Molecular characterization and tissue distribution of Frizzled (FZD) in yellow catfish (Pelteobagrus fulvidraco) by copper exposure

Four complete FZD cDNA sequences, designated fzd2, fzd3a, fzd4 and fzd10, were amplified by RT-PCR and RACE approaches from Pelteobagrus fulvidraco. The validated cDNAs encoding for fzd2, fzd3a, fzd4 and fzd10 were 2 176, 3 243, 2 509 and 3 021 bp in length, encoding peptides of 551, 695, 550 and 586 amino acid residues, respectively. The amino acid alignment and phylogenetic analysis revealed that Fzd sequences were relatively conserved among different vertebrates, and fzds of P. fulvidraco were more closely related to those of Ictalurus punctatus. All fzds mRNAs were expressed in all tested tissues (brain, spleen, kidney, gill, heart, muscle, mesenteric fat, liver and ovary), but at variable levels. On day 28, fzd3a mRNA levels increased with increasing waterborne Cu concentration, but mRNA expression showed no significant differences among the three groups. On day 56, fzd2 mRNA levels were the highest in 30 μg Cu/L group and showed no significant differences between other two groups, and mRNA levels of fzd3a, fzd4 and fzd10 showed no significant differences among three groups. The present study will be helpful to understanding the physiological functions of fzd genes.