The molecular mechanism of restricting telomeric transposons.

Linear chromosomes of eukaryotes are protected by a DNA-protein-RNA structure called telomere. Remarkably and unlike those of most organisms studied, telomeric DNA is not composed of a group of short repeats, but three classes of retrotransposons at the chromosome ends. Telomeric transposons in on the other hand serves the function of elongating the host chromosomes yet prevent little harm to the host genome as their insertion sites are strictly limited to the telomere. How the host achieves such precise regulation is still unclear. The currently known genome-wide repression of transposon expression includes piRNA pathway and the heterochromatin pathway involving H3K9me3. Recent studies have found that telomere capping proteins are involved in the specific regulation of telomeric retrotransposons. In this review, we discuss the specific functions of telomere capping proteins in regulating telomeric transposons. By studying how the host interacts and regulates telomeric transposons, we hope to shed lights on universal principles in guiding their co-evolution.