Abstract: ApoC-Ⅰ(Apolipoprotein C-Ⅰ) is the smallest member of the apolipoprotein family, which plays important roles in lipid uptake, secretion and transport. Here, we obtained the full-length cDNA sequence of ayu(Plecoglossus altivelis) ApoC-I gene (PaApoC-Ⅰ) through random sequencing of cDNA library. The cDNA sequence of PaApoC-Ⅰis 574 nucleotides, consisting of a 267 bp open reading frame that encodes a protein of 88 amino acids with a deduced molecular mass of 10.08 ku. The N-terminus of PaApoC-Ⅰcontains a predicted signal peptide of 20 amino acids. Multiple sequence alignment of complete amino acid sequences showed that PaApoC-Ⅰshared the highest amino acid sequence identity (67.0%) with that of rainbow trout (Oncorhynchus mykiss). Phylogenetic tree analysis revealed that ApoC-Ⅰfrom mammals, reptiles, amphibians and fish formed different clusters, and PaApoC-Ⅰfalled into the fish ApoC-Ⅰcluster and was most closely related to that of rainbow trout. Genome structure analysis showed that PaApoC-Ⅰcontained three exons and two introns. Quantitative real-time PCR (qRT-PCR) analysis showed that PaApoC-ⅠmRNA had the highest expressional level in ayu liver. Upon cadmium (Cd) exposure, PaApoC-I transcripts were significantly up-regulated in ayu liver, spleen, kidney and intestine, and were significantly down-regulated in ayu gill. In summary, our present study demonstrated that a tight relationship between the PaApoC-Ⅰ expression and Cd stress, and it can be a potential biomarker for Cd exposure in aquatic organisms. The results would provide the basic data for further studying the function of fish ApoC-Ⅰ and its mechanism in fish response to heavy metal stress.

Key words: Plecoglossus altivelis, ApoC-Ⅰ, sequence analysis, gene expression, cadmium stress