Regulation of Expression of the Myo-inositol Monophosphatase 1 Gene in Osmoregulatory Tissues of the European Eel Anguilla anguilla after Seawater Acclimation

Previous microarray studies in our laboratory identified a number of genes that were differentially expressed in "silver" eels after transfer from freshwater (FW) to seawater (SW). A group of genes, which are related to the synthesis, processing, and transport of certain known osmolytes in mammalian cells, have been identified. One gene implicated with osmolyte production is myo-inositol monophosphatase (IMPA1). The aim of this study was to compare the expression of IMPA1 in the major osmoregulatory tissues (intestine, gill, and kidney) as fish move between FW and SW environments. No difference in IMPA1 gene expression was observed in any tissues 6 h after eel transfer to SW; however, after 2 days acclimation, a 1.9- and a 2.5-fold increase in mRNA expression was found in kidney and gill, respectively. These elevated levels were maintained for up to 5 months (4.9- and 3.4-fold, respectively) after SW transfer. No IMPA1 mRNA expression was detected in the intestine. Western blot analysis confirmed the IMPA1 protein was upregulated in the gill, but no changes in protein abundance were detected in the kidney 5 months after SW transfer. Our studies have revealed a potential role for IMPA1 in salinity adaptation in the European eel.