大菱鲆类胰岛素生长因子3基因的克隆和表达分析

Cloning and expression analysis of IGF3 in turbot (Scophthalmus maximus)

中文关键词: 大菱鲆  IGF3  基因克隆  组织表达  卵巢发育

英文关键词: Turbot Scophthalmus maximus  IGF3  Gene cloning  Tissue expression  Ovarian development

中文摘要:

      类胰岛素生长因子3 (insulin-like growth factor 3, IGF3)在硬骨鱼类性别分化过程中扮演重要角色，但其是否影响卵巢发育尚不明确。本研究以欧亚养殖良种大菱鲆(Scophthalmus maximus)为实验材料，通过RACE (rapid-amplification of cDNA ends)克隆技术，获得了IGF3全长cDNA序列，分析了其生物信息学特征，预测了其与IGF特异性受体(IGF receptors, IGF-1R, IGF-2R)结合情况，查明了其组织和卵巢不同发育时期表达规律。结果显示，大菱鲆IGF3 cDNA全长为1 255 bp，编码259个氨基酸。生物信息学分析发现，IGF3为亲水性蛋白，具有典型的IGF特异性结构域和信号肽序列，同狭鳞庸鲽(Hippoglossus stenolepis)同源性最高；蛋白质三级结构域由3个α螺旋串联而成，同IGF-1R和IGF-2R紧密结合。组织表达分析显示，igf3在大菱鲆各个组织中均有分布，雌、雄大菱鲆表达规律显著不同，但皆在脑组织中表达最高。在卵巢发育过程中，igf3在卵黄生成后期表达量显著上升，在核迁移期达到最高，在闭锁期显著下降。以上结果表明，大菱鲆IGF3具有典型的IGFs家族结构特征，作为局域性内分泌因子，在组织中广泛分布且具有显著的性别二态性，同时参与调控了卵巢发育和成熟。相关结果为深入解析IGF3对大菱鲆卵巢发育和卵母细胞成熟的影响及其作用机制奠定了基础，也为探究鱼类IGF3新功能提供了重要思路。

英文摘要:

      The insulin-like growth factor (IGF) system plays a key regulatory role in biological processes, such as growth, reproduction, early development, cell differentiation, and proliferation, in fish and other vertebrates. The IGF family system consists of two IGFs (IGF1 and IGF2), two IGF receptors (IGF-1R and IGF-2R), and six IGF-binding proteins (IGF-binding proteins IGFBP1–6) in mammals. By binding to the cell surface-specific receptor (IGF-Rs), IGFs activate the activity of related protein kinases, initiate the signaling cascade in the cell, and participate in the regulation of various biological reaction processes. The research on fish IGFs mainly focuses on IGF1 and IGF2, and several studies have confirmed that they are widely involved in multiple biological processes, such as growth regulation, immune response, gonadal development, and maturation. IGF3 is a fish-specific sub-type; it was first detected in zebrafish (Danio rerio) and Nile tilapia (Oreochromis niloticus) in 2008 and plays an important role in gender differentiation in many reports. However, it is unclear whether it affects ovarian development. Turbot (Scophthalmus maximus) is an economically valuable flatfish species that is widely farmed in Europe and China. It cannot spawn eggs naturally in captivity and needs to be hand-stripped and artificially fertilized. The IGF system plays an important role during turbot ovary maturation. In this study, the full-length turbot IGF3 sequence was obtained via RACE cloning technology, its bioinformatics characteristics were analyzed, and the tertiary structure and docking situation were predicted. The relative expression levels during the whole tissue and ovarian development were detected using qRT-PCR. Hematoxylin-eosin staining was used to determine the gonadal development stage. The results showed that the full-length cDNA sequence of turbot IGF3 was 1 255 bp, encoding 259 amino acids, and displayed the highest homology with halibut (Hippoglossus stenolepis). A total of 33 amino acid signal peptides and 59 amino acid IGF-specific domains were found. It was a hydrophilic protein with a molecular mass of 26.39 kDa and a hydrophobic isoelectric point of 8.13. The turbot IGF3 is highly homologous with other fish. Turbot IGF3 is a hydrophobic protein, and its tertiary structure consists of three α spirals connected in series, closely integrated with IGF-1R and IGF-2R. igf3 is expressed differently between female and male turbot. In the liver, kidney, stomach, gonads, and brain, the male IGF3 expression was significantly higher than in females. In the heart, intestines, and pituitary gland, female IGF3 expression was significantly higher than males; however, the difference was not significant in the spleen. In male turbot, igf3 is mostly expressed in the brain, while in female turbot, igf3 is mostly expressed in the brain and intestine. During the five stages of development of turbot ovaries (previtellogenesis, early vitellogenesis, late vitellogenesis, migratory nucleus, and atresia), igf3 expression increased significantly in late vitellogenesis and maintained high expression in the migratory nucleus stage and decreased in the atresia stage. The results showed that turbot IGF3 has typical IGF family structure characteristics: local endocrine factors, widely distributed in tissues, significant sex dimorphism, and participates in regulating the growth and maturation of oocytes. Therefore, these findings lay a foundation for an in-depth research on the effects of IGF3 on ovarian development and oocyte maturation in turbot and provides crucial ideas for exploring the novel functions of IGF3 in fish.