Keeping mammalian gastrointestinal (GI) tract communities in balance is crucial for host health maintenance. However, our understanding of microbial communities in the GI tract is still very limited. In this study, samples taken from the GI tracts of C57BL/6 mice were subjected to 16S rRNA gene sequence-based analysis to examine the characteristic bacterial communities along the mouse GI tract, including those present in the stomach, duodenum, jejunum, ileum, cecum, colon and feces. Further analyses of the 283,234 valid sequences obtained from pyrosequencing revealed that the gastric, duodenal, large intestinal and fecal samples had higher phylogenetic diversity than the jejunum and ileum samples did. The microbial communities found in the small intestine and stomach were different from those seen in the large intestine and fecal samples. A greater proportion of Lactobacillaceae were found in the stomach and small intestine, while a larger proportion of anaerobes such as Bacteroidaceae, Prevotellaceae, Rikenellaceae, Lachnospiraceae, and Ruminococcaceae were found in the large intestine and feces. In addition, inter-mouse variations of microbiota were observed between the large intestinal and fecal samples, which were much smaller than those between the gastric and small intestinal samples. As far as we can ascertain, ours is the first study to systematically characterize bacterial communities from the GI tracts of C57BL/6 mice.

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Accumulating evidence highlights the role of histone acetyltransferase GCN5 in the regulation of cell metabolism in metazoans.Here, we report that GCN5 is a negative regulator of autophagy, a lysosome-dependent catabolic mechanism. In animal cells and Drosophila, GCN5 inhibits the biogenesis of autophagosomes and lysosomes by targeting TFEB, the master transcription factor for autophagy-and lysosome-related gene expression. We show that GCN5 is a specific TFEB acetyltransferase, and acetylation by GCN5 results in the decrease in TFEB transcriptional activity. Induction of autophagy inactivates GCN5, accompanied by reduced TFEB acetylation and increased lysosome formation. We further demonstrate that acetylation at K274 and K279 disrupts the dimerization of TFEB and the binding of TFEB to its target gene promoters. In a Tau-based neurodegenerative Drosophila model, deletion of dGcn5 improves the clearance of Tau protein aggregates and ameliorates the neurodegenerative phenotypes. Together, our results reveal GCN5 as a novel conserved TFEB regulator, and the regulatory mechanisms may be involved in autophagy-and lysosome-related physiological and pathological processes. ª 2019 The Authors. Published under the terms of the CC BY NC ND 4.0 license EMBO reports 21: e48335 | 2020 H LC3-II formation in GFP-GCN5-overexpressing HeLa cells. I GFP-p62 levels in HEK293 cells stably expressing GFP-p62. The cells were cultured with GCN5 siRNA with or without CQ. J PDLIM1 and IFT20 protein levels in GCN5 KO HEK293 cells with or without transfection of GFP-GCN5 and addition of CQ. KRepresentative images of mCherry-Atg8a (red) and DAPI (blue) in Drosophila larval fat body in which dGcn5 is overexpressed (OE) or silenced (KD) using the pan-fat body driver (cg-GAL4). Drosophila (cg-GAL4/+) was used as the control (graph represents data from three independent experiments with ≥ 30 cells per condition; mean AE SEM; *P < 0.05, ***P < 0.001, Student's t-test; Scale bars, 10 lm).

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