Zebrafish <i>hox</i> Clusters and Vertebrate Genome Evolution

TLDR

HOX genes determine anterior‑posterior cell fate, and the increase from one cluster in invertebrate chordates to four in mammals implies that cluster duplication helped evolve vertebrate body plans. Phylogenetic and mapping data indicate a whole‑genome duplication event after ray‑finned and lobe‑finned fish divergence but before teleost diversification. Zebrafish possess seven hox clusters, indicating that teleosts have more copies of these developmental genes than mammals, even though their anterior‑posterior axis is less complex.

Abstract

HOX genes specify cell fate in the anterior-posterior axis of animal embryos. Invertebrate chordates have one HOX cluster, but mammals have four, suggesting that cluster duplication facilitated the evolution of vertebrate body plans. This report shows that zebrafish have seven hox clusters. Phylogenetic analysis and genetic mapping suggest a chromosome doubling event, probably by whole genome duplication, after the divergence of ray-finned and lobe-finned fishes but before the teleost radiation. Thus, teleosts, the most species-rich group of vertebrates, appear to have more copies of these developmental regulatory genes than do mammals, despite less complexity in the anterior-posterior axis.