Molecular studies of pituitary hormones during the life cycle of the lamprey

This investigation focused on identifying and sequencing pituitary prohormones from the sea lamprey (Petromyzon marinus). The evolutionary lineage of lampreys can be traced back approximately 350 million years. The expression of these prohormones gives insight into the regulation of key events during the lamprey life cycle such as metamorphosis and sexual maturation. During this study, the first pituitary prohormone in lampreys, proopiomelanocortin (POMC) was cloned from sea lampreys and it was shown that there is a divergence in the DNA sequence of this precursor compared to vertebrate POMC. In the sea lamprey, adrenocorticotropin or corticotropin (ACTH) and melanocyte-stimulating hormone or melanotropin (MSH) are encoded on distinct genes, eventually these genes were termed proopiocortin (POC) and proopiomelanotropin (POM), respectively. POC encodes nasohypophysial factor (NHF), ACTH, a MSH, and β-endorphin while POM encodes MSH-A and -B peptides and a second form of β-endorphin. Complete cDNAs of POC and POM were also cloned from the American brook lamprey, Lampetra appendix.; Examination of the variation in expression of these two genes, POC and POM, during the life cycle of a parasitic lamprey (P. marinus) and a nonparasitic lamprey (L. appendix) showed an earlier increase in expression of POC and POM in the nonparasitic species during metamorphosis. These results suggest that the prohormones likely play a substantial role in development and maturation events which ultimately are related to the adult life history.; Preliminary work using differential display was conducted to analyze altered gene expression at the mRNA level in the pituitary between larvae and stage 4 metamorphosing lampreys. Two of the twenty genes selected that showed higher expression in the larvae showed strong similarity to lamprey cytochrome-c oxidase and some similarity to vertebrate pituitary prohormone gonadotropin-II β.; During this investigation it was difficult to identify the classical types of pituitary prohormones in lampreys using conventional molecular approaches. This difficulty may be due to the fact that the lamprey is ancient in lineage and the hormones do not contain conserved sequences found in other vertebrates. The result from differential display encourages further work to identify differentially expressed hormones that regulate the development of the lamprey.