Originally published as Genetics Published Articles Ahead of Print on October 16, 2004.

Genetics, Vol. 169, 807-817, February 2005, Copyright © 2005
doi:10.1534/genetics.104.031831

The Dlx Gene Complement of the Leopard Shark, Triakis semifasciata, Resembles That of Mammals

Implications for Genomic and Morphological Evolution of Jawed Vertebrates

David W. Stock1

Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, Colorado 80309-0334

1 Address for correspondence: Department of Ecology and Evolutionary Biology, N122 Ramaley, Campus Box 334, University of Colorado, Boulder, CO 80309-0334.
E-mail: david.stock{at}colorado.edu

Extensive gene duplication is thought to have occurred in the vertebrate lineage after it diverged from cephalochordates and before the divergence of lobe- and ray-finned fishes, but the exact timing remains obscure. This timing was investigated by analysis of the Dlx gene family of a representative cartilaginous fish, the leopard shark, Triakis semifasciata. Dlx genes encode homeodomain transcription factors and are arranged in mammals as three convergently transcribed bigene clusters. Six Dlx genes were cloned from Triakis and shown to be orthologous to single mammalian Dlx genes. At least four of these are arranged in bigene clusters. Phylogenetic analyses of Dlx genes were used to propose an evolutionary scenario in which two genome duplications led to four Dlx bigene clusters in a common ancestor of jawed vertebrates, one of which was lost prior to the diversification of the group. Dlx genes are known to be involved in jaw development, and changes in Dlx gene number are mapped to the same branch of the vertebrate tree as the origin of jaws.