Genome Duplications and Accelerated Evolution ofHoxGenes and Cluster Architecture in Teleost Fishes

The early origin of four vertebrate Hox gene clusters during the evolution of gnathostomes was likely caused by two consecutive duplications of the entire genome and the subsequent loss of individual genes. The presumed conserved and important roles of these genes in tetrapods during development led to the general assumption that Hox cluster architecture had remained unchanged since the last common ancestor of all jawed vertebrates. But recent data from teleost fishes reveals that this is not the case. Here, we present an analysis of the evolution of vertebrate Hox genes and clusters, with emphasis on the differences between the Hox A clusters of fish (actinopterygian) and tetrapod (sarcopterygian) lineages. In contrast to the general conservation of genomic architecture and gene sequence observed in sarcopterygians, the evolutionary history of actinopterygian Hox clusters likely includes an additional (third) genome duplication that initially increased the number of clusters from four to eight. ...