Biology subjects

Dieu, M.

Publications and source records attributed to Dieu, M..

16 recordsLinked to original sources

bioRxiv2026

Mitochondrial dysfunction as a hallmark of brain senescence in telomerase-deficient mice

Neurodegenerative diseases, including Alzheimer's disease (AD), are strongly associated with aging. However, the molecular mechanisms underlying pathological brain aging remain incompletely understood. In this study, we used a mouse model of telomere attrition, a major driver of cellular senescence, to perform an unbiased analysis of how telomere-driven senescence affects cellular physiology and contributes to processes relevant to neurodegenerative conditions. After validating the presence of senescence hallmarks in telomerase-deficient brains, we characterized their transcriptomic and proteomic profiles. Mitochondrial function and associated energy metabolism emerged as the major dysregulated pathways, driven predominantly by proteomic rather than transcriptomic changes. Functional biochemical analyses on isolated brain mitochondria demonstrated impaired electron transport chain (ETC) complex activity and reduced energetic status, despite preserved ETC complex integrity and mitochondrial content. Further analyses in senescent primary neurons indicated an accumulation of dysfunctional mitochondria, characterized by increased reactive oxygen species (ROS) production and reduced ATP levels, although basal cellular respiration was maintained. At the tissue level, these alterations were associated with moderate reductions in neuronal density in the subiculum and cortical layer V, indicating region-specific vulnerability rather than widespread neurodegeneration. We propose that a major consequence of telomere dysfunction associated with pathological brain aging is the downregulation of mitochondrial activity, which contributes to the selective vulnerability of specific brain regions. These findings highlight mitochondrial pathways as attractive targets for interventions aimed at preserving brain health during aging.

neuroscience↗

bioRxiv2026

Identification of the cellular transcription factor KLF16 as a novel repressive epigenetic repressor of HIV-1 transcription

Despite antiretroviral therapy, human immunodeficiency virus type 1 (HIV-1) persists in latently-infected cells through epigenetic and transcriptional mechanisms. Latency-reversing agents have failed clinically, partly due to incomplete understanding of HIV-1 latency reversal. Here, using DNA-affinity capture and mass spectrometry on the HIV-1 5 long terminal repeat (5LTR) enhancer-core promoter, we identify KLF16 (Kruppel-like Factor 16) as a novel regulator of HIV-1 gene expression. KLF16 binds to the HIV-1 5LTR in vivo at Sp1 binding sites, and KLF16 depletion reactivates latent HIV-1 in T-lymphoid and monocytic cell models. Mechanistically, KLF16 represses HIV-1 transcription by competing with Sp1 for promoter binding and by recruiting the Sin3A/HDAC1 and HP1/Suv39H1 repressive epigenetic complexes. KLF16 is also upregulated in CD4+ T cells from ART-treated people with HIV-1 upon T-cell activation. Additionally, All-Trans retinoic acid (ATRA) reactivates latent HIV-1 in myeloid cells, partly by downregulating KLF16. These findings establish KLF16 as a novel transcriptional repressor of HIV-1, identifying it as a potential promising therapeutic target for cure strategies. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=136 SRC="FIGDIR/small/722432v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@1611026org.highwire.dtl.DTLVardef@16b5eaforg.highwire.dtl.DTLVardef@153b11org.highwire.dtl.DTLVardef@1d90330_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2025

A subset of type 4 secretion system effectors of Brucella spp. associates to outer membrane vesicles

The establishment of a replicative niche in the hostile environment of the host presents an enormous challenge for pathogens. Intracellular pathogens such as Brucella spp., the Gram-negative causative agents of Brucellosis, must subvert diverse host functions to ensure survival and replication. One of the key adaptations to achieve this is the translocation of effector proteins into host cells via its type 4 secretion system (T4SS), a key virulence factor. But effector identification in Brucella is particularly challenging, as previously identified effectors lack a conserved translocation signal, exhibit variable requirements for translocation, and in some cases appear to be translocated in a T4SS-independent manner. Here, we demonstrate that a subset of previously described T4SS effector proteins associates with outer membrane vesicles (OMVs) in different Brucella species. Most of these effector proteins encode predicted signal peptides for periplasmic export or transmembrane domains. Among them, BspC and VceA carry functional signal peptides that direct their export into the periplasm in a Sec-dependent manner. From the periplasm these proteins are subsequently secreted into the extracellular milieu, likely via the formation and release of OMVs. Our findings provide new insights into protein secretion by Brucella, suggesting that OMVs may represent an alternative secretion pathway to the T4SS.

