and associated hepatic and renal transcript abundance of molecular markers related to cellular stress response, during high temperature acclimation. The experimental fish were initially acclimated to 17 °C and later exposed to a gradually raised elevated temperature regime (22 °C) for a period of 30 days. CT max , CT min and mRNA expression of candidate markers were examined before the thermal challenge (T 0) and over the time-course (days) of high temperature exposure (T 1 , T 3 , T 7 , T 15 and T 30). With respect to organismal response, CT max was significantly elevated at T 3 , but the degree of gain in heat tolerance was not persistent. Contrarily, we observed a gradual loss in cold tolerance with highest CT min estimate at T 30. Based on the time-course of mRNA expression, the studied markers could be categorized into those which were persistently elevated (hsp70a , hsp70b , hspa5 , hsp90a , hsp90b , stip1 and serpinh1 in kidney and hsp90b in liver); those which concurred with changes in CT min (hspbp1 , hsp90b , stip1 , gr1 , hif1a , hyou1 , tnfa and tlr5 in kidney); and those which concurred with changes in CT max (hsp90a , serpinh1 , tlr5 and lmo2 in liver). Apparently, transcriptional changes in kidney and liver reflected CT min and CT max trend, respectively. Expression profile of stip1 and tlr5 suggest that they are potential novel markers which could reflect thermal limits in rainbow trout. Hepatic metabolic markers were either initially elevated (alt , glud , g6pase1) or down-regulated at different time-points (ast2 , gls1 , fas , cpt1b , mtor), linked to gluconeogenesis and metabolic depression, respectively. Whereas, growth-axis markers showed no significant differences. Overall, this time-course analysis has revealed potential associations in organismal and tissue-specific cellular response to high temperature acclimation in a thermally sensitive coldwater ectotherm. • Time-course of high temperature acclimation related changes in CT max , CT min and mRNA expression of stress response markers in kidney and liver was studied over 30 days after gradually shifting the fish from 17 to 22 °C. • The rate of gain in CT max was rapid (peak at day 3) but not persistent, whereas CT min increased gradually and peaked at day 30. • CT min trend concurred with mRNA levels of hspbp1 , hsp90b , stip1 , gr1 , hif1a , hyou1 , tnfa and tlr5 in kidney. • CT max trend concurred with mRNA levels of hsp90a , serpinh1 , tlr5 and lmo2 in liver. • Expression profile of stip1 and tlr5 suggest that they are novel markers of organismal thermal limits in rainbow trout. [ABSTRACT FROM AUTHOR]