ROLE OF TRANSPOSABLE ELEMENTS IN EMERGENCE OF Metazoa
Animals from the subkingdom Metazoa are distinguished by the features of universal systems of regulation of gene expression necessary for species-specific cell differentiation in the body. These systems originally arose for the protection of the genome from insertions of mobile genetic elements and are represented by the mechanisms of splicing regulation, RNA interference, epigenetic factors, and lncRNA. The inherited species-specific transpositions of mobile genetic elements in embryogenesis and the preservation of their activity in certain tissues of adult organisms have been confirmed. It is suggested that in the evolutionary occurrence of Metazoa, the mechanisms of self-regulation of transposons in interrelation with gene networks controlling their activity allowed coordination of cells among themselves, with each subsequent division with differentiated expression of genes and the formation of tissues and organs. In the process of natural selection, species-specific features of the amount, composition, and location of transposons in the genomes of eukaryotes could form the basis for the creation of specific dynamic complexes for the regulation of gene networks. These complexes were formed because noncoding RNA of transposon origin affects DNA methylation, histone modifications, and processing of alternative splicing variants. The enormous prevalence of mobile genetic elements in the genomes of eukaryotes allows the activation of certain transposons for the modification of expression-specific genes, which plays a key role in the differentiation of cells in ontogenesis. It is suggested that animals with optimal composition and arrangement of transposons that can form a cascade of their activation are able to survive in evolution, which, due to self-regulation, starting from the division of the zygote, forms a species-specific pattern of controlling the expression of genes that underlies differentiation. Each species of multicellular eukaryotes is characterized by the presence of a specific karyotype, which is formed mainly by the functioning of transposons. Each genome contains information embedded in the location of repeats with respect to each other and protein-coding genes, which forms a complex system of biological coding underlying the species-specific features of ontogenesis.