Explore the vast range of titles available.

The neuronal RNA-binding protein Ptbp2 regulates neuronal differentiation by modulating alternative splicing programs in the nucleus. Such programs contribute to axonogenesis by adjusting the levels of protein isoforms involved in axon growth and branching. While its functions in alternative splicing have been described in detail, cytosolic roles of Ptbp2 for axon growth have remained elusive. Here, we show that Ptbp2 is located in the cytosol including axons and growth cones of motoneurons, and that depletion of cytosolic Ptbp2 affects axon growth. We identify Ptbp2 as a major interactor of the 3’ UTR of Hnrnpr mRNA encoding the RNA-binding protein hnRNP R. Axonal localization of Hnrnpr mRNA and local synthesis of hnRNP R protein are strongly reduced when Ptbp2 is depleted, leading to defective axon growth. Ptbp2 regulates hnRNP R translation by mediating the association of Hnrnpr with ribosomes in a manner dependent on the translation factor eIF5A2. Our data thus suggest a mechanism whereby cytosolic Ptbp2 modulates axon growth by fine-tuning the mRNA transport and local synthesis of an RNA-binding protein. The neuronal RNA-binding protein Ptbp2 is known to regulate neuronal differentiation by modulating alternative splicing. Here, the authors reveal an additional role of cytosolic Ptbp2, which regulates axon growth by fine-tuning the mRNA transport and local synthesis of an RNA-binding protein hnRNP R.

Paramount to human health, symbiotic bacteria in the gastrointestinal tract rely on the breakdown of complex polysaccharides to thrive in this sugar-deprived environment. Gut Bacteroides are metabolic generalists and deploy dozens of polysaccharide utilization loci (PULs) to forage diverse dietary and host-derived glycans. The expression of the multi-protein PUL complexes is tightly regulated at the transcriptional level. However, how PULs are orchestrated at translational level in response to the fluctuating levels of their cognate substrates is unknown. Here, we identify the RNA-binding protein RbpB and a family of noncoding RNAs as key players in post-transcriptional PUL regulation. We demonstrate that RbpB interacts with numerous cellular transcripts, including a paralogous noncoding RNA family comprised of 14 members, the FopS ( f amily o f p aralogous s RNAs). Through a series of in-vitro and in-vivo assays, we reveal that FopS sRNAs repress the translation of SusC-like glycan transporters when substrates are limited—an effect antagonized by RbpB. Ablation of RbpB in Bacteroides thetaiotaomicron compromises colonization in the mouse gut in a diet-dependent manner. Together, this study adds to our understanding of RNA-coordinated metabolic control as an important factor contributing to the in-vivo fitness of predominant microbiota species in dynamic nutrient landscapes. Gut Bacteroides deploy several polysaccharide utilization loci (PULs) to forage diverse dietary and host-derived glycans. Here, the authors identify the RNA-binding protein RbpB and a family of noncoding RNAs as key players in post-transcriptional PUL regulation, further showing that ablation of RbpB in Bacteroides thetaiotaomicron compromises colonization in the mouse gut in a diet-dependent manner.

The human intestine is home to hundreds of bacterial species that collectively modulate, exploit and maintain the host's physiological equilibrium. The dominant phyla in the gut are the Bacteroidota and Bacillota and, among the former, the anaerobe, Gram negative Bacteroides spp. are major human mutualists. B. thetaiotaomicron has over time become a model species of the beneficial microbiota due to its relative ease of cultivation and the development of genetic tools. However, many aspects of this bacterium's physiology and mechanistic details of its interaction with host cells and tissues remain unknown. Notably, the RNA biology of Bacteroides spp. has been largely neglected until recently. This includes small noncoding RNA (sRNAs), which are universal regulators of gene expression in bacteria and are predicted to be present in the hundreds within the Bacteroides genome.This thesis describes the establishment of sequencing-based approaches for the characterization of the gene content and expression profiles of B. thetaiotaomicron. Special attention is dedicated to sRNAs, known in other species for their critical role in quickly adapting to external and intrinsic stimuli and expected to be equally important in Bacteroides due to the dynamic nature of the gut environment. Here, using comparative genomics, we determine the conservation and secondary structures of various B. thetaiotaomicron SRNAs and predict several Bacteroides RNA-binding proteins (RBPs). We then present a strategy for ribosomal RNA (rRNA) depletion from RNA sequencing (RNA-seq) libraries, which allows to increase the informational output obtained from low-input studies such as single-bacteria RNA-seq. Next, a CRISPR interference (CRISPRI) screening approach is established and harnessed to determine the context-dependent functional relevance of sRNAs, revealing regulators of bile stress susceptibility and mucus adherence. Finally, the transcriptomes of both human and B. thetaiotaomicron cells are profiled during colonization of a gut epithelium model, revealing host responses to bacterial presence and Bacteroides metabolic specialization and sRNA expression dynamics. Together, the work reported here expands our knowledge of the B. thetaiotaomicron RNA landscape and introduces several tools and strategies for its investigation.

Plasticity in gene expression allows bacteria to adapt to diverse environments. This is particularly relevant in the dynamic niche of the human intestinal tract; however, transcriptional networks remain largely unknown for gut-resident bacteria. Here we apply differential RNA sequencing (RNA-seq) and conventional RNA-seq to the model gut bacterium Bacteroides thetaiotaomicron to map transcriptional units and profile their expression levels across 15 in vivo-relevant growth conditions. We infer stress- and carbon source-specific transcriptional regulons and expand the annotation of small RNAs (sRNAs). Integrating this expression atlas with published transposon mutant fitness data, we predict conditionally important sRNAs. These include MasB, which downregulates tetracycline tolerance. Using MS2 affinity purification and RNA-seq, we identify a putative MasB target and assess its role in the context of the MasB-associated phenotype. These data—publicly available through the Theta-Base web browser ( http://micromix.helmholtz-hiri.de/bacteroides/ )—constitute a valuable resource for the microbiome community. Integration of differential and conventional RNA sequencing and transposon mutant fitness data for Bacteroides thetaiotaomicron grown under 15 different conditions provides an expression atlas, expands the regulatory RNA repertoire and reveals that the small RNA MasB regulates susceptibility to tetracyclines.

Symbiotic bacteria in the human intestinal microbiota provide many pivotal functions to human health and occupy distinct biogeographic niches within the gut. Yet the molecular basis underlying niche-specific colonization remains poorly defined. To address this, we conducted a time-resolved dual RNA-seq experiment to simultaneously monitor the transcriptional co-adaptations of human commensal and human gut epithelial cells in an anaerobe-epithelium co-culture system. Comparative transcriptomic analysis of mucus-associated versus supernatant populations unveiled small RNAs (sRNAs) that are differentially regulated between spatially segregated subpopulations. Among these, we identified IroR as a key sRNA that facilitates adaptation to the mucus-rich, iron-limiting niche, partly by modulating expression of bacterial capsule genes. This work provides new insights into the spatiotemporal dynamics of gut colonization and underscores a previously underappreciated role for bacterial sRNAs in shaping mutualistic interactions between the human microbiota and the gut epithelium.

Microbiota-centric interventions are limited by our incomplete understanding of the gene functions of many of its constituent species. This applies in particular to small RNAs (sRNAs), which are emerging as important regulators in microbiota species, yet tend to be missed by traditional functional genomics approaches. Here, we establish CRISPR interference (CRISPRi) in the abundant microbiota member Bacteroides thetaiotaomicron for genome-wide sRNA screens. By assessing the abundance of different protospacer-adjacent motifs, we identify the Prevotella bryantii B14 Cas12a as a suitable nuclease for CRISPR screens in these bacteria and generate an inducible Cas12a expression system. Using a luciferase reporter strain, we infer guide design rules and use this knowledge to assemble a computational pipeline for automated gRNA design. By subjecting the resulting guide library to a phenotypic screen, we uncover the previously uncharacterized sRNA BatR to increase susceptibility to bile salts, likely through the regulation of genes involved in Bacteroides cell surface structure. Our study lays the groundwork for unlocking the genetic potential of these major human gut mutualists and, more generally, for discovering hidden functions of bacterial sRNAs.

Gene expression plasticity allows bacteria to adapt to diverse environments, tie their metabolism to available nutrients, and cope with stress. This is particularly relevant in a niche as dynamic and hostile as the human intestinal tract, yet transcriptional networks remain largely unknown in gut Bacteroides spp. Here, we map transcriptional units and profile their expression levels in Bacteroides thetaiotaomicron over a suite of 15 defined experimental conditions that are relevant in vivo, such as variation of temperature, pH, and oxygen tension, exposure to antibiotic stress, and growth on simple carbohydrates or on host mucin–derived glycans. Thereby, we infer stress and carbon source-specific transcriptional regulons, including conditional expression of capsular polysaccharides and polysaccharide utilization loci, and expand the annotation of small regulatory RNAs (sRNAs) in this organism. Integrating this comprehensive expression atlas with transposon mutant fitness data, we identify conditionally important sRNAs. One example is MasB, whose inactivation led to increased bacterial tolerance of tetracyclines. Using MS2 affinity purification coupled with RNA sequencing, we predict targets of this sRNA and discuss their potential role in the context of the MasB-associated phenotype. Together, this transcriptomic compendium in combination with functional sRNA genomics—publicly available through a new iteration of the ′Theta–Base′ web browser (www.helmholtz-hiri.de/en/datasets/bacteroides-v2)—constitutes a valuable resource for the microbiome and sRNA research communities alike.Competing Interest StatementThe authors have declared no competing interest.Footnotes* http://www.helmholtz-hiri.de/en/datasets/bacteroides-v2

Paramount to human health, symbiotic bacteria in the gastrointestinal tract rely on the breakdown of complex polysaccharides to thrive in this sugar-deprived environment. Gut Bacteroides are metabolic generalists and deploy dozens of polysaccharide utilization loci (PULs) to forage diverse dietary and host-derived glycans. The expression of the multi-protein PUL complexes is tightly regulated at the transcriptional level. However, how PULs are orchestrated at translational level in response to the fluctuating levels of their cognate substrates is unknown. Here, we identify the RNA-binding protein RbpB and a family of noncoding RNAs as key players in post-transcriptional PUL regulation. Ablation of RbpB in Bacteroides thetaiotaomicron displays compromised colonization in the mouse gut in a host diet-dependent manner. Current dogma holds that individual PULs are regulated by dedicated transcriptional regulators. We demonstrate that RbpB acts as a global RNA binder that directly interacts with several hundred cellular transcripts. This includes a paralogous noncoding RNA family comprised of 14 members, the FopS (family of paralogous sRNAs) cluster. Through a series of in-vitro and in-vivo assays, we reveal that FopS sRNAs repress the translation of a SusC-like glycan transporter when substrates are limited - an effect antagonized by RbpB. Together, this study implicates RNA-coordinated metabolic control as an important, yet previously overlooked, factor contributing to the in-vivo fitness of predominant microbiota species in dynamic nutrient landscapes.Competing Interest StatementThe authors have declared no competing interest.Footnotes* http://www.ncbi.nlm.nih.gov/geo