microbiology↗

bioRxiv2025

Unraveling the pathway of Copper Delivery to Cytochrome c oxidases in the Free-Living Bacterium Caulobacter vibrioides

Copper (Cu) is an essential micronutrient that serves as a cofactor for many enzymes but becomes toxic when present in excess. In most bacteria, CopA-like P1B-type ATPases mediate Cu detoxification by exporting cytoplasmic Cu to the periplasm or extracellular environment. In this study, we show that Caulobacter vibrioides lacks a canonical CopA-like ATPase but encodes a single FixI/CcoI-type Cu-transporting ATPase, previously implicated in Cu delivery to the cbb{square}-type cytochrome c oxidase (Cox) in species such as Rhodobacter capsulatus. C. vibrioides harbors two terminal cytochrome c oxidases in its cytoplasmic membrane: an aa{square}-type and a cbb{square}-type Cox. We also demonstrate that the activity of cbb{square}-Cox requires the FixI-type Cu transporter and the periplasmic Cu chaperone PccA. In contrast, aa{square}-Cox activity depends on PccA and the inner membrane-bound protein CtaG. Since the mechanism of Cu acquisition for aa{square}-Cox remains largely unknown, we conducted a genetic screen and identified a novel outer membrane TonB-dependent receptor (TccA) that is specifically required for aa{square}-Cox function. We also showed that cbb{square}-Cox is upregulated under microaerobic conditions, possibly such as those encountered on solid media where O2 diffusion is limited. Under normoxic conditions, the expression and the activity of cbb{square}-Cox decrease, and aa{square}-Cox becomes the predominant terminal oxidase. These findings demonstrate that C. vibrioides differentially utilizes its Cox enzymes in response to O2 availability and relies on a distinct Cu trafficking pathway for their maturation, including an outer membrane component that has not been previously described in bacterial Cu homeostasis.

microbiology↗

bioRxiv2025

Upregulation of the AcrAB2NodT efflux pump confers antibiotic resistance at the cost of collateral metal sensitivity

Bacterial resistance to antibiotics (AB) such as {beta}-lactams, fluoroquinolones, and aminoglycosides often emerges through mutations that alter AB targets, reduce membrane permeability, or increase the activity of AB-modifying enzymes and efflux pumps. Yet the physiological costs associated with AB resistance remain poorly understood. In Caulobacter vibrioides, a {Delta}tipR mutant that which constitutively upregulates the RND pump AcrAB2nodT, displays heightened sensitivity to copper (Cu), revealing a physiological vulnerability driven by the energetic burden imposed by excessive efflux activity. Deletion of acrAB2nodT in the {Delta}tipR background restored Cu resistance to wild-type levels, confirming the role of pump overexpression in metal sensitivity. Morphological and microscopy analyses revealed that pump overexpression leads to cell envelope defects and compromised fitness. To disentangle the effects of pump abundance from efflux activity, we engineered an AcrB2 transport-impaired mutant. This variant also rescued Cu resistance, demonstrating that high expression and active transport contribute to the observed toxicity. Notably, this sensitivity was not limited to Cu; the {Delta}tipR mutant also exhibited increased susceptibility to other transition metals, including zinc (Zn), nickel (Ni) and cadmium (Cd), suggesting a broader vulnerability linked to metal stress. Mechanistically, pump overexpression depleted the proton motive force, reduced ATP levels, and impaired motility, all of which are essential for Cu stress adaptation. This physiological tradeoff highlights the importance of precise efflux regulation and reveals a potential therapeutic vulnerability: targeting the cost of pump upregulation could enhance the efficacy of antimicrobial treatments. ImportanceWhile efflux pumps primarily protect bacteria from AB, their excessive activity can impose a fitness cost. This study underscores a crucial tradeoff between resistance and cellular fitness by connecting Cu sensitivity to heightened AcrAB2NodT efflux pump expression in Caulobacter vibrioides. This work challenges the assumption that more efflux always benefits the cell and shows that unregulated pump activity can undermine survival under metal stress. These findings broaden our understanding of bacterial stress physiology and suggest new ways to combat antimicrobial resistance by targeting the hidden costs of resistance mechanisms. Understanding this balance between resistance and fitness opens new perspectives for combination therapy against multidrug-resistant bacteria.

