Origin and evolution of pituitary hormones : identification of hormone genes in an agnathans

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This study aimed to understand the origin and evolution of endocrine systems of reproduction, growth and adaptation in vertebrates based on the identification of brain and pituitary hormones and receptor in an agnathans, lampreys.1.Pituitary hormones(1)We identified a gonadotropin (GTH) β subunit from the sea lamprey pituitary, showing intermediate sequence similarity to both follicle-stimulating hormone (FSH) β and luteinizing hormone (LH) β subunits. The GTH-producing cells were located in the ventral half of the proximal pars distalis of the pituitary. GTHβ subunit mRNA was stimulated by lamprey gonadotropin-stimulating hormones (GnRH). The results indicate that lamprey has a single GTH gene. We hypothesized that a single GTH gene occurred in a strain of agnathan, hence FSH and LH may have appeared in gnathostomes.(2)We determined the structures of GTHβ subunit, growth hormone (GH), proopiocortin (POC) and proopiomelanotropin (POM) genes in sea lamprey.(3)We demonstrated the presenc … More e of POC and POM genes in the pouched and short-headed lampreys, as in the sea lamprey. These findings suggest that the duplication event which generated the two genes may have occurred in a common ancestor of the three extant lampreys.2.Glycoprotein hormone receptor.We identified two kinds of glycoprotein hormone receptor cDNAs from sea lamprey : one is a GTH-like receptor located in the gonad and the other is a TSH-like receptor located in the thyroid tissue. These strongly suggest that GTH and TSH also exist in agnathans3.Brain hormones(1)We identified two homologues of prolactin-releasing peptide (RFa-A and B) from the sea lamprey brain. RFa immunoreactive cells were detected not only in the hypothalamus but also in the pars intermedia of the pituitary. Both RFa-A and B inhibited the expression of GH and POM mRNAs in the pituitary.(2)We cloned GnRH-III cDNAs from eight species of lamprey representing the three families of Petromyzoniformes. The sequences of GnRH-III can be divided into three groups supporting the current view of the lamprey lineage at the family level. Less