Distribution of proopiocortin (POC) and proopiomelanotropin (POM) mRNA during development of the sea lamprey: A quantitative spatial and temporal in situ hybridization study

The sea lamprey, Petromyzon marinus, undergoes a complex life cycle beginning with a filter feeding larval stage followed by a seven stage non-trophic metamorphosis, an actively feeding parasitic adult stage and spawning adult stages. The lamprey has ancient origins and conservative evolution but the full extent and the role of hormones the lamprey pituitary secretes is unknown. Recently, two POMC-like pituitary prohormones proopiocortin (POC) and proopiomelanotropin (POM) have been characterized from adult sea lamprey. POC and POM are multi-domain prohormones. POC encodes a nasohypophysial factor (NHF), ACTH, a MSH, and $\beta$-END and POM encodes MSH-A, MSH-B and $\beta$-END. In this study, radiolabelled riboprobes were generated specifically to the NHF domain of POC mRNA and MSH-B domain of POM mRNA in order to examine the expression of POC and POM during development of the sea lamprey by in situ hybridization. Results would implicate the role of POM and POC perhaps not in the initiation of metamorphosis but in some processes necessary for development of the lamprey. The very high levels of POM and POC expression in spawning animals suggest a role in the sexual maturation of lampreys. (Abstract shortened by UMI.).