Expression and characterization of nonmammalian selenoprotein P in the zebrafish, Danio rerio

Background: Selenoprotein P is a protein of considerable intrigue due to it s unusual composition and requirements for its biosynthesis. Whereas most s elenoproteins contain a single selenocysteine residue, the human, bovine an d rodent selenoprotein P genes encode proteins containing 10-12 selenocyste ines. Selenoprotein P genes have, to date, only been reported in mammals, a nd the function of the protein remains elusive. Results: Herein, we report the identification and characterization of nonma mmalian selenoprotein P in the zebrafish Danio rerio. Sequencing of the cDN A revealed the presence of 17 selenocysteine codons, the highest number rep orted in any protein. Two histidine-rich regions present in the mammalian s elenoprotein P sequences are conserved in the zebrafish protein, and two SE CIS elements are present in the 3' untranslated region. Whole-mount in situ hybridization of zebrafish embryos revealed high levels of expression of s elenoprotein P mRNA in fertilized eggs and in the yolk sac of developing em bryos. Transient transfection of the cDNA in mammalian cells resulted in ef ficient expression of the full-length secreted selenoprotein. A single N-gl ycosylation site is predicted, and shown to be utilized. Conclusions: Discovery of selenoprotein P in the zebrafish opens a previous ly unavailable avenue for genetic investigation of the functions of this un usual protein.