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 threeloci in all vertebrates examined, with the exception of lampreys, whichhave a single LDH locus. Biochemical characterizations of LDH proteins havesuggested that a gene duplication early in vertebrate evolution gave riseto Ldh-A and Ldh-B and that an additional locus, Ldh-C arose in a number oflineages more recently. Although some phylogenetic studies of LDH proteinsequences have supported this pattern of gene duplication, others havecontradicted it. In particular, a number of studies have suggested thatLdh-C represents the earliest divergence among vertebrate LDHs and that itmay have diverged from the other loci well before the origin ofvertebrates. Such hypotheses make explicit statements about therelationship of vertebrate and invertebrate LDHs, but to date, no closelyrelated invertebrate LDH sequences have been available for comparison. Wehave attempted to provide further data on the timing of gene duplicationsleading to multiple vertebrate LDHs by determining the cDNA sequence of theLDH of the tunicate Styela plicata. Phylogenetic analyses of this and otherLDH sequences provide strong support for the duplications giving rise tomultiple vertebrate LDHs having occurred after vertebrates diverged fromtunicates. The timing of these LDH duplications is consistent with datafrom a number of other gene families suggesting widespread gene duplicationnear the origin of vertebrates. With respect to the relationships amongvertebrate LDHs, our data are not consistent with previous claims thatLdh-C represented the earliest divergence. However, the preciserelationships among some of the main lineages of vertebrate LDHs were notresolved in our analyses.