Caractérisation moléculaire et fonctionnelle de Cif1p, une protéine orpheline impliquée dans le phénomène épigénétique de viabilité de la levure S. pombe en absence de la chaperone calnexine

Le repliement des protéines est un processus cellulaire crucial impliquant plusieurs protéines dont la calnexine, une chaperone du réticulum endoplasmique. Notre laboratoire et un autre groupe avons démontré que la calnexine est essentielle à la viabilité de la levure Schizosaccharomyces pombe. Dans le cadre d’études structure-fonction portant sur cette protéine, nous avons découvert un phénomène permettant la viabilité des cellules en absence de la calnexine. Cet état, nommé Cin pour calnexine independence, est induit par un mutant de la calnexine dépourvu du domaine central hautement conservé (Δhcd_Cnx1p). La caractérisation de l’état Cin a révélé plusieurs caractéristiques particulières telle la dominance, sa transmission de façon non-Mendélienne à la progéniture méïotique et sa transmission par des extraits protéiques dépourvus d’acides nucléiques. Toutes ces propriétés suggèrent donc que l’état Cin est médié via un élément de type prion. Le gène cif1+, pour calnexin independence factor, a été isolé lors de criblages visant à identifier des gènes impliqués dans l’état Cin. Il encode pour une protéine orpheline dont la surexpression induit de façon stable un état de viabilité en l’absence de la calnexine. Cet état diffère génétiquement et phénotypiquement de l’état Cin induit par le mutant Δhcd_Cnx1p préalablement caractérisé, ce qui suggère deux voies parallèles de signalisation du phénomène Cin. Une caractérisation exhaustive de Cif1p a permis de démontrer qu’il ne s’agissait pas du prion responsable de l’état Cin, malgré que cette protéine possède certaines propriétés typiques des prions in vitro. Finalement, Cif1p est une protéine nucléolaire dont la bonne localisation est essentielle à sa capacité à induire l’état Cin. Ceci suggère une interaction entre la fonction essentielle de la calnexine et une fonction exécutée dans le nucléole. Lors d’études visant à élucider la fonction cellulaire de Cif1p, il a été établi qu’elle interagissait avec certaines protéines de la grosse sous-unité du ribosome telle la protéine L3. Cependant, Cif1p ne co-sédimente pas avec des sous-unités ribosomales assemblées, des ribosomes ou des polysomes. De plus, des cellules contenant une délétion génomique de cif1 voient leur contenu en ribosomes perturbé lors de la phase stationnaire. Il semble donc que Cif1p joue un rôle dans la biosynthèse des ribosomes lors de la phase stationnaire. Ce rôle spécifique à cette phase de croissance coincide avec un clivage de la portion N-terminale de Cif1p, clivage qui a lieu lors de l’entrée des cellules en phase stationnaire. De plus, des études effectuées récemment dans notre laboratoire proposent que la calnexine joue un rôle important dans la signalisation de l’apoptose, et ce particulièrement en phase stationnaire. Ainsi, une voie impliquant Cif1p, sa fonction nucléolaire dans la biosynthèse des ribosomes en phase stationnaire, la calnexine et la médiation de l’apoptose semble se dessiner. D’autres travaux, notamment sur la fonction exacte de Cif1p, le rôle de son clivage et les autres composantes impliquées dans le phénomène Cin nous permettront de dessiner un portrait plus complet de cette voie cellulaire inédite.Protein folding is a vital process that involves many proteins of the cell. One of them is calnexin, a chaperone of the endoplasmic reticulum. In the fission yeast Schizosaccharomyces pombe, calnexin is essential for survival of the cells. During structure-function studies on calnexin, our laboratory discovered a phenomenon allowing the viability of cells without this chaperone. This state, designated Cin for Calnexin INdependence, is induced by a calnexin mutant devoid of the highly conserved central domain (Δhcd_Cnx1p). Characterization of the Cin cells showed several exceptional properties such as dominance, non-Mendelian transmission and transmission via cell extracts devoid of nucleic acids of the Cin state. All these observations suggested that the Cin phenomenon is mediated via a prionic element. To identify genes implicated in the Cin state, genetic screens were performed. They led to the identification of the cif1+ gene, for calnexin independence factor. This gene encodes an orphan protein, the overexpression of which stably induces a state of viability in the absence of calnexin. Notably, this state is genetically and phenotypically distinct from the previously isolated Cin state arising from Δhcd_Cnx1p expression. This suggests the presence of two parallel pathways both able to signal the induction of the Cin phenomenon. The exhaustive characterization of Cif1p showed that it is not the prion solely responsible for the Cin state, although it displays prion-like properties in vitro. Finally, nucleolar localization of Cif1p is required to induce the Cincif1 state, thus suggesting an unexpected interaction between the vital cellular role of calnexin and a function of the nucleolus. While investigating Cif1p function in the cell, we observed that it interacts with ribosomal proteins of the large subunit, notably L3, but it does not sediment with assembled ribosomal subunits or whole ribosomes. However, cells containing a genomic deletion of cif1 also have a disrupted ribosome content during stationary phase. Altogether, these results suggest that Cif1p has a role in ribosomal biogenesis during stationary phase. This growth-phase specific role correlates with the occurence during stationary phase of a cleavage in the N-terminal part of Cif1p. Recent studies from our laboratory proposed that calnexin plays an important role in apoptosis signaling, especially in stationary phase. Thus, a pathway implicating Cif1p, its nucleolar function in ribosome biosynthesis in stationary phase, calnexin and apoptosis signaling is starting to emerge. However more studies, notably on the exact function of Cif1p, the role of its cleavage and the other proteins implicated in the Cin state will be necessary to draw the complete scheme of this unprecedented cellular pathway

