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This Week in PNAS: May 19, 2015

In the early, online edition of the Proceedings of the National Academy of Sciences, researchers from Stanford University describe results from a single-cell RNA sequencing study of the human brain. Using transcriptome profiles for hundreds of individual cells from adult or fetal cortex samples, the team defined cell types based on their shared gene expression clusters, uncovered diverse subtypes within the neuronal cells, and compared transcriptional features in the brain pre- and post-natally. GenomeWeb has more on the study here.

A team from the US and Canada did genome sequencing on Candidatus Hodgkinia bacteria that dwell within the long-lived cicada species Magicicada tredecim. When they compared the genome sequences of this endosymbiont to other insect endosymbionts, the researchers saw signs of lineage splitting within the Ca. Hodgkinia complex, leading to fragmented species that are genetically distinct, yet remain reliant, on one another. "[T]his lineage-splitting process has result[ed] in a complex of Ca. Hodgkinia genomes that are 1.1 [megabase] pairs in length when considered together," the study's authors explain, "an almost 10-fold increase in size from the hypothetical single-genome ancestor."

Finally, the University College London's John Allen reflects on the role that organelles such as chloroplasts and mitochondria play in redox regulation of gene expression and contributions that the organelle's genome retention and colocation makes to this process. "The vital requirement for continued operation of redox regulatory control over gene expression is proposed as the primary reason for the retention of chloroplast and mitochondrial DNA," he concludes. "The redox chemistry of biological energy transduction is then the primary factor determining which genes this DNA contains."