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This Week in PNAS: Jul 26, 2016

Washington State University researchers put together a map of ultraviolet light-induced damage across a yeast eukaryotic genome. Using an approach called cyclobutane pyrimidine dimer sequencing, or CPD-sequencing, the team tracked the formation of such dimers following UV exposure at the single nucleotide level over the genome, in relation to the broader nucleosome patterns and chromosomal landscape. Based on patterns in the yeast genome, the study's authors conclude that "UV damage is not uniformly distributed, but that damage formation is significantly modulated in a predictable way by nucleosomes and DNA-bound transcription factors."

For another PNAS study, a team from the UK and Germany explores connection changes accompanying adolescence in the human brain. Using brain imaging, the researchers attempted to tease apart changes in brain connections in 100 individuals between 14 years and 24 years old — patterns they verified with data for another 197 individuals in this age group. Along with a decline in association cortex areas after age 14, for example, they saw increased myelination between brain hubs and network hub consolidation during this time. By folding in gene expression data from six post-mortem brain samples, the investigators found that such changes coincided with sites in the brain that express synapse, myelin, and schizophrenia-related genes.

Researchers from the US and Germany delve into the roots of gene body methylation in plants. While most of the plants it analyzed by comparative epigenomics had methylomes resembling Arabidopsis thaliana, the team unearthed a plant lacking gene body methylation: a plant in the Brassicaceae family called Eutrema salsugineum, commonly known as saltwater cress. Through more detailed analyses of that plant, including MethylC sequencing on an additional accession, the group discovered that E. salsugineum is missing the DNA methyltransferase enzyme CMT3. Ties between CMT3 and gene body methylation were further bolstered through the identification of a second plant, Conringia planisiliqua that independently lost the same methyltransferase.