Epigenetic regulation of genes mediated by satellite DNA

Epigenetic regulation of genes mediated by satellite DNA Isidoro Feliciello, Ivana Akrap, Đurđica Ugarković Satellite DNA is a highly repetitive DNA, organized in long tandem arrays, located in the heterochromatic regions of chromosomes. Due to intrastrand homologous recombination, elements of satellite DNAs can be excised from their heterochromatin loci and integrate into euchromatin. This scenario was proposed to describe euchromatic dispersion of TCAST, the species-specific major satellite DNA of beetle Tribolium castaneum, which is found associated with numerous protein-coding genes. Dispersed repeats of TCAST (dTcast) were present as monomeric or multimeric repeat units in intragenic (introns), as well as, intergenic regions. Our assumption was that dTcast can influence the expression of associated genes. Our results show that dTcast does not significantly affect the level of gene expression under physiological condition but induces a transient downregulation of gene transcription after heat stress. Interestingly, also the level of TCAST satellite transcripts in the form of siRNAs and TCAST satellite DNA methylation as well as H3K9 met2/3 in heterochromatin are temperature modulated. We showed a temporary formation of heterochromatic state characterized by increased level of H3K9met2/3 at dTcast insertion sites and their spreading to the proximal regions. Such “heterochromatinization” occurs after heat stress and correlates with transcriptional downregulation of nearby genes. In conclusion, dTcast satellite elements influence the level of expression of their associated genes through RNA interference-based “heterochromatinization” which occurs transiently after heat stress. What is the physiological consequence of this satellite DNA-mediated modulation of gene expression remains to be elucidated.