Bacillus subtilis and Bacillus velezensis population dynamic and quantification of spores after inoculation on ornamental plants

Abstract: Bacillus subtilis and Bacillus velezensis are used in organic agriculture as an alternative to chemical pesticides to fight against phytopathogen organisms. These Gram-positive soil-dwelling bacteria are able to resist harsh conditions and survive by differentiating into endospores. Few studies have examined how bacterial populations change on plants over time, and if they remain active or enter a dormant state. Nonetheless, these characteristics are strikingly important to determine the usage of B. subtilis and B. velezensis and their efficacy in environmental conditions. Here, we investigate the population dynamic on plants of B. subtilis NCIB3610 and B. velezensis QST713 when applied as spores on different ornamental plants. We report that on all plants studied (Echinacea purpurea cv. Salsa red, Echinacea purpurea cv. Fatal attraction and Lavandula angustifolia cv. Hidecote blue) spores rapidly germinated and colonized the rhizoplane, maintaining a relatively low proportion of spores in the population over time, whereas bacterial population on leaves rapidly declined. Bacteria in the surrounding soil did not germinate and persisted as spores. Taken together, these results suggest that only cells found at the rhizosphere remain metabolically active to allow the formation of a lasting relationship with the plant, making possible beneficial effects from the inoculated bacteria.Bacillus subtilis et Bacillus velezensis sont utilisées en agriculture biologique comme alternative aux pesticides chimiques. Ces bactéries Gram-positives vivant dans le sol sont capables de résister à des conditions difficiles et de survivre en se différenciant en endospores. Peu d'études ont examiné comment les bactéries persistent sur les plantes, si elles demeurent actives ou entrent en dormance. Néanmoins, ces caractéristiques sont importantes pour déterminer leur utilisation et leur efficacité dans des conditions environnementales. Nous avons étudié la dynamique de population de B. subtilis NCIB3610 et de B. velezensis QST713 lorsqu'appliquées comme spores sur différentes plantes ornementales. Nous montrons que sur toutes les plantes étudiées (Echinacea purpurea cv. Salsa red, Echinacea purpurea cv. Fatal attraction et Lavandula angustifolia cv. Hidecote blue) les spores ont rapidement germées et colonisées la rhizoplane, maintenant une proportion relativement faible de spores dans la population, alors que la population sur les feuilles a rapidement diminué. Les bactéries présentes dans le sol environnant n'ont pas germé et ont persisté sous forme de spores. Ces résultats suggèrent que seules les bactéries trouvées au niveau des racines restent métaboliquement actives pour permettre la formation d'une relation durable avec la plante, rendant possible les effets bénéfiques des bactéries inoculées

