Structure and expression of Zebrafish Igf2 and Peg1/Mest

Abstract

Zebrafish genes orthologous to mammalian imprinted genes, Igf2 and Peg1/Mest were characterized in this study. cDNAs of zebrafish Igf2 and Peg1/Mest orthologues, zIgf2 and zPeg1/Mest, were analyzed. Phylogenetic analysis based on amino acid sequence homology indicated that Igf2 and Peg1/Mest are highly conserved among vertebrate species. zIgf2 and zPeg1/Mest potentially encode polypeptides of 198 and 345 amino acids, respectively. Southern hybridization showed that zIgf2 and zPeg1/Mest exist as single copies in the zebrafish genome. Northern hybridization was performed in blastula, segmentation, and larval stages. zIgf2 was expressed in segmentation embryo and in larva, but not in blastula. zPeg1/Mest was expressed in all three stages, exhibiting gradually increased expression as the development proceeds. A polymorphism in 3``-UTR of zIgf2 between AB and EK strains of zebrafish was sought to be exploited as a physically discriminating marker for determination of allelic expression in F1 hybrids. It was found that 3``-UTR of EK strain possesses a polymorphic site. Subsequent investigation of zIgf2 expression pattern revealed that both parental alleles are expressed, suggesting that zIgf2 is not imprinted in zebrafish.