HAVIRD, J/C*; CHOE, K/P; EVANS, D/H; University of Florida, Gainesville; University of Florida, Gainesville; University of Florida, Gainesville: The evolution of cyclooxygenase in ancestral chordates

In mammals, prostaglandins (PGs) are involved in many physiological processes such as blood clotting, inflammation and regulation of vascular tone and osmoregulation. Cyclooxygenase (COX) is one of the major enzymes involved in PG synthesis. In mammals there are two COX subtypes, COX-1 and COX-2, but COX orthologues have been found in many chordates including the sea squirt (Ciona intestinalis). In the mammalian kidney, COX-2 generated PGs inhibit ion transport and support cell survival during salt loading and dehydration. Our lab has previously confirmed a COX-2 orthologue in the gills of the euryhaline killifish (Fundulus heteroclitus), and evidence suggest that COX-2 (and COX-1) generated PGs may influence ion and water balance in fishes. However, it is unknown whether ancestral chordates possess COX-1 and COX-2 or a precursor (COX-A and COX-B) as in found in the sea squirt. The goals of this project were to determine the COX cDNA sequence(s) from the following ancestral chordates: lancelet (Branchiostoma lanceolatum), hagfish (Myxine glutinosa), lamprey (Petromyzon marinus), and also the COX-1 sequence from the killifish, and to determine the phylogenetic relationship between the chordate COXs. Using standard RT-PCR and cloning procedures, we have obtained the first partial COX cDNA sequences from the lancelet, hagfish gill, and lamprey gill, as well as a COX-1 orthologue from the killifish gill. Phylogenetic analysis suggests that lancelets and hagfish have a COX precursor (COX-A and COX-B), whereas lampreys have COX-1 and COX-2, as found in elasmobranchs, teleosts and mammals. Our data predicted the evolution of COX-1 and COX-2 at around 600 million years ago.