Transcriptional responses of the black-chinned tilapia Sarotherodon melanotheron to salinity extremes

摘要

Sarotherodon melanotheron is one of the most euryhaline teleosts able to withstand variations inenvironmental salinity ranging from freshwater (FW) to 130%o hyper-saline waters (HSW). Althoughsignificant progress has been made in exploring the cellular and molecular changes that accompany salinityadaptation in teleosts, little is known about the effects of long-term acclimation to HSW. We sought toidentify in this tilapia species the genes whose transcription is induced by long-term acclimation either toHSW or FW. Two subtractive cDNA libraries were made from gills of fish acclimated for 45 days to eithercondition, with 320 partial cDNA sequences encoding proteins potentially involved in the response to thetwo salinity extremes. The ESTs comparisons with genomic databases allowed putative functions to beattributed to 197 of these genes. The suppression subtractive hybridisation (SSH) results were validated byReal-time PCR for 13 candidate genes having presumably a role in osmoregulation, supplemented by Na', r-ATPase a-subunit and carbonic anhydrase, two genes known to be implicated in this function. In fishacclimated to both salinity extremes, the functional category of cellular process was the predominant one,which may indicate high cellular turnover rates in FW and HSW-adapted fish. The acclimation to FW andHSW also appeared to trigger the expression of genes involved in transport activity, biological regulation andmetabolic processes, at a higher level in fish acclimated to HSW, suggesting higher metabolic activity in thissituation. These results are a first step towards the identification of key molecular processes involved in thefish acclimation to extreme salinities.