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This Week in PNAS: Dec 2, 2009

Using molecular techniques, scientists led by Harvard's Jacob Russell and Corrie Moreau have studied gut microbes in ants to find patterns of symbiosis. Surveying 283 species from 18 of the 21 ant subfamilies, they found "a wealth of bacteria from across the ants." Herbivorous "turtle ants" often had symbiotic bacteria from clades within the Burkholderiales, Pseudomonadales, Rhizobiales, Verrucomicrobiales, and Xanthomonadales. Their results "strongly support the hypothesis that bacteria have facilitated convergent evolution of herbivory across the ants, further implicating symbiosis as a major force in ant evolution," they say in the abstract.

Also appearing in PNAS this week, work from CNRS scientists in Paris have found evidence that endo-siRNAs are involved in heterochromatin formation in somatic tissues in Drosophila. Endogenous siRNAs are a class of small RNAs produced from endogenous double-stranded RNA that have been shown to take part in silencing transposable elements in the Drosophila soma. To test if they played a role in heterochromatin formation, they used the viral suppressors of RNA silencing B2 and P19 and found that both proteins contributed to making the endo-siRNAs inactive. "Strikingly," they write, "B2 or the nuclear form of P19, but not P19, suppressed silencing of heterochromatin gene markers in adult flies, and altered histone H3-K9 methylation as well as chromosomal distribution of histone methyl transferase Su(var)3–9 and Heterochromatin Protein 1 in larvae."

Researchers also checked into whether gene expression patterns in the liver are the result of feeding behavior, circadian rhythms, or both. Studying wild-type and circadian clock-deficient mice, they found that both feeding time and the circadian clock contribute to "rhythmic transcription, thereby highlighting temporal regulation of hepatic transcription as an emergent property of the circadian system," they say.

In work led by Fotis Kafatosa and Kristin Michel at Imperial College London, scientists were able to characterize the transcriptome of circulating hemocytes in the Anopheles gambiae mosquito, the major mosquito carrier of malaria in subSaharan Africa. Using a genome-wide approach, they identified nearly 1,500 transcripts enriched in these immune cells, with many of these genes belonging to innate immune gene families, they say. An RNAi screen found the role that 63 of these genes have in the development of Plasmodium berghei, providing "a molecular comparison of the transcriptome of these cells during malaria infection."

The Scan

Missed Early Cases

A retrospective analysis of blood samples suggests early SARS-CoV-2 infections may have been missed in the US, the New York Times reports.

Limited Journal Editor Diversity

A survey finds low diversity among scientific and medical journal editors, according to The Scientist.

How Much of a Threat?

Science writes that need for a provision aimed at shoring up genomic data security within a new US bill is being questioned.

PNAS Papers on Historic Helicobacter Spread, Brain Development, C. difficile RNAs

In PNAS this week: Helicobacter genetic diversity gives insight into human migrations, gene expression patterns of brain development, and more.