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This Week in PNAS: May 5, 2009

In early online publication, a collaboration between Northwestern University Feinberg School of Medicine, the University of Chicago, and Cold Spring Harbor Laboratory defined the transcriptome of human CD34+ hematopoietic stem-progenitor cells, finding that early hematopoiesis is an "orchestrated process" involving more than half the human genes distributed in various functions. In other work, a consortium performed two GWAS and a meta-analysis of bipolar disorder in people of European ancestry, finding strong associations on 1p31.1, 3p21, and 5q15. These regions have genes implicated in cell cycle, neurogenesis, neuroplasticity, and neurosignaling.

In this week's issue of PNAS, University of Michigan scientists used phylogenetic analysis to study the evolution of piRNA clusters in mammals, finding that cluster expansion is driven by positive selection. Out of 140 rodent piRNA clusters, 14 were acquired after rats and mice diverged and another 44 after rodents and primates diverged, and most clusters came about by ectopic recombination "via insertions of long sequences that were mediated by flanking chromosome-specific repetitive elements," they write.

Also in this issue, chemists looked at disulfide-rich peptides in venom using ETD mass spectrometry. "The various species of marine cone shells have alone been estimated to produce [greater than] 50,000 distinct peptide venoms," they write in the abstract. Their analysis revealed full sequences for 31 peptide toxins from the crude venom of the cone snail, Conus textile.

Johns Hopkins' Joshua Mendell led work published this week that found that contact between cells activates miRNA biogenesis. As mammalian and Drosophila cell lines grew to increasing density, miRNA biogenesis was globally activated, leading to increased levels of mature miRNA, stronger target repression, enhanced processing of miRNAs by Drosha, and more efficient formation of RNA-induced silencing complexes, they say.

The Scan

Tens of Millions Saved

The Associated Press writes that vaccines against COVID-19 saved an estimated 20 million lives in their first year.

Supersized Bacterium

NPR reports that researchers have found and characterized a bacterium that is visible to the naked eye.

Also Subvariants

Moderna says its bivalent SARS-CoV-2 vaccine leads to a strong immune response against Omicron subvariants, the Wall Street Journal reports.

Science Papers Present Gene-Edited Mouse Models of Liver Cancer, Hürthle Cell Carcinoma Analysis

In Science this week: a collection of mouse models of primary liver cancer, and more.