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This Week in PNAS: Nov 24, 2009

In the Proceedings of the National Academy of Sciences this week, scientists at Rockefeller University studied how stress affects histone marks in the hippocampus in mice. Previous work has associated histone H3 methylation at lysines 4, 9, and 27 with transcription, heterochromatin formation, and lowered transcription, respectively. Using antibodies to these marks, they found that "acute stress increased the levels of H3K9 tri-methylation (H3K9me3) in the dentate gyrus and CA1, while it reduced levels of H3K9 mono-methylation (H3K9me1) and H3K27 tri-methylation (H3K27me3) in the same regions, and had no effect on levels of H3K4 tri-methylation (H3K4me3)." The results, they write in the paper, "show a pattern of changes remarkable for their rapidity, magnitude, and regional specificity."

Harvard Medical School's Norbert Perrimon and Laurence Rahme are lead authors on work that shows that a genetic variant can help bacterial infections lead to stem-cell mediated intestinal cancer. Using Drosophila as a model, they discovered that infection by Pseudomonas aeruginosa ultimately leads to apoptosis of enterocytes, the largest class of differentiated intestinal cells, they say. This in turn makes stem cells and stem cell progenitors proliferate. "However, we find that this homeostatic mechanism can lead to massive over-proliferation of intestinal cells when infection occurs in animals with a latent oncogenic form of the Ras1 oncogene."

Researchers at the Max Planck Institute for Molecular Genetics and the Institute Gustave-Roussy have used next-gen sequencing to study mutations in E. coli. Sequencing several E. coli genomes from colonies of cells subjected to chemical mutagenesis, they saw a "strikingly nonrandom distribution" of mutations. The results, they say, show how "analysis of the molecular records left in the genomes of the descendants of an individual mutagenized cell allows for genome-scale observations of fixation and segregation of mutations, as well as recombination events, in the single genome of their progenitor."

Wayne State University scientists led phylogenetic analysis of human, elephant, tenrec, and mouse genomes to look for patterns of adaptive evolution in aerobic energy metabolism genes. Scanning substitution rates for about 6,000 genes, they found that elephant and human showed much slower nucleotide substitution rates than tenrec and mouse, but more adaptively evolved genes. Taking into account absolute brain size and brain oxygen consumption, they saw that "adaptively evolved aerobic energy metabolism genes were most evident in the elephant lineage and next most evident in the human lineage."

The Scan

Booster for At-Risk

The New York Times reports that the US Food and Drug Administration has authorized a third dose of the Pfizer-BioNTech SARS-CoV-2 vaccine for people 65 and older or at increased risk.

Preprints OK to Mention Again

Nature News reports the Australian Research Council has changed its new policy and now allows preprints to be cited in grant applications.

Hundreds of Millions More to Share

The US plans to purchase and donate 500 million additional SARS-CoV-2 vaccine doses, according to the Washington Post.

Nature Papers Examine Molecular Program Differences Influencing Neural Cells, Population History of Polynesia

In Nature this week: changes in molecular program during embryonic development leads to different neural cell types, and more.