Molecular characterization of IGFBP and association analysis with growth traits in the razor clam Sinonovacula constricta

Insulin like growth factor binding protein(IGFBP)is a member of IGFBP family participating in transportation,localization and biological regulation of IGFs.Here,we conducted RACE-PCR and LONG-PCR for the cloning of full length cDNA and DNA of IGFBP gene in Sinonovacula constricta.Quantitative real-time PCR analysis revealed that IGFBP transcript was expressed in a wide range of tissues and developmental stages.Additional growth-linked SNP were discovered based on association study.The full length of IGFBP cDNA sequence consists of 631 base pairs(bp),comprising a 60 bp 5' untranslated region(UTR),a 136-bp 3' UTR,and an open reading frame(ORF)which is 435 bp in length.The ORF encodes 144 amino acids with a signal peptide(18 amino acids)and 12 cysteine residues in the conserve N-terminal.There is one intron(2 687 bp)and two exons(200 and 245 bp)in the sequence of IGFBP gene(3 122 bp).Based on quantitative real-time PCR analysis,we found the highest level of IGFBP expression in the digestive gland.Also the transcript was highly detected in juvenile stages rather than other stages.Four SNPs were identified in IGFBP genomic DNA and one of them was significantly associated with the shell length and body weight.Our results indicated that IGFBP gene plays important roles in the growth and development in S.constricta.