Calnexin Regulates Apoptosis Induced by Inositol Starvation in Fission Yeast

Inositol is a precursor of numerous phospholipids and signalling molecules essential for the cell. Schizosaccharomyces pombe is naturally auxotroph for inositol as its genome does not have a homologue of the INO1 gene encoding inositol-1-phosphate synthase, the enzyme responsible for inositol biosynthesis. In this work, we demonstrate that inositol starvation in S. pombe causes cell death with apoptotic features. This apoptotic death is dependent on the metacaspase Pca1p and is affected by the UPR transducer Ire1p. Previously, we demonstrated that calnexin is involved in apoptosis induced by ER stress. Here, we show that cells expressing a lumenal version of calnexin exhibit a 2-fold increase in the levels of apoptosis provoked by inositol starvation. This increase is reversed by co-expression of a calnexin mutant spanning the transmembrane domain and C-terminal cytosolic tail. Coherently, calnexin is physiologically cleaved at the end of its lumenal domain, under normal growth conditions when cells approach stationary phase. This cleavage suggests that the two naturally produced calnexin fragments are needed to continue growth into stationary phase and to prevent cell death. Collectively, our observations indicate that calnexin takes part in at least two apoptotic pathways in S. pombe, and suggest that the cleavage of calnexin has regulatory roles in apoptotic processes involving calnexin

The impact of poor sleep on cognition and activities of daily living after traumatic brain injury : a review

Background/aim : Patients frequently report sleep disrup-tions or insomnia during their hospital stay, particularlyafter a traumatic brain injury (TBI). The consequences ofthese sleep disturbances on everyday activities are not welldocumented and are therefore not considered in the evalu-ation of independence in activities of daily living (ADLs).The goal of this narrative review is to explore the conse-quences of poor sleep quality on cognition and ADLs inthe acute and subacute stages of a moderate and severeTBI, when patients are in acute care or inpatient rehabili-tation.Methods:We will present an overview of normal sleepand its role in cognitive functioning, and then present thefindings of studies that have investigated sleep characteris-tics in hospital settings and the consequences of sleep dis-turbances on ADLs.Results:During hospitalisation, TBI patients presentsevere sleep disturbances such as insomnia and sleepfragmentation, which are probably influenced by both themedical condition and the hospital or rehabilitation environ-ment. Sleep disruption is associated with several cognitivedeficits, including attention, memory and executive func-tion impairments. Poor quality and/or insufficient quantityof sleep in acute TBI probably affect general functioningand ADLs calling for these cognitive functions.Conclusions and Significance:The cognitive impair-ments present following TBI are probably exacerbated bypoor sleep quality and sleep deprivation during hospitali-sation, which in turn impact ADLs among this popula-tion. Health-care personnel should further consider sleepdisturbances among people with TBI and a sleep protocolshould be established

Galactose Metabolism Plays a Crucial Role in Biofilm Formation by Bacillus subtilis

Galactose is a common monosaccharide that can be utilized by all living organisms via the activities of three main enzymes that make up the Leloir pathway: GalK, GalT, and GalE. In Bacillus subtilis, the absence of GalE causes sensitivity to exogenous galactose, leading to rapid cell lysis. This effect can be attributed to the accumulation of toxic galactose metabolites, since the galE mutant is blocked in the final step of galactose catabolism. In a screen for suppressor mutants restoring viability to a galE null mutant in the presence of galactose, we identified mutations in sinR, which is the major biofilm repressor gene. These mutations caused an increase in the production of the exopolysaccharide (EPS) component of the biofilm matrix. We propose that UDP-galactose is the toxic galactose metabolite and that it is used in the synthesis of EPS. Thus, EPS production can function as a shunt mechanism for this toxic molecule. Additionally, we demonstrated that galactose metabolism genes play an essential role in B. subtilis biofilm formation and that the expressions of both the gal and eps genes are interrelated. Finally, we propose that B. subtilis and other members of the Bacillus genus may have evolved to utilize naturally occurring polymers of galactose, such as galactan, as carbon sources.Molecular and Cellular Biolog

Bacillus subtilis Early Colonization of Arabidopsis thaliana Roots Involves Multiple Chemotaxis Receptors

ABSTRACT Colonization of plant roots by Bacillus subtilis is mutually beneficial to plants and bacteria. Plants can secrete up to 30% of their fixed carbon via root exudates, thereby feeding the bacteria, and in return the associated B. subtilis bacteria provide the plant with many growth-promoting traits. Formation of a biofilm on the root by matrix-producing B. subtilis is a well-established requirement for long-term colonization. However, we observed that cells start forming a biofilm only several hours after motile cells first settle on the plant. We also found that intact chemotaxis machinery is required for early root colonization by B. subtilis and for plant protection. Arabidopsis thaliana root exudates attract B. subtilis in vitro, an activity mediated by the two characterized chemoreceptors, McpB and McpC, as well as by the orphan receptor TlpC. Nonetheless, bacteria lacking these chemoreceptors are still able to colonize the root, suggesting that other chemoreceptors might also play a role in this process. These observations suggest that A. thaliana actively recruits B. subtilis through root-secreted molecules, and our results stress the important roles of B. subtilis chemoreceptors for efficient colonization of plants in natural environments. These results demonstrate a remarkable strategy adapted by beneficial rhizobacteria to utilize carbon-rich root exudates, which may facilitate rhizobacterial colonization and a mutualistic association with the host

Unprecedented tunability of riboswitch structure and regulatory function by sub-millimolar variations in physiological Mg2+

Riboswitches are cis-acting regulatory RNA biosensors that rival the efficiency of those found in proteins. At the heart of their regulatory function is the formation of a highly specific aptamer–ligand complex. Understanding how these RNAs recognize the ligand to regulate gene expression at physiological concentrations of Mg2+ ions and ligand is critical given their broad impact on bacterial gene expression and their potential as antibiotic targets. In this work, we used single-molecule FRET and biochemical techniques to demonstrate that Mg2+ ions act as fine-tuning elements of the amino acid-sensing lysC aptamer's ligand-free structure in the mesophile Bacillus subtilis. Mg2+ interactions with the aptamer produce encounter complexes with strikingly different sensitivities to the ligand in different, yet equally accessible, physiological ionic conditions. Our results demonstrate that the aptamer adapts its structure and folding landscape on a Mg2+-tunable scale to efficiently respond to changes in intracellular lysine of more than two orders of magnitude. The remarkable tunability of the lysC aptamer by sub-millimolar variations in the physiological concentration of Mg2+ ions suggests that some single-aptamer riboswitches have exploited the coupling of cellular levels of ligand and divalent metal ions to tightly control gene expression.Publisher PDFPeer reviewe

Humane Orientation, Work–Family Conflict, and Positive Spillover Across Cultures

Although cross-national work–family research has made great strides in recent decades, knowledge accumulation on the impact of culture on the work–family interface has been hampered by a limited geographical and cultural scope that has excluded countries where cultural expectations regarding work, family, and support may differ. We advance this literature by investigating work–family relationships in a broad range of cultures, including understudied regions of the world (i.e., Sub-Saharan Africa, Southern Asia). We focus on humane orientation (HO), an overlooked cultural dimension that is however central to the study of social support and higher in those regions. We explore its moderating effect on relationships between work and family social support, work–family conflict, and work–family positive spillover. Building on the congruence and compensation perspectives of fit theory, we test alternative hypotheses on a sample of 10,307 participants from 30 countries/territories. We find HO has mostly a compensatory role in the relationships between workplace support and work-to-family conflict. Specifically, supervisor and coworker supports were most strongly and negatively related to conflict in cultures in which support is most needed (i.e., lower HO cultures). Regarding positive spillover, HO has mostly an amplifying role. Coworker (but not supervisor) support was most strongly and positively related to work-to-family positive spillover in higher HO cultures, where providing social support at work is consistent with the societal practice of providing support to one another. Likewise, instrumental (but not emotional) family support was most strongly and positively related to family-to-work positive spillover in higher HO cultures