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This Week in PNAS: Apr 2, 2019

Researchers from the Institute of Molecular Systems Biology in Switzerland and the US Department of Energy Joint Genome Institute present a re-written bacterial genome for Caulobacter ethensis-2.0: a chemically synthesized, 785,701 base pair, minimal genome for C. crescentus that contains just 799 encoded genetic features. The team reportedly re-wrote some 123,562 C. crescentus codons and used transposon mutagenesis to functionally test the resulting genome, identifying 432 essential C. crescentus genes. "We present a broadly applicable design-build-test approach to program the most fundamental functions of a cell into a customized genome sequence," the authors write. "By rebuilding the essential genome of Caulobacter crescentus … through the process of chemical synthesis writing, we studied the genetic information content at the level of its essential genes."

An international team led by investigators at Louisiana State University explores the evolutionary history of perching — or "passerine" — birds, based on genetic sequences for birds from 137 families. With a phylogenetic analysis focused on 4,060 ultraconserved element loci in 221 birds from 137 passerine families, calibrated using fossil information, the researchers estimate that perching birds originated in what is now Australia roughly 47 million years ago, before diversifying and spreading around the world. "Although passerine diversification rates fluctuated throughout the Cenozoic [Era], we find no link between the rate of passerine diversification and Cenozoic global temperature," they note, "and our analyses show that the increases in passerine diversification rate we observe are disconnected from the colonization of new continents."

Broad Institute researchers and collaborators at several international centers describe a cerebrospinal fluid-based prion quantification approach aimed at developing therapeutics that dial down native prion protein (PrP) levels in the brain. The team took a crack at quantifying human PrP in cerebrospinal fluid samples with enzyme-linked immunosorbent assay (ELISA), looking at the reliability, stability, and accuracy of the method, as well as the potential confounders and sources of contamination. Based on their results, the authors suggest that ELISA-based analyses of PrP levels in the CSP may serve as a "method for monitoring the effect of a PrP-reducing drug in the [central nervous system], and will facilitate development of prion disease therapeutics with this mechanism of action."