Genome-wide characterization of three IGFs in hybrid yellow catfish (Pseudobagrus fulvidraco ?x Pseudobagrus vachellii ?) and the association of IGF2 allelic variants with growth traits

"Huangyou No. 1 ", a new hybrid yellow catfish (Pseudobagrus fulvidraco ?x Pseudobagrus vachellii ?) with heterosis in growth traits, is an economically important freshwater fish in China. Among genes related to growth traits, Insulin-like growth factors (IGFs) are recognized as key factors during embryonic development and growth period. Thus, we identified and characterized IGF1, IGF2 and IGF3 gene from hybrid yellow catfish. Phylogenetic analysis showed that the IGF genes were evolutionarily-constrained and their function was conserved. Transcriptional studies indicated that three IGF mRNA expression were most abundant in liver, despite the ubiquitous expression in nine tested tissues. Further, two opposite temporal expression patterns were observed in these three IGF genes during 16 embryogenesis and larval development stages of hybrid yellow catfish, of which IGF2 and IGF3 shared the similar profile highly expressed after gastrula. Finally, single nucleotide polymorphisms (SNPs) of IGF2 were screened and genotyped in 264 hybrid yellow catfish by Sanger sequencing. Only a non-synonymous mutation (SNP 97 T > C) obeyed Hardy-Weinberg equilibrium. Association analysis indicated SNP 97 T > C significantly associated with nine growth traits (body length, full length, head length, body height, caudal peduncle height, caudal peduncle length, body width, body weight and fatness; P < 0.05). This association was also validated in a second population with 183 individuals. Overall, results from our studies highlight the importance of IGF system in mediating growth development of hybrid yellow catfish, and provide a potential marker for "Huangyou No. 1 " breeding.