Stay CLASSY: Control of locus-specific de novo DNA methylation by the CLASSY family ($) (Nature Genet.)

DNA methylation is fundamental for genome function and stability, including regulation of gene expression, silencing of transposable elements and control of recombination. While the processes involved in maintenance of DNA methylation are generally well understood, the factors required for locus-specific de novo establishment of DNA methylation remain unclear.  In this study, Zhou et al. tested the role of chromatin remodelling factors from the CLASSY (CLSY) family in the de novo DNA methylation pathway in Arabidopsis. They showed that CLSYs interact with RNA polymerase IV and together mediate transcriptional silencing by controlling the production of 24-nt small-interfering RNA, which drive locus-specific de novo methylation. They further show that recruitment of CLSYs is driven by local enrichment in repressive chromatin modifications, such as DNA methylation in CG context and H3K9me2. Together, this study provides significant advances in understanding the initiation of de novo DNA methylation and highlights the interdependence between chromatin-based processes. (Summary by Matthias Benoit) Nature Genet. 10.1038/s41588-018-0115-y