microbiology↗

bioRxiv2025

An Early Olfactory Transcriptomic Signature of Tauopathy: Gbp2b Emerges as a Candidate Biomarker of Tau-Driven Neuroinflammation

Olfactory dysfunction is increasingly recognized as an early feature of neurodegenerative diseases such as Alzheimers disease. PS19 mice, a well-established tauopathy model, exhibit hallmarks of tau pathology--including hyperphosphorylated tau and pretangle formations--in various regions of the olfactory system. Notably, very recent data demonstrated that aberrantly hyperphosphorylated tau (pTau) was detected as early as 1.5 months of age in the olfactory epithelium (OE). This region contains olfactory sensory neurons projecting to the olfactory bulb (OB), where similar pTau pattern was also observed at this early stage. By 6 months, tau pretangles were evidenced in higher olfactory areas such as the piriform and entorhinal cortices. Given the early involvement of the OE and OB in tau pathology, we performed transcriptomic analyses at 3, 6, and 9 months to investigate the molecular pathways underlying tau pathology in these olfactory regions. Due to the OEs peripheral location and anatomical accessibility, we also aimed in that respect to identify potential early biomarkers of tauopathy. The hippocampus, a key brain region affected in Alzheimers disease and related disorders, was included in the analysis as a comparative reference due to its known vulnerability and clinical relevance. Our analyses revealed region- and age-specific gene expression changes in PS19 mice. Functional enrichment analyses indicated a temporal progression of molecular alterations associated with tau pathology. We identified a subset of genes differentially expressed across different time points and/or regions. Among these, Gbp2b emerged as a particularly promising early biomarker candidate for tauopathy in the OE, showing consistent upregulation across tau pathological stages and brain regions. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=152 SRC="FIGDIR/small/662324v1_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@17148c1org.highwire.dtl.DTLVardef@5fa7dborg.highwire.dtl.DTLVardef@51e21org.highwire.dtl.DTLVardef@1fd4302_HPS_FORMAT_FIGEXP M_FIG Created in BioRender. Kienlen-Campard, P. (2025) https://BioRender.com/k7xoypd C_FIG

neuroscience↗

bioRxiv2025

Atypical features of the disordered N-terminal region of a bacterial outer membrane copper transporter.

Metals like copper (Cu), zinc, and nickel exhibit dual nature, necessitating a tight regulation of their cellular homeostasis to meet physiological demands while preventing toxicity. In bacteria, metal homeostasis involves inner membrane (IM) P-type ATPases and ABC transporters, envelope-spanning tripartite efflux pumps, and outer membrane (OM) pore-forming proteins. Four decades ago, the OM {beta}-barrel protein PcoB was shown to provide an additional layer of Cu resistance in an Escherichia coli strain isolated from the gut of swine fed with Cu supplements. Interestingly, most PcoB homologs contain a poorly conserved disordered N-terminal domain (NTD) rich in histidine (His) and methionine (Met) residues, which are commonly associated with Cu coordination in cuproproteins. This suggests a potential role for the NTD in PcoB-mediated copper efflux. We previously demonstrated that the free-living bacterium Caulobacter vibroides primarily relies on PcoB for Cu homeostasis. Here, we show that the NTD of C. vibroides PcoB is critical for PcoB function and stability, tolerating the swapping with the poorly conserved E. coli PcoB NTD and significant truncations. Unexpectedly, the predicted signal peptide (SP) was dispensable, challenging traditional concepts of protein translocation mechanisms. Moreover, the PcoB NTD plays a surprising role in stabilizing the periplasmic multicopper oxidase PcoA, encoded within the same operon as PcoB, highlighting a new role for an intrinsically disordered region (IDR). ImportanceBacterial copper (Cu) homeostasis is essential for survival in fluctuating environments, yet the role of single outer membrane proteins in this process remains poorly characterized. Our study reveals that the intrinsically disordered N-terminal region of the {beta}-barrel protein PcoB in Caulobacter vibroides plays a critical role in Cu efflux and PcoB stability. Remarkably, this region harbors an atypical signal peptide and contributes to the stability of the periplasmic multicopper oxidase PcoA, suggesting a novel regulatory function for an intrinsically disordered region. These findings challenge existing paradigms of protein targeting and homeostasis, with broad implications for understanding bacterial adaptation to stress.

