Hox Genes

Abstract

Hox genes were first identified through mutations causing the dramatic transformation of one body structure into another in fruit flies, and later isolated across the animal kingdom. Hox genes arose from a single gene by tandem duplications during evolution and linked in chromosomal clusters. A striking feature of Hox genes is the direct correlation between their physical arrangement within the clusters and the spatiotemporal expression pattern during embryogenesis. This property, termed colinearity, results in the establishment of nested domains of gene expression along the anterior–posterior body axis and generates a combinatorial Hox code used for specifying positional identities during development. Comparative studies of Hox gene regulation in many species have revealed that the precise control of expression is achieved through a variety of regulatory mechanisms and have broadened our understanding of the regulatory network governing body patterning. Hox genes encode homeodomain transcription factors that regulate downstream genes by directly binding to DNA sequences. Misregulation of Hox genes leads to developmental defects including homeotic transformations and implicated in leukemia and other pathological conditions in humans. Alternations in Hox protein function or expression have also been linked to the evolution of animal body plans.