Tissue-specific gene signatures of gilthead sea bream (Sparus aurata L.) after hyper- and hypo-osmotic challenges. Sparus aurata

Euryhaline teleosts can live in a wide range of environmental salinities. Transcriptomic analysis in important osmoregulatory and non-osmoregulatory tissues (liver, gills and hypothalamus) by means of a specific oligo-microarray revealed new aspects related to the osmoregulatory processes mediated by different canonical pathways after hypo- or hyper-omotic challenges in gilthead sea bream (Sparus aurata) juveniles. Liver was the most responsive tissue to salinity changes. In addition, around 24 %, 8 % and 12 % of the total genes differentially expressed were affected and regulated in the same way (up- or down-regulated) by both hyper- and hypo-osmotic challenges in liver, gills and hypothalamus, respectively. In liver and gills, functional analysis of the differentially expressed genes established 2 major clusters of canonical pathways related to i) Energy Metabolism and ii) Oxidative Stress: Damage and Repair, whereas for hypothalamus only a main clusters linked to Oxidative Stress: Damage and Repair was identified. Further, this common cluster presents different sub-nodes in all analyzed tissues, with a clear dualism between liver and gills in those pathways involved in nitrogenous turnover, as well as between gills and hypothalamus in cell stress processes. In addition, several sub-nodes related to cell and tissue architecture was only found in hypothalamus. Moreover, only genes involved in xenobiotic metabolism signaling canonical pathway were differentially regulated by both hypo- and/or hyper-salinity transfer in the three tissues considered. Our results indicated that hepatic, branchial and hypothalamic transcriptome of the sea bream clearly responded after 7 days in different environmental salinities, when mainly metabolic and different cell functions are activated to reach homeostasis, or even return to their basal levels. Overall design: Immature males of gilthead sea bream (Sparus aurata L., 80-100 g body mass, n=36) were acclimated for 10 days to experimental control sea water (SW, 38 ‰ salinity, 1049 mOsm·kg−1 H2O osmolality). Fish were randomly distributed in three 400-L tanks in an open system circuit (~ 2.5 kg·m−3 density), under natural photoperiod and constant temperature (18-19 °C). After the acclimation period, the animals were directly transferred, in duplicate, to the following environmental salinities: seawater (SW, 38 ‰ salinity, control group), low salinity water (LSW, 5 ‰ salinity, 139 mOsm·kg−1 H2O osmolality, hypoosmotic environment), and high salinity water (HSW, 55 ‰ salinity, 1439 mOsm·kg−1 H2O osmolality, hyperosmotic environment). On day 7 post-transfer, fish were anesthetized with 2-phenoxyethanol (1 mL·L−1 at the specific salinity water). After blood extraction, hypothalamic lobules and representative samples of liver and gills were dissected.