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This Week in PNAS: Jul 6, 2010

In the PNAS Early Edition this week, investigators at the University of Connecticut report their analysis of trans-splicing in Drosophila using data from paired-end mRNA deep sequencing of interspecies hybrids. The team writes that they didn't find evidence "for the existence of chimeric RNAs generated by trans-splicing of RNAs transcribed from distant genomic loci," and suggest that "experimental artifacts are the source of most, if not all, apparent chimeric RNA products." Overall, the team identified 80 genes that they suggest "appear to undergo trans-splicing between homologous alleles."

In another paper published online in advance, Stanislas Leibler and Edo Kussell examine individual histories — "temporal sequences of all reproduction events and phenotypic changes of individuals and their ancestors" — in order to quantify selection within phenotypically heterogeneous populations in varied experimental settings. The authors suggest that "reproduction events alone ... may be sufficient to accurately measure selection," and that the measure is "applicable in a wide range o biological systems."

A trio of researchers from Rockefeller University in New York show that "promoter melting triggered by bacterial RNA polymerase occurs in three steps," which they deduced using models of Thermus aquatics RNA polymerase holoenzyme and promoter RNA complexes. First, the authors write, double-stranded DNA melts while the non-template strand interacts with RNAP. Next, "DNA scrunches into RNA polymerase and the downstream base pairs sequentially open to form the transcription bubble, which results in strain build up." And finally, "downstream dsDNA bending relieves the strain as R•Po forms," the team writes.

And in this week's issue of PNAS, an international research team presents their draft sequence of the mushroom Coprinopsis cinerea genome, which they assembled into 13 chromosomes. The team analyzed genome-wide meiotic recombination and transcription patterns, and compared C. cinerea with Laccaria bicolor, a symbiotic basidiomycete, whose genomes "share extensive regions of synteny," they write. "The chromosome assembly of C. cinerea is an essential resource in understanding the evolution of multicellularity in the fungi," the authors suggest.

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.