Comparative endocrinology on the pituitary gland of lampreys and hagfish

七鳃鳗和七鳃鳗是现存的仅有的两种脊椎动物的代表，无颌鱼。本研究旨在通过免疫组织化学和分子生物学技术对七鳃鳗和七鳃鳗的脑垂体系统进行研究。1)对海鳗(Petromyzon Marinus)脑垂体腺细胞类型进行了研究。结果发现，ACTH样细胞分布于远吻部的大部分部位，而MSH样细胞几乎分布于中间部的全部部位。在远侧部近侧，GH样细胞占据背侧，GTH样细胞位于腹侧。因此，至少有四种类型的腺垂体细胞存在于七鳃鳗脑垂体中。2)从七鳃鳗脑下垂体中克隆了编码GHS保守氨基酸序列的基因，并从其脑组织中分离出成熟蛋白。该蛋白在肝脏中的表达增强，证明该蛋白为七鳃鳗生长激素。3)对不同生活史阶段的七鳃鳗的腺垂体细胞类型的个体发育进行了研究。结合七鳃鳗的生活史讨论了所获得的结果。4)研究了大西洋和太平洋鳗鱼、粘液鳗、沙棘和副粘液鳗脑垂体腺垂体细胞的免疫反应类型。在这三个物种中，在腺垂体中都检测到了三种不同类型的激素细胞。它们是ACTH样细胞、GH样细胞和GTH样细胞。推测ACTH、GH和GTH是古老的激素，在脊椎动物进化过程中保持其原有的功能，而后来衍生的激素如PRL和TSH可能促进了脊椎动物向新环境的扩展。

Lampreys and hagfish are the only two extant representatives of the oldest class of vertebrates, Agnatha (jawless fishes). The present study aimed to elucidate the pituitary system of lampreys and hagfish by means of both immunohistochemical and molecular biological techniques. 1) Adenohypophysial cell types were studied in the sea lamprey (Petromyzon marinus) pituitary gland. It was found that ACTH-like cells were distributed in most parts of the rostral pars distalis, whereas MSH-like cells in almost all parts of the pars intermedia. In the proximal pars distalis, GH-like cells occupied the dorsal half, while GTH-like cells in the ventral half. Thus, at least four types of adenohypophysial cells are present in the sea lamprey pituitary. 2) A cDNA coding conserved amino acid sequence in gnathostome GHs has been cloned from the sea lamprey pituitary, followed by the isolation of the mature protein from the sea lamprey pituitary. That protein has been identified to be lamprey GH by demonstrating an increase of expression of lamprey IGF gene in the liver. 3) Ontogeny of adenohypophysial cell types was studied in sea lampreys at several different stages of the life cycle. Results obtained were discussed in connection with the life cycle of sea lampreys. 4) Immunoreactive adenohypophysial cell types were studied in the pituitary of the Atlantic and the Pacific hagfish, Myxine glutinosa, Eptatretus burgeri and Paramyxine atami. In all three species, three different types of hormone cells were detected in the adenohypophysis. They were ACTH-like cells, GH-like cells and GTH-like cells. It is suggested that ACTH, GH and GTH are ancient hormones and maintain their original functions throughout vertebrate evolution, while the later derived hormones, such as PRL and TSH, may have contributed to the expansion of vertebrates into new environments.