molecular biology↗

bioRxiv2024

Role of a TonB-dependent receptor and an oxygenase in iron-dependent copper resistance in Caulobacter crescentus

Copper (Cu) is potentially threatening for living organisms owing to its toxicity at high concentrations, requiring the onset of diverse detoxification strategies to maintain fitness. We previously showed that the environmental conditions modulate the response of the oligotrophic alphaproteobacterium Caulobacter crescentus to Cu excess. In the present study, we investigated the role of the Fe-importing TonB-dependent receptor (TBDR) CciT and its partner, CciO, a 2-oxoglutarate/Fe2+-dependent oxygenase, in Cu resistance. CciT is specifically involved in Cu resistance in both rich and poor media. Using inductively coupled plasma optical emission spectrometry, we found that under Cu stress, the cellular Cu content is reduced by overexpression of cciT, while Fe content increases. Mutations of the three known Fe-importing TBDRs reveal that CciT is the primary Fe importer in these conditions and the only TBDR required for Cu resistance. In addition, the extracellular Fe concentration is positively correlated with the cellular Fe content and negatively correlated with the cellular Cu content, resulting in the protection of the cells against Cu excess. The operon organization of cciT and cciO is highly conserved across bacteria, indicating a functional link between the two proteins. Deletion of cciT, cciO, or both genes leads to similar Cu sensitivity. Catalytic mutations in CciT and CciO also result in Cu sensitivity. While CciO is not required for Cu and Fe transport, its precise function remains unknown. Overall, this study provides new insights into the role of Fe uptake in Cu resistance, emphasizing the critical influence of environmental conditions on bacterial physiology. ImportanceCopper is an essential metal for many living organisms, as it helps to drive crucial chemical reactions. However, when present in excess, copper turns toxic due to its high reactivity with biological molecules. Bacteria may encounter excess copper in various environments, such as polluted soils, agricultural copper treatments, and within the vacuoles of infected macrophages. In this study, we investigated the copper response in the environmental bacterium Caulobacter crescentus. Our findings reveal that environmental iron levels play a critical role in copper resistance, as increased iron prevents cellular copper accumulation and toxicity. We identified two essential proteins, CciT and CciO, that are involved in iron transport, providing protection against copper excess.

microbiology↗

bioRxiv2024

A lipid transport Mla Pqi Chimeric system is essential for Brucella abortus survival in macrophages

The envelope of diderm bacteria comprises of an inner membrane (IM) and an outer membrane (OM). Several pathways have been recently identified that facilitate the transport of phospholipids between the two membranes in Escherichia coli, including maintaining OM lipid asymmetry (Mla) and paraquat inducible (Pqi) systems. In this study, we report the identification and the characterization of a complex named Mpc in the intracellular pathogen Brucella abortus. Mpc is conserved in numerous species of Hyphomicrobiales and exhibits homology to both the Mla and Pqi systems. Mpc is essential for bacterial growth under conditions of envelope stress and for survival within macrophages during the early stages of infection. Analyses of protein-protein interactions and structural predictions indicate that the Mpc complex bridges IM to OM. The absence of this system results in an altered lipid composition of the OM vesicles, supporting the fact that Mpc plays a role in the transport of lipids between membranes. The discovery of a novel lipid trafficking system enhances the diversity and complexity of known lipid trafficking systems within diderm bacteria.

microbiology↗

bioRxiv2024

TamL is a key player of the outer membrane homeostasis in Bacteroidetes.

