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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

Pig Organ Transplants Considered

The Wall Street Journal reports that the US Food and Drug Administration may soon allow clinical trials that involve transplanting pig organs into humans.

'Poo-Bank' Proposal

Harvard Medical School researchers suggest people should bank stool samples when they are young to transplant when they later develop age-related diseases.

Spurred to Develop Again

New Scientist reports that researchers may have uncovered why about 60 percent of in vitro fertilization embryos stop developing.

Science Papers Examine Breast Milk Cell Populations, Cerebral Cortex Cellular Diversity, Micronesia Population History

In Science this week: unique cell populations found within breast milk, 100 transcriptionally distinct cell populations uncovered in the cerebral cortex, and more.