Transcriptional coactivator p15 (PC4) encodes an effectively diverse protein with highly conserved structure and performs critical functions in RNA polymerase II -mediated transcription, DNA replication and damage repair. Although comprehensive investigations of PC4 have been characterized in most vertebrates and some invertebrates, the crucial roles of PC4 were less systematically validated in bivalve mollusks. In the present study, the function of PC4, particularly Arg0230340.1 which had been identified to be highly associated to thermotolerance, in bay scallops Argopecten irradians irradians (AiPC4s) was verified through suppression of Arg0230340.1 expression with dsRNA-mediated RNAi (5 mu M, 10 mu M and 20 mu M). Then, expression regulations of AiPC4s in temperature sensitive tissues (heart, mantle and gill) and cardiac performance including resting heart rate (RHR), maximum heart rate (HRmax) and Arrhenius break temperature (ABT) of bay scallops were detected 24 h after injection of siRNA. After interference, Arg0230340.1 displayed an obvious decrease in experimental groups (5 mu M, 10 mu M and 20 mu M) relative to that in control (NG) and blank groups (DG). Simultaneously, the suppression of Arg0230340.1 expression resulted in a significant decrease of HRmax in experimental groups, but with no marked differences for RHR among groups. Importantly, the suppression of Arg0230340.1 significantly weakened the thermotolerance of bay scallops, as proven by a reduction up to 4.09 degrees C of ABT in experimental groups (5 mu M-28.09 +/- 1.46 degrees C, 10 mu M-27.33 +/- 0.09 degrees C, 20 mu M-27.31 +/- 0.21 degrees C) than that in NG (31.60 +/- 0.05 degrees C)/DG (31.73 +/- 0.01 degrees C). Interestingly, the suppression of Arg0230340.1 resulted in functional compensation and cross -regulation among AiPC4 family members, displaying a tissue -specific expression regulation profile. Moreover, contributions of AiPC4s to thermotolerance in bay scallops suggested that Arg0230340.1 displayed a dominating contribution to ABT in heart (58.47%) and mantle (48.32%), whereas Arg0159040.1 contributed to the highest degree (59.25%) in gill. This work verified the leading role of Arg0230340.1 and its diverse interaction with other AiPC4s in thermotolerance of bay scallops, providing clues for elucidating the tissue -specific regulation of compensation effect of AiPC4s and proving the feasibility of AiPC4s as a candidate gene for the breeding of thermal -tolerant scallops.
