Illuminating the dark side of the genome

Almost 50 percent of our genome is made up of highly repetitive DNA, which makes it very difficult to be analysed. 

In fact, repeats are discarded in most genome-wide studies and thus, insights into this part of the genome remained limited.

Scientists from the Max Planck Institute of Immunobiology and Epigenetics (MPI-IE) in Freiburg now succeeded in examining this dark side of the genome. Their analyses revealed that repeat-associated heterochromatin is essential to repress retrotransposons and thereby protects the genomic integrity of stem cells.

This work opens the way for future genome-wide analyses of repetitive regions in the genome and is in line with newly emerging functions for heterochromatin.

Only 1 % of the human genome contains coding information, while the remaining 99 % harbour non-coding and repetitive DNA. DNA and its packaging proteins (histones) create a polymer called chromatin that also regulates gene expression. There are two major chromatin states: Euchromatin is open or accessible and thus, genes can be activated. In contrast, heterochromatin is closed or inaccessible and therfore, genes are repressed.

A research team led by Prof. Dr. Thomas Jenuwein, director at the MPI-IE, now investigated these genome areas in mouse stem cells using heterochromatin factors. They conducted genome-wide mapping for the enzyme 'histone methyltransferase Suv39h', one of the most prominent enzymes involved in heterochromatin formation.