UCLA

Transposons and genes are silenced in eukaryotes through DNA methylation. In this work, mutations in the Arabidopsis genes CRT1 and CRH6, two ATPases in the conserved Microrchidia (MORC) family, are found to release silencing of DNA methylated transposons and genes without an accompanying loss of DNA methylation. The loci upregulated in crt1 and crh6 mutants are located primarily in the regions of pericentromeric heterochromatin. CRT1 and CRH6 are located in small nuclear bodies adjacent to the regions of condensed pericentromeric heterochromatin called chromocenters. In the absence of MORC function, chromocenters decondense and interactions between pericentromeric and euchromatic regions increase. The single Caenorhabditis elegans MORC homolog is also shown to be required for gene silencing. These studies demonstrate that MORC ATPases are required for proper heterochromatin condensation and have a conserved role in gene silencing in eukaryotes.