Evolution of CpG-islands by means of tandem duplications

Abstract

CG-rich islands (CpG-islands, or CGI) are important functional elements in a genome of vertebrates. In particular, they: a) initiate transcription as promoters in most (> 50 %) genes of vertebrates, in some cases bi-directional, due to self-complement feature of cg dinucleotides; b) form a global methylation landscape; c) act as a transcription “switch” via methylation. The degenerate nature of CpG-island (elevated CG composition) implies an increase in the probability of tandem repeats and palindromes within CpG- island. This work is devoted to the identification of tandem duplications of complete CpG-islands, i. e. considering mega monomers of size 400–5 000 bp, in the human genome. We found a range of inter- and intragenic tandem duplications of CpG-islands. Intergenic CpGi duplication mediates through CG-rich telomeric satellites, as well as elements of the SINE. One of the most pronounced tandems are located in chromosome 19, known for its abundance of segment duplications and gene expansion. We also underline the unique genomic segment, which is DXZ4 mega satellite, in q arm of chromosome X, also falling into the category of CpG-islands which evolved by tandem duplications rounds.

Keywords

• cpg-islands
• tandem repeats
• macrosatellites
• human genome
• methylation
• cpg-island clusters.