Genome-wide identification of igfbp genes and their different growth expression patterns of mandarin fish

The igfbp family proteins are key regulators of the biological activities of igfs, which play a pivotal role in controlling growth. Growth is highly variable between different fish species and even between growth stages and sexes within the same fish species. For determining the igfbps significantly associated to growth, we identified igfbp genes from the whole-wide genomes of mandarin fish Siniperca chuatsi and big-eye mandarin fish Siniperca kneri, and detected their expression profiles under different growth conditions. The results revealed that: 1) both mandarin fish and big-eye mandarin fish have 10 igfbp family members (igfbp-1a/b, igfbp-2a/b, igfbp-3, igfbp−4, igfbp-5a/b, and igfbp-6a/b), which are highly conserved among igfbp family members; 2) in early development, the expression of igf1 mRNA showed an increasing trend, igfbp-1a/b expression increased significantly with development and the expression trend was strongly similar to that of igf1; 3) variation of body sizes in adult revealed a strong correlation between the serum Gh content and igf1 mRNA expression level in the liver, and the expression levels of hepatic igfbp-2a/b, -4 showed a positive correlation; 4) serum Gh levels and the relative expression of hepatic igf1 mRNA were significantly higher in females than in males, the fold change in igfbp-1a in muscle, -2a, -5a in liver mRNA expression was strongly similar to that of igf1; 5) variation of the interspecific growth showed that the expression of serum Gh and hepatic igf1 mRNA in mandarin fish was significantly higher than that in big-eye mandarin fish. The expression of igfbps mRNA in mandarin fish was significantly higher than that in big-eye mandarin fish, except for igfbp-2a/2b in muscle and igfbp-6a in liver. Taken together, our results suggest that the different effects on growth of mandarin fish are regulated by the actions of different igfbps, where igfbp-1a/b, -2a/b, -4 and -5a may be a candidate for growth rate difference studies. The inherently low expression of Gh, igf1, and igfbps might have contributed to the slow growth of big-eye mandarin fish.