Characterization and tissue expression of twelve selenoproteins in yellow catfish Pelteobagrus fulvidraco fed diets varying in oxidized fish oil and selenium levels

Selenium (Se) is an essential mineral and plays many crucial physiological functions in the vertebrates, including fish. Dietary Se deficiency and excess adversely influence growth and the metabolism [23], [31]. Se exerts its biological function primarily through the selenoproteins with selenocysteine (Sec). Sec, the 21st amino acid (AA), is encoded by UGA codon. Under the normal condition, the UGA codon performs the stop signal. However, when the 3′ untranslated region (3′UTR) has a specialized stem-loop structure known as a selenocysteine insertion sequence (SECIS), UGA encodes the amino acid Sec [12]. At present, 25 selenoproteins were found in human and 24 selenoproteins in mice [21]. In fish, 18 genes for Sec-containing protein were reported in zebrafish [19] and the cDNA sequences of some selenoproteins were obtained in the other fish, such as Gpx1 in Acrossocheilus fasciatus [26] and southern bluefin tuna Thunnus maccoyii [39], Gpx4 in bluefin tuna T. maccoyii and common carp Cyprinus carpio [11], [39], selenou in Fugu pufferfish [2], selenow in Carassius auratus [3] and selenop in tilapia Oreochromis niloticus [40]. Recently, in our laboratory, the full-length cDNA sequences of seven selenoproteins (such as selenow, selenop, gpx1, gpx3, gpx4, txnrd2 and txnrd3) have been cloned and characterized in yellow catfish and their mRNA expression profiles have been described in various tissues [37].

Fish oil is considered one essential oil source which provides essential fatty acids for fish [41]. However, due to the high un-saturation degree, fish oil is susceptible to oxidation under natural conditions. Oxidized fish oils lead to growth inhibition by activating oxidative stress and dysregulating lipid metabolism [37], [46]. Se plays important roles in improving antioxidant capacity via influencing the expression of selenoproteins [33], [45]. Thus, it is reasonable to hypothesize that dietary Se addition can alleviate the oxidized fish oil-induced oxidative stress via the selenoproteins. However, at present, to our best knowledge, little information is available on the interactive effect of dietary oxidized fish oils and Se on the mRNA expression of these selenoproteins.

Yellow catfish is an important freshwater economic fish with wide culture in China and other Asian countries due to its high economic value. As a part of our many studies involved in the function of selenoproteins for the fish species [43], [45], the study identified the cDNA sequences of twelve selenoproteins (selenoe, selenoh, selenof, selneoi, selenok, selenom, selneon, selenos, selenoo, selenot, selenou and msrb1) genes in yellow catfish. Moreover, their mRNA tissue expression profiles and effects of dietary oxidized fish oils and Se addition on their mRNA expression were determined.

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