Selenium (Se) is an essential trace element for animal and human growth and reproduction. Selenium exerts its biological function mainly through selenoproteins containing selenocysteine (SeCys) encoded specifically by a UGA codon during translation. The function of selenoprotein W (SeW) is related to antioxidation and the expression of this selenoprotein is high in skeletal muscles. Little research has been done on chicken SeW and no chicken SeW DNA sequence has been identified. Thus, this study used reverse transcription-polymerase chain reaction to investigate gene expression of, and the effect of Se on, SeW and the antioxidative enzymes in chickens. Chicken SeW cDNA sequence was identified and confirmed in this study. SeCys is the 13th amino acid residue in the deducted amino acid sequence. Chicken SeW mRNA contains Type II SeCys-insertion sequence (SECIS) to form a stem-loop structure for recognition of UGA as the SeCys codon. Chicken SeW cDNA sequence and the deducted amino acid sequence were compared with other known SeW from seven different species. The results indicate that the homology is 58.5-58.9% in SeW cDNA sequence between chicken and other mammals (human, primate, rat, mouse, sheep and pig) and the homology is only 22.5% in SeW cDNA sequence between chicken and fish. The homology is 54-60% in SeW amino acid sequence between chicken and the others. Nineteen 2-wk-old male Leghorn chickens were assigned randomly into three treatment groups of control (no Se addition), 1 ppm Se addition or 4 ppm Se addition to commercial diets, and the animals was fed Se-supplemented diets for 6 weeks. Se was added to the diet as sodium selenite. The results indicate that the average weight gain was higher in the 1 ppm Se treatment group for the first 4 weeks. The tissue distribution of SeW mRNA was not affected by Se supplementation. The SeW mRNA in kidney was increased by Se treatment, but not in other tissues examined. The tissue distribution for superoxide dismutase (SOD), cellular glutathione peroxidase (cGPX) and catalase (CAT) mRNAs was not affected by Se supplementation. The cGPX appears to be the main enzyme subjected to Se regulation in this study and its activity was increased by Se supplementation. The results from this study showed that Se supplementation with 1 ppm or 4 ppm for 6 weeks increased cGPX activities in chicken skeletal muscle, brain and liver. Therefore, Se supplementation may increase the antioxidative ability in chickens to reduce the possible damage by free radicals in vivo. The results from this study may provide important information contributing to the improvement of antioxidative ability in chickens.
