Functional Dualism of Transposon Transcripts in Evolution of Eukaryotic Genomes

摘要

The ability of transposons to unite genes separated by their insertions encoding common biological processes into regulatory networks contributed, simultaneously with the complication of eukaryotes, to their evolutionary success by forming new universal systems. By means of these systems, including DNA methylation, histone modifications, the relationship of telomeres with transposons, splicing regulation, and RNA interference, global distribution of transposons in the genomes was accompanied by the emergence of their structural innovations, dynamic regulatory sequences, and protein-coding genes. The mobile elements contributed to the evolution of protein-coding genes by their duplication, as well as exonization, and domestication of the transposons themselves. The resulting new genes contain transposon sequences involved in their management by means of regulatory networks and noncoding RNAs also originating from the mobile elements. A strategy wherein the translation of noncoding RNA genes contributed to the selection of the obtained polypeptides as functional cellular proteins was developed during evolution. At the same time, noncoding RNAs are also processed into molecules involved in the regulatory processes independently or as a part of the protein complexes. The duality of functions was inherent to all noncoding RNAs whose nonrandom decay/processing leads to the formation of molecules that have a regulatory effect on the transposons and protein-coding genes. A strategy wherein primary transposon transcripts interact with different systems of their processing (arisen to protect the hosts from transposons), forming functional RNA molecules translated into the peptides, was developed in the evolution of eukaryotes. The transposons are universal sources for these strategies; this explains their global distribution in eukaryotic genomes and domestication in the system of "double search" for targets for functional interaction of noncoding RNAs and processed products of their translation. In addition to splicing, primary transcripts of some protein-coding genes can also be processed in functional noncoding RNAs involved in common biological reactions with the gene protein product. This substantiates the associations of multifactorial diseases with the gene SNP since they can cause inactivation of RNA domains. It was suggested that functional dualism of the transposon transcripts could be an important condition of the emergence of life, while the mobile elements are one of fundamental properties of living.