Homeodomain Proteins

Abstract

Homeodomain proteins are DNA-binding proteins that play major roles in many developmental processes of animals as well as fungi and plants. The homeodomain is a protein domain of about 60 amino acids that binds DNA. Proteins containing a homeodomain can regulate the expression of other genes in development and differentiation. Hundreds of homeobox genes have been identified, and they can be grouped into many different classes. Often, other conserved protein domains are found linked to a homeodomain. Several particular types of homeobox genes lie next to each other on the chromosome in clusters. The best-known cluster, the HOX cluster, is found in all bilateral animals. Vertebrates contain four HOX clusters that have arisen through duplication in early vertebrate evolution; its genes are called Hox genes. Lower chordates, insects, and nematodes have only one HOX cluster. Of particular interest is that many of the HOX cluster genes function in the process of pattern formation along the anterior–posterior body axis. However, a lot of homeobox genes are not found in clusters and do not function in pattern formation, but play roles in the determination of cell fates and cell differentiation. Homeobox genes thus perform key roles for all aspects of the development of an organism.