Evolutionary Plasticity of Vertebrate Hox Genes

Comparative studies of the molecular control of development in diverse animal groups have revealed a surprising conservation in the genetic control of animal development. A dramatic demonstration of this conservation is seen in the expression and function of Hox genes deployed along the animal anterior-posterior (A-P) body axis, where similar expression and function of Hox genes are seen in animals as diverse as nematodes, insects and vertebrates. With the genome sequences of several metazoans now in hand and the availability of BAC genomic libraries from additional species, researchers have begun to characterize the genomic changes underlying divergent developmental programs. This review summarizes the role of Hox genes in evolution of the vertebrates. General patterns of Hox cluster evolution among the major lineages of vertebrates are described including lineage-specific instances of cluster duplication and gene loss. Following this are brief descriptions of the evolving role of Hox genes in evolution of primitive vertebrates, and their subsequent roles in evolution of vertebrate axial and appendicular diversity. A conceptual theme uniting all these studies is the remarkable plasticity of Hox genes in the evolution of vertebrate diversity. Finally, the increasingly important roles of experimental advances in genomics and bioinformatics are discussed along with suggestions for future directions in vertebrate Hox research.