SILVER, M.R.*; SOWER, S.A.; Univ. of New Hampshire: The Lamprey Lineage: A Phylogenetic Perspective

Lamprey are members of the oldest class of living vertebrates, the agnathans, which diverged from the main line of vertebrate evolution approximately 500 million years ago. Their divergence is believed to have occurred between two proposed early genome duplications, making the lamprey an important model for evolutionary biology. Despite this interest in the lamprey, very little is known about their phylogeny. The lamprey lineage is generally considered to be divided into three families, the Petromyzonidae, or holarctic family, found in the northern hemisphere, and the two southern hemisphere families, the Geotriidae and Mordaciidae. The phylogeny of these families has been primarily based on size, shape, and distribution of dentition. The objective of this research was to isolate and sequence the cDNA precursor of lamprey GnRH-III in representative species of each of the three families of lamprey in order to assess their phylogenetic relationship. The cDNA encoding prepro-lamprey GnRH-III was isolated using a PCR based subcloning procedure from 6 holarctic species, Petromyzon marinus, Lampetra tridentatus, L. appendix, L. richardsoni, Ichtiomyzon unicuspis, I. fossor, and one from each southern hemisphere species, Geotria australis and Mordacia mordax. Using PAUP v40.b8, the molecular phylogenetic relationship of lamprey GnRH-III between the three families of lamprey was investigated. These data suggest that the lamprey GnRH-III cDNAs of the two southern hemisphere species are highly divergent from the lamprey GnRH-III cDNA of the holarctic species. (Supported by the NSF to SAS)