In Proteobacteria, the outer membrane protein TamA and the inner membrane-anchored protein TamB form the Translocation and Assembly Module (TAM) complex, which facilitates the transport of autotransporters, virulence factors, and likely lipids across the two membranes. In Bacteroidetes TamA is replaced by TamL, a TamA-like lipoprotein with a lipid modification at its N-terminus that likely anchors it to the outer membrane. This structural difference suggests that TamL may have a distinct function compared to TamA. However, the role of TAM in bacterial phyla other than Proteobacteria remains unexplored. Our study aimed to elucidate the functional importance of TamL in Flavobacterium johnsoniae, an environmental Bacteroidetes. Unlike its homologues in Proteobacteria, we found that TamL and TamB are essential in F. johnsoniae. Through genetic, phenotypic, proteomic, and lipidomic analyses, we discovered that TamL depletion severely compromises outer membrane integrity, as evidenced by reduced cell viability, altered cell shape, increased susceptibility to membrane-disrupting agents, and elevated levels of outer membrane lipoproteins. Notably, we did not observe any impact on outer membrane lipid composition. Via pull-down protein assays, we confirmed that TamL interacts with TamB in F. johnsoniae, likely forming the TAM complex. Furthermore, our in silico analysis revealed that the presence of TamL and TamB monocistronic genes is a shared genetic feature among Bacteroidetes members, including the human pathogen Capnocytophaga canimorsus where we also confirmed the essentiality of the TamL and TamB homologs. To our knowledge, this study is the first to provide functional insights into a TAM subunit beyond Proteobacteria. SignificanceIn Proteobacteria, the outer membrane (OM) protein TamA forms with the inner membrane (IM)-anchored protein TamB the Translocation and Assembly Module Complex (TAM). which contributes to efficient biogenesis of the OM. In Bacteroidetes TamA is replaced by TamL, a TamA-like lipoprotein of unknown role. In this work, we studied TamL in the Bacteroidetes Flavobacterium johnsoniae. We found that TamL and TamB are essential for cell viability, and that TamL depletion disrupts outer membrane stability, increases outer membrane vesicle size, and lead to higher sensitivity to OM stressors. These findings highlight TamL critical role in maintaining OM structure in Bacteroidetes. To our surprise, we also identified multiple TamL, TamB and TamA homologs in Bacteroidetes. Altogether, our findings extend the current knowledge on TAM and provide novel insights into a field of research barely investigated outside Proteobacteria.

microbiology↗

bioRxiv2024

Novel insights into Emx2 and Dmrta2 cooperation during cortex development and evidence for Dmrta2 function in choroid plexus

Early dorsal telencephalon development is coordinated by an interplay of transcription factors that exhibit a graded expression pattern in neural progenitors. How they function together to orchestrate cortical development remains largely unknown. The Emx2 and Dmrta2 genes encode TFs that are expressed in a similar caudomedialhigh/ rostrolaterallowgradient in the ventricular zone of the developing dorsal telencephalon with, in the medial pallium, Dmrta2 but not Emx2 expressed in the developing choroid plexus. Their constitutive loss has been shown to impart similar cortical abnormalities, and their combined deletion exacerbates the phenotypes, suggesting possible cooperation during cortex development. In this study, we utilized molecular and genetic approaches to dissect how Emx2 functions with Dmrta2 during cortical development. Our results show that while they regulate a similar set of genes, their common direct targets are limited but include key regulators of cortical development. Identification of the interaction partners of Emx2 suggests that it coordinates with the LIM-domain binding protein Ldb1 to execute the activation and repression of some of its downstream targets. Finally, while Emx2 is known to suppress choroid plexus development, we also provide evidence that Dmrta2 is in contrast required for choroid plexus since in its absence in medial telencephalic progenitors, mice develop hydrocephalous postnatally, a phenotype that appears to be due to a compromised cytoarchitecture. Together, these data indicate that Emx2 and Dmrta2 have similar but also distinct functions in telencephalon development and provide the first insights into Emx2 mechanism of action. SIGNIFICANCE STATEMENTEmx2 and Dmrta2 encode transcription factors that generate similar phenotypes upon their loss in the developing cortex suggesting possible cooperation. Here we explored how Emx2 functions with Dmrta2 during cortical development. Results obtained indicate that Emx2 directly regulates with Dmrta2 only a few genes, some coding for key cortical determinants and that Emx2 utilizes the Ldb1 cofactor for the regulation of some of its targets. Results also suggest that, unlike Emx2 which suppresses choroid plexus development, Dmrta2 is required for choroid plexus as its loss in medial telencephalic progenitors leads to hydrocephalus. Together, our results reveal that Emx2 and Dmrta2 have similar but also distinct functions during telencephalon development and provide novel insights into the mechanism of action of Emx2.

neuroscience↗

bioRxiv2024

Evidence that Dmrta2 acts as a transcriptional repressor of Pax6 in murine cortical progenitors and identification of a mutation crucial for DNA recognition associated with microcephaly in human

