Regulation of gene expression in developmental process
Gene expression is a complex, regulated process that begins with DNA duplication, DNA transcription in which DNA transcribed into RNA, which is then translated into protein. Each somatic cell in the body generally contains the same DNA. A few exceptions include red blood cells, which contain no DNA in their mature state, and some immune system cells that rearrange their DNA while producing antibodies. Genes are molecularly regulated constrain our understanding of how they might exert their control over development in health and disease.
The hox gene were discovered in Drosophila (Bridges and Morgan, 1923), where they exist in two separate gene clusters. Early genetic experiments in adult flies demonstrated that Hox genes are involved in the allocation of distinct morphological identities to each body segment: mutations affecting specific Hox genes typically lead to homeotic transformations, in which the morphology of a given segment is transformed into the likeness of another (Bateson, 1894). This innovative research suggested that Hox genes provide a genetic coordinate system for the allocation of developmental identities in the fly. However, understanding the mechanisms that link Hox genes to their developmental roles was only possible when the relevant genes were cloned, and their expression domains in the fly embryo, as well as their regulation, clarified. Indeed, molecular cloning of the BX-C (Bender et al., 1983) followed by expression analysis showed that Hox genes are expressed in particular subdomains along the anteroposterior axis of the embryo (Akam, 1987; Harding et al., 1985).