Shining Light on the Dark Side of the Genome.

Heterochromatin has historically been considered the dark side of the genome. In part, this reputation derives from its concentration near centromeres and telomeres, regions of the genome repressive to nuclear functions such as DNA replication and transcription. The repetitive nature of heterochromatic DNA has only added to its "darkness", as sequencing of these DNA regions has been only recently achieved. Despite such obstacles, research on heterochromatin blossomed over the past decades. Success in this area benefitted from efforts of Sergio Pimpinelli and colleagues who made landmark discoveries and promoted the growth of an international community of researchers. They discovered complexities of heterochromatin, demonstrating that a key component, Heterochromatin Protein 1a (HP1a), uses multiple mechanisms to associate with chromosomes and has positive and negative effects on gene expression, depending on the chromosome context. In addition, they updated the work of Carl Waddington using molecular tools that revealed how environmental stress promotes genome change due to transposable element movement. Collectively, their research and that of many others in the field have shined a bright light on the dark side of the genome and helped reveal many mysteries of heterochromatin.