Dmrta2 (also designated Dmrt5) is a transcriptional regulator expressed in cortical progenitors in a caudomedialhigh/rostrolaterallow gradient with important roles at different steps of cortical development. Dmrta2 has been suggested to act in cortex development mainly by differential suppression of Pax6 and other homeobox transcription factors such as the ventral telencephalic regulator Gsx2, which remains to be fully demonstrated. Here we have addressed the epistatic relation between Pax6 and Dmrta2 by comparing phenotypes in mutant embryos or embryos overexpressing both genes in various allelic combinations. We showed that Dmrta2 cooperates with Pax6 in the maintenance of cortical identity in dorsal telencephalic progenitors and that it acts as a transcriptional repressor of Pax6 to control cortical patterning. Mechanistically, we show that in P19 cells, Dmrta2 can act as a DNA-binding dependent repressor on the Pax6 E60 enhancer and that a point mutation that affects its DNA binding properties leads to agenesis of the corpus callosum, pachygyria, and the absence of the cingulate gyrus. Finally, we provide evidence that Dmrta2 binds to the Zfp423 zinc finger protein and that it enhances its ability to recruit the NurD repressor complex. Together, our results highlight the importance and conserved function of Dmrta2 in cortical development and provide novel insights into its mechanism of action. SIGNIFICANCE STATEMENTCorticogenesis is controlled by an array of transcription factors that coordinate neural progenitor self-renewal and differentiation to generate correct cortical cell number and diversity. However, how this complex array of transcription factors works in concert to regulate this delicate process remains largely unknown. Here we provide important insights into the mechanism of action of Dmrta2 by demonstrating that it cooperates with the transcription factor Pax6 to define the pallium-subpallium boundary and that it acts by repressing it, likely via the recruitment of Zfp423 and the NurD repressor complex, to control cortical patterning. Our data also reveal that a point mutation that affects its DNA binding causes cortical abnormalities in human, further highlighting its importance in cortex development.

neuroscience↗

bioRxiv2024

LolA and LolB are conserved in Bacteroidetes and are crucial for gliding motility and Type IX secretion.

In Gram-negative bacteria, lipoproteins are major components of the outer membrane (OM) where they play a variety of roles, from the involvement in membrane biogenesis to virulence. Bacteroidetes, a widespread phylum of Gram-negative bacteria, including free-living organisms, commensals and pathogens, encode an exceptionally high number of outer membrane lipoproteins. These proteins are crucial in this phylum mainly because they are key components of SUS-like nutrient acquisition systems as well as of the Type 9 secretion (T9SS) and gliding motility machineries. The transport of lipoproteins to the OM has mainly been studied in E. coli and relies on the Lol system, composed of the inner membrane extraction machinery LolCDE, the periplasmic carrier LolA and the OM lipoprotein LolB. While most Lol proteins are essential and conserved across Gram-negative bacteria, to date, no LolB homologs have been identified outside of {gamma}- and {beta}-proteobacteria. How lipoproteins reach and are inserted in the OM of Bacteroidetes is not known. Here we identified LolB homologs in Bacteroidetes and disclosed the co-existence of several LolA and LolB in several species. We provide evidence that one LolA (LolA1) and one LolB (LolB1) of F. johnsoniae are devoted to targeting gliding and T9SS lipoproteins to the OM. A proteomic analysis of the OM composition of the lolA1 and lolB1 mutants supports this evidence. Furthermore, we show that, while LolB1 and LolA1 have conserved functions in Bacteroidetes, they are functionally different from their E. coli counterparts. We also show that surface lipoprotein transport is LolA and LolB independent. Finally, the finding that, in the absence of LolA and LolB homologs, lipoproteins still localize to the OM, suggests the presence in Bacteroidetes of yet unidentified LolAB-alternative lipoprotein transport pathways. In conclusion, Bacteroidetes have evolved different and more complex lipoprotein transport pathways than other Gram-negative bacteria and further research is required to uncover their complexity. SignificanceIn Gram-negative bacteria, lipoproteins are key components of the outer membrane (OM), essential for functions like membrane biogenesis and virulence. Bacteroidetes, a widespread phylum, encode a high number of OM lipoproteins crucial for nutrient acquisition, Type IX secretion, and gliding motility. While lipoprotein transport in E. coli depends on the Lol system, LolB homologs were previously unidentified outside {gamma}- and {beta}-proteobacteria. Here we identify LolB homologs in Bacteroidetes, revealing the co-existence of multiple LolA and LolB proteins in various species. In F. johnsoniae, LolA1 and LolB1 specifically target gliding and Type 9 secretion system lipoproteins to the OM. Despite this, lipoproteins still localize to the OM without LolA and LolB, suggesting alternative transport pathways. These findings indicate that Bacteroidetes have evolved more complex lipoprotein transport mechanisms than other Gram-negative bacteria, requiring further research to fully understand them.

microbiology↗

bioRxiv2024

In-depth study of MPV17: a molecular travel unveiling a mitochondrial calcium regulation function

Mitochondrial DNA depletion syndromes are severe genetic disorders associated with mutations in a variety of genes including MPV17, encoding a protein of the inner mitochondrial membrane with an unclear function. In this study, using BioID technology, we identified MPV17 interacting partners among which proteins from the MICOS complex. However, MPV17 knockout did not impact mitochondrial ultrastructure, but led to increased mitochondria-derived vesicles formation and altered mitochondrial permeability transition pore. Furthermore, MPV17 KO cells exhibited higher mitochondrial calcium levels and reactive oxygen species, leading to mtDNA degradation, a phenomenon prevented by blocking mitochondrial calcium entry or treating cells with antioxidant. We thus propose a function for MPV17 as a potential additional member of the mitochondrial permeability transition pore, whereas in the absence of the protein, the build-up of calcium inside the mitochondria would lead to mtDNA degradation caused by increased oxidative damages.

cell biology↗

bioRxiv2022

Reactive oxygen species-based sensing by a single chemoreceptor controls bacterial chemotaxis to copper

Chemotaxis is a widespread strategy used by unicellular and multicellular living organisms to maintain their fitness in stressful environments. We previously showed that bacteria can trigger a negative chemotactic response to a copper (Cu)-rich environment. Cu ions toxicity on bacterial cell physiology has been mainly linked to mismetallation events and ROS production, although the precise role of Cu-generated ROS remains largely debated. Here, we found that the cytoplasmic Cu ions content mirrors variations of the extracellular Cu ions concentration and triggers a dose-dependent oxidative stress, which can be abrogated by superoxide dismutase and catalase overexpression. The inhibition of ROS production in the cytoplasm not only improves bacterial growth but also impedes Cu-chemotaxis, indicating that ROS derived from cytoplasmic Cu ions mediate the control of bacterial chemotaxis to Cu. We also identified the Cu chemoreceptor McpR, which binds Cu ions with low affinity, suggesting a labile interaction. In addition, we demonstrate that the cysteine 75 and histidine 99 within the McpR sensor domain are key residues in Cu chemotaxis and Cu coordination. Finally, we discovered that in vitro both Cu(I) and Cu(II) ions modulate McpR conformation in a distinct manner. Overall, our study provides mechanistic insights on a redox-based control of Cu chemotaxis, indicating that the cellular redox status can play a key role in bacterial chemotaxis.

microbiology↗

bioRxiv2018

An interdisciplinary study around the reliquary of the late cardinal Jacques de Vitry

The reliquary of Jacques de Vitry, a prominent clergyman and theologian in the early 13th century, has experienced several transfers over the last centuries, which seriously question the attribution of the remains to the late Cardinal. Uncertainty about the year of his birth poses an additional question regarding his age at death in 1240. The reliquary, located in the Saint Marie dOigines church, Belgium, was reopened in 2015 for an interdisciplinary study around his relics as well as the Treasure of Oignies, a remarkable cultural heritage notably built from Jacques de Vitrys donation. Anthropological, isotopic and genetic analyses were performed independently on the remains found in the reliquary. Results of the analyses provided evidence that the likelihood that these remains are those of Jacques de Vitry is very high: the remains belong to the same human male individual and the historical tradition about his age is confirmed. In addition, a separate relic (left tibia) was analysed and found to match with the remains of the reliquary (right tibia). The unique Jacques de Vitrys mitre, made of parchment, was sampled non-destructively and the extracted parchment collagen was analysed by a proteomic method in order to determine the animal species. The results showed that, surprisingly, not all parts of the mitre were made from the same species. All together, these findings are expected to fertilize knowledge carried by historical tradition around the relics of Jacques de Vitry and his related cultural heritage.

genetics↗