Evolution of the vertebrate ParaHox clusters.

The ParaHox cluster contains three Hox-related homeobox genes. The evolution of this sister of the Hox-gene clusters has been studied extensively in metazoans with a focus on its early evolution. Its fate within the vertebrate lineage, and in particular following the teleost-specific genome duplication, however, has not received much attention. Three of the four human ParaHox loci are linked with PDGFR family tyrosine kinases. We demonstrate that these loci arose as duplications in an ancestral vertebrate and trace the subsequent history of gene losses. Surprisingly, teleost fishes have not expanded their ParaHox repertoire following the teleost-specific genome duplication, while duplicates of the associated tyrosine kinases have survived, supporting the hypothesis of a large-scale duplication followed by extensive gene loss.