In Science this week, a group led by researchers from the University of Zurich publish high-resolution crystal structures of two major subtypes of Cas9 enzymes, the nucleases responsible for the double-strand DNA breaks that occur with CRISPR-based gene editing. The work provides new insights into how Cas9 interacts with guide RNA to determine target DNA binding, and may give other researchers clues on how to better engineer CRISPR systems for gene editing.
Also in Science, a multi-institute team of scientists report on their efforts to better understand the effect of heritable epigenetic variation on complex traits. They analyzed a population of isogenic Arabidopsis lines that have almost identical DNA sequences, but segregate many differences in DNA methylation, and found that many of these so-called differentially methylated regions (DMRs) act as epigenetic quantitative trait loci. Notably, these accounted for between 60 percent and 90 percent of the heritability for two complex traits: flowering time and primary root length. Many of the DMRs examined are variable in natural populations of the plant, suggesting that they may be an epigenetic basis for evolution independent of DNA sequence changes.