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This Week in PNAS: Feb 24, 2015

In the early, online edition of the Proceedings of the National Academy of Sciences, an international research team catalogs the microRNAs present in more than a dozen human cell types. The researchers did short RNA sequencing on more than 1,300 samples representing 13 tissue types. Using this data, they tallied up more than 3,700 miRNAs not described previously, classifying new and known miRNAs based on their tissue-specificity. From sequence conservation, meanwhile, the study's authors determined that that nearly all of the novel miRNAs were specific to the primate lineage.

University of Washington researchers used mutation rate reporter strains to try to understand why genes encoded on the lagging strand of Bacillus subtilis DNA are more prone to accumulating mutations than are leading strand genes. Results from their experiments suggest that this lagging strand mutagenesis reflects transcription-coupled nucleotide excision repair activity by a Y-family polymerase called PolY1. "[G]ene orientation, together with transcription, can cause differential activities of repair mechanisms," the study's authors write, "specifically increasing mutagenesis in lagging-strand genes."

Finally, Stanford University's Ash Alizadeh and colleagues explore the early mutational events associated with follicular lymphoma. The team first did exome sequencing on purified B cells obtained from tumors from 28 individuals with follicular lymphoma, together with matched germline DNA from T cells intermingling with the tumors. After identifying 284 genes that appeared prone to mutation in the tumors, the investigators looked at their mutation frequency in the disease in more detail using targeted sequencing in samples from 110 more follicular lymphoma patients. Using 59 biopsy samples obtained over time from 22 individuals, they also saw mutation patterns pointing to diminished antigen presentation during early stages of the disease.