Comparative renal gene expression in response to abrupt hypoosmotic shock in spotted scat (Scatophagus argus)

Abstract

Scatophagus argus, a euryhaline fish, is notable for its ability to tolerate a wide range of environmental salinities and especially for its tolerance to a rapid, marked reduction in salinity. Therefore, S. argus is a good model for studying the molecular mechanisms mediating abrupt hyperosmoregulation. The serum osmotic pressure decreased steeply within one hour after transferring S. argus from seawater (SW) to freshwater (FW) and remained at new balance throughout the duration of one week. To explain this phenomenon and understand the molecular responses to an abrupt hypoosmotic shock, hypoosmotic stress responsive genes were identified by constructing two suppression subtractive hybridization (SSH) cDNA libraries from the kidneys of S. argus that had been transferred from SW to FW. After trimming and blasting, 52 ESTs were picked out from the subtractive library. Among them, 11 genes were significantly up-regulated (p<0.05). The kinetics studies of gene expression levels were conducted for 1week after the transfer using quantitative real-time PCR. A significant variation in the expression of these genes occurred within 12h after the hypoosmotic shock, except for growth hormone (GH) and polyadenylate binding protein 1 (PBP1), which were significantly up-regulated 2days post-transfer. Our results suggest different functional roles for these genes in response to hypoosmotic stress during the stress response phase (1hpt–12hpt) and stable phase (12hpt–7dpt). Furthermore, the plasma growth hormone level was detected to be significantly elevated at 1hpt and 24hpt following abrupt hypoosmotic shock. Meanwhile, several hematological parameters, hemoglobin (HGB), red blood cell (RBC) and mean cellular hemoglobin concentration (MCHC), were observed to be significantly increased at 12hpt and 2dpt compared with that of control group. Our results provide a solid basis from which to conduct future studies on the osmoregulatory mechanisms in the euryhaline fish.