Identification of adenohypophysial hormones from the hagfish pituitary gland and its evolutional implication

本研究旨在利用免疫组织化学和分子生物学技术研究盲鳗的垂体系统。腺垂体细胞类型进行了研究，在垂体的大西洋和太平洋盲鳗，使用抗血清四足动物和鱼类垂体激素。在腺垂体中检测到三种不同类型的免疫反应细胞，它们似乎与促性腺激素（GTH）样细胞、生长激素（GH）样细胞和促肾上腺皮质激素（ACTH）样细胞相对应。在随后的研究中，GTH样物质的量和性腺条件之间的关系进行了检查，在棕色八目鱼（副粘热海），太平洋八目鱼之一。免疫反应性GTH样物质大量积累在成年人与发展中的性腺，而它不是或只有弱积累在青少年或成年人没有发展中的性腺。热海幼鱼腹腔注射苯甲酸雌二醇后，腺垂体中GTH样物质的强度与对照组相比显著增加。GTH的α-和β-亚基的cDNA已经从P.热海的脑垂体中克隆出来（Nozaki等，未出版）。GTHα的氨基酸序列与颚口类糖蛋白α亚基的同源性为39-44%，GTHβ与颚口类LHβ、FSHβ和TSHβ的同源性为30-43%。这些结果表明GTH存在于盲鳗脑垂体中。

The present study aimed to elucidate the pituitary system of hagfish by means of immunohistochemical and molecular biological techniques. Adenohypophysial cell types were studied in the pituitaries of the Atlantic and the Pacific hagfish, using antisera to tetrapod and fish pituitary hormones. Three different types of immunoreactive cells were detected in the adenohypophysis, which appeared to correspond with gonadotropin (GTH)-like, growth hormone (GH)-like and adrenocorticotropin (ACTH)-like cells. In the subsequent study, the relationship between the amount of GTH-like material and gonadal conditions was examined in the brown hagfish (Paramyxine atami), one of the Pacific hagfish. Immunoreactive GTH-like material was heavily accumulated in adults with developing gonads, whereas it was not or only weakly accumulated in juveniles or adults without developing gonads. Following intraperitoneal administration of estradiol benzoate in juvenile animals of P.atami, the intensities of GTH-like material in the adenohypophysis increased significantly when compared to those of controls. cDNAs of both α- and β-subunits of GTH have been cloned from the pituitary gland of P.atami (Nozaki et al., unpublished). The deduced amino acid sequence of the hagfish GTHα shows 39-44% identity to α-subunits of gnathostome glycoproteins, and the hagfish GTHβ shows similar identity (30-43%) with gnathostome LHβ,FSHβ, and TSHβ. These results indicated the presence of GTH in the hagfish pituitary gland.