Characterization of Insulin-Like Growth Factor Binding Protein 7 (Igfbp7) and Its Potential Involvement in Shell Formation and Metamorphosis of Pacific Abalone, Haliotis discus hannai.

Md Rajib Sharker,Shaharior Hossen,Kang Hee Kho,Ill-Sup Nou

doi:10.3390/ijms21186529

Abstract

Insulin-like growth factor binding proteins (IGFBPs) are secreted proteins that play an important role in IGF regulation of growth and development of vertebrate and invertebrates. In this study, the IGFBP7 gene was cloned and characterized from mantle tissues of H. discus hannai, and designated as Hdh IGFBP7. The full-length cDNA sequence transcribed from the Hdh IGFBP7 gene was 1519-bp long with an open reading frame of 720-bp corresponding to a putative polypeptide of 239 amino acids. The molecular mass of its mature protein was approximately 23.44 KDa with an estimated isoelectric point (pI) of 5.35, and it shared significant homology with IGFBP7 gene of H. madaka. Hdh IGFBP7 has a characteristic IGFBP N-terminal domain (22–89 aa), a kazal-type serine proteinase inhibitor domain (77–128), and an immunoglobulin-like C2 domain (144–223). Furthermore, twelve cysteine residues and a signature motif of IGFBPs (XCGCCXXC) were found in its N-terminal domain. Phylogenetic analysis revealed that Hdh IGFBP7 was aligned with IGFBP7 of H. madaka. Tissue distribution analysis showed that the mRNA of Hdh IGFBP7 was expressed in all examined tissues, with the highest expression level observed in the mantle and gill tissues. The expression level of Hdh IGFBP7 mRNA was relatively higher at the juvenile stage during its metamorphosis period. In situ hybridization showed that Hdh IGFBP7 transcript was expressed in epithelial cells of the dorsal mantle pallial and mucus cells of the branchial epithelium in gill. These results provide basic information for future studies on the role of IGFBP7 in IGF regulation of shell growth, development and metamorphosis of abalone.

Highlights

Insulin-like growth factors are evolutionarily conserved polypeptides that play a critical role in cell growth, proliferation, differentiation, reproduction, and aging in vertebrates and invertebrates [1,2,3,4,5,6]
To explore the functional role of Hdh IGFBP7, we demonstrated the cellular localization of its mRNA by in situ hybridization
The complete coding sequence of IGFBP7 in H. discus hannai was isolated from mantle by 3 -RACE and 5 -RACE PCR and named Hdh IGFBP7

Summary

Introduction

Insulin-like growth factors are evolutionarily conserved polypeptides that play a critical role in cell growth, proliferation, differentiation, reproduction, and aging in vertebrates and invertebrates [1,2,3,4,5,6]. IGFBPs are a family of secreted proteins that contain a highly conserved N-terminal domain, a conserved C-terminal domain, and a variable central linker (L) domain that plays a crucial role in maintaining their structural integrity [11,12]. Such a domain structure is highly conserved among different vertebrate and invertebrate species [13]. Conserved cysteine residues in the N-domain and the C-domain are involved in intradomain disulfide bond formation [15,16] They help to form the globular structure of N- and C-domains. Different forms of IGFBPs share a common domain organization, each IGFBP type, with its unique biochemical properties, possesses stimulatory or inhibitory functions in different IGF-mediated biological activities [17,18]

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