In modern developmental biology, great importance is attached to the study of molecular mechanisms of morphogenesis control. It is now believed that a huge variety of animal forms has been achieved during evolution due to changes in genetic development programs. The elements of these programs are studied by analyzing the process of their interaction with each other, which form a complex regulatory network that determines the individual plan of the body structure, the determination, and the differentiation of individual tissues and organs.
The first stage in development is the regionalization of the embryo, that is, the division of one morphogenetic zygote field into individual cell domains and their further specification. This process is controlled by various regulatory genes organized into an expanding hierarchical cascade. At the next stage, the fate of cells in the already formed domains is determined. The transcription factors activated here include the genes of the last stage of specialization – the genes of tissue differentiation. HOX-genes are key regulators of various morphogenetic programs. The discovery of the class of HOX genes occurred as a result of the study of homeosis mutations.
Mutations of this kind lead to the ectopic appearance of various structures. An example is the development of a leg instead of an antenna in an insect, the appearance of ribs on the cervical vertebrae invertebrates. The main works on the study of HOX genes were performed on a fruit fly and mouse, and are currently being studied in a wide range of animals. HOX-genes encode proteins are transcription factors containing a DNA-binding domain consisting of 60 amino acid residues. HOX proteins work in the form of heterodimers with other transcription factors and cofactors, and dimerization determines the specificity of recognition.
Functional analysis of HOX genes of various bilateral animals revealed the main function of these genes. They take part in the regulation of the formation of the regional specificity of the body along the anteroposterior axis. The HOX-gene cluster functions within a complex regulatory network that defines the body structure plan. The mechanisms that ensure the morphological diversity of forms within taxonomic groups lie mainly in changes in the regulatory relationship in the conservative set of genes in the existing regulatory network.