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This Week in PNAS: Feb 17, 2015

In a paper appearing in the early, online edition of the Proceedings of the National Academy of Sciences, researchers from the Institute for Systems Biology, the University of California, San Diego, the National Institute of Mental Health Intramural Research Program, and elsewhere describe a role for rare changes to genes involved in neuronal excitability in bipolar disorder. The team performed genome sequencing on 200 individuals from 41 families with higher-than-usual rates of the psychiatric disorder, focusing its analysis on genes and pathways with potential roles in neuronal function or disease risk. Results of the analysis pointed to an over-representation of rare variants in neuronal ion genes and other neuronal excitability genes in individuals with bipolar disorder.

A team from Yale University, Boston Children's Hospital, and other centers in the US considered the interplay between genes and environment during post-natal mammalian intestine development for another PNAS study. By tracking gene expression and microbial community membership in colon and small intestine samples from wild type and genetically modified mice from dozens of litters across various post-natal developmental stages, the researchers saw transcriptional shifts associated with birth and with events such as weaning. "These transitions reflect both developmental and environmentally induced changes in intestinal gene expression," the study's authors say, noting that their findings highlight contributions involving developmental processes, gut microbes, and innate immune signaling pathways.

Finally, an international group led by investigators in Canada and Sweden used whole-genome sequencing to look at the advent of polyploidy and the early events that followed in an angiosperm plant called Capsella bursa-pastoris, which is believed to have undergone genome duplication during the last 100,000 years to 300,000 years, leaving it with a tetraploid genome. The researchers generated genome assemblies for C. bursa-pastoris and a related plant called C. orientalis, comparing them to a C. rubella reference genome. Their results indicate that the tetraploid plant experienced a dip in selection strength and efficiency after hybridization, rather than widespread gene loss, allowing many inactivating mutations inherited by parent plants to remain in the genome.