Highly Divergent Homeobox Protein (HDX)

The homeobox genes are a large and diverse group of genes, many of which play important roles in the embryonic development of animals. Increasingly, homeobox genes are being compared between genomes in an attempt to understand the evolution of animal development.

HDX encodes a highly divergent atypical homeodomain but not a POU-specific domain, and thus it is debatable whether it should be placed within the POU class. Phylogenetic analyses of homeodomains place it basally in a clade with the POU class , or within the POU class, suggesting that the HDX protein either diverged before the POU-specific domain became associated with the homeodomain or lost the POU-specific domain during evolution.