LACTATE-DEHYDROGENASE (LDH) GENE DUPLICATION DURING CHORDATE EVOLUTION - THE CDNA SEQUENCE OF THE LDH OF THE TUNICATE STYELA-PLICATA

L-Lactate dehydrogenase (L-LDH, E.C. 1.1.1.27) is encoded by two or th ree loci in all vertebrates examined, with the exception of lampreys, which have a single LDH locus. Biochemical characterizations of LDH pr oteins have suggested that a gene duplication early in vertebrate evol ution gave rise to Ldh-A and Ldh-B and that an additional locus, Ldh-C arose in a number of lineages more recently. Although some phylogenet ic studies of LDH protein sequences have supported this pattern of gen e duplication, others have contradicted it. In particular, a number of studies have suggested that Ldh-C represents the earliest divergence among vertebrate LDHs and that it may have diverged from the other loc i well before the origin of vertebrates. Such hypotheses make explicit statements about the relationship of vertebrate and invertebrate LDHs , but to date, no closely related invertebrate LDH sequences have been available for comparison. We have attempted to provide further data o n the timing of gene duplications leading to multiple vertebrate LDHs by determining the cDNA sequence of the LDH of the tunicate Styela pli cata. Phylogenetic analyses of this and other LDH sequences provide st rong support for the duplications giving rise to multiple vertebrate L DHs having occurred after vertebrates diverged from tunicates. The tim ing of these LDH duplications is consistent with data from a number of other gene families suggesting widespread gene duplication near the o rigin of vertebrates. With respect to the relationships among vertebra te LDHs, our data are not consistent with previous claims that Ldh-C r epresented the earliest divergence. However, the precise relationships among some of the main lineages of vertebrate LDHs were not resolved in our analyses.