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This Week in PNAS: Jul 3, 2018

Human parvovirus B19 has been associated with humans for a thousand years, according to a new study appearing the Proceedings of the National Academy of Sciences this week. An international team of researchers screened shotgun DNA samples obtained from 1,578 ancient human individuals who lived across Eurasia, Southeast Asia, and Greenland for hints of human parvovirus B19. They identified 20 samples with human parvovirus B19 reads covering more than 30 percent of he virus, indicated that the virus has been associated with humans for at least 7,000 years. Through a phylogenetic analysis, the researchers found that the virus evolved more slowly than thought and traced the most recent common ancestor of B19 to about 12,600 years ago.

A University of Tennessee-led team of researchers examined how different Toxoplasma gondii genotypes emerged in the Northern versus Southern Hemispheres. They tested their suspicion that the rise of agriculture enabled the parasite to adapt to new hosts, like mice and domestic cats. They found that parasite genotypes typically found in the Northern Hemisphere are not or are intermediately virulent in lab mice, while those from the Southern Hemisphere are highly virulent. In a set of simulations, they found that the intermediately virulent T. gondii genotypes have an adaptive advantage in the domestic transmission cycle, and eventually become the dominant type. The researchers also traced the most recent common ancestor of the most widespread type II lineage of T. gondii to the Old World, likely Europe, finding that it spread from there to North America recently.

Researchers from the University of Texas Health Science Center at Houston report that a number of eukaryotes rely on alternative splicing of SKI7/HBS1. Ski7, which is needed for the rapid degradation of mRNAs without stop codons, had been thought to be restricted to Saccharomyces cerevisiae and its relatives as the SKI7 gene and the paralog HBS1 arose through a duplication event in a recent ancestor. But by analyzing transcriptome data from a range of species, the Texas team found that most eukaryotes express Ski7 as an alternative splice isoform from the HBS1 gene.