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Biology subjects

Habermann, B. H.

Publications and source records attributed to Habermann, B. H..

At least 19 recordsLinked to original sources

Predicting the operon structure of the Mycococcus xanthus genome using the novel software DiscOperon

ABSTRACT Motivation: Myxococcus xanthus is a predatory soil bacterium with a large genome of 9.14 MB due to a genome duplication event. While complete genome sequences of M. xanthus are available, gene annotation remains challenging due to its size and the resulting large number of duplicated genes. Operons, so syntenic block of genes that are co-regulated in bacterial genomes, are an important resource to help predict gene function accurately. Results: In order to help improve the annotation of complex genomes such as the one from M. xanthus, we developed a novel operon prediction tool, DiscOperon, which combines gene expression data with homology searches to identify syntenic blocks: Co-expression data of neighbouring genes across the genome are first used to define gene clusters, which are then used to search for conserved syntenic blocks in fully sequenced bacterial genomes using sequence homology searches. This strategy enables DiscOperon to account for gene insertