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This Week in PNAS: Sep 19, 2017

In the early, online edition of the Proceedings of the National Academy of Sciences, a team from Japan describes endosymbiotic Nardonella bacteria that contribute to the formation of the thick, crusty cuticles surrounding hard beetles. The researchers began by sequencing larval bacteriomes from four weevil species, using the reads to put together genome assemblies for Nardonella symbionts in these weevils. Despite the diminutive size of these streamlined genomes, their genomic, transcriptomic, and functional experiments suggest Nardonella genomes house a partial tyrosine synthesis pathway that appeared to function in concert with weevil host genes to produce the tyrosine precursor used for the beetles' cuticle formation. "Our finding highlights an impressively intimate and focused aspect of the host-symbiont metabolic integrity via streamlined evolution for a single biological function of ecological relevance," the authors write.

Researchers from the University of California, San Francisco, the Hotchkiss Brain Institute, and elsewhere explore the consequences of different IDH gene alterations in low-grade glioma. Using exome sequencing, the team compared mutation and copy number patterns in IDH1- and/or IDH2-mutant tumors at diagnosis and recurrence in 50 low-grade glioma cases. Half a dozen recurrent tumors contained IDH1 amplifications or deletions, the authors found. Their cell culture and xenograft tumor experiments suggest that these IDH1 copy number changes lead to clonal expansion, epigenetic changes, and a higher-grade tumor at the time of recurrence. 

Finally, a team from Hungary, Belgium, and the US looks at the effects of vitamin A metabolite-sensing retinoid X receptor deletion in myeloid cells. Based on RNA sequence, chromatin immunoprecipitation sequencing, and other experiments in a mouse model of non-small cell lung carcinoma, the researchers saw an uptick in lung cancer metastasis when the retinoid X receptor was missing from the myeloid lineage. "Overall," the authors say, "our results identify [retinoid X receptor] as a regulator in the myeloid cell-assisted metastasis process and establish lipid-sensing nuclear receptors in the microenvironmental regulation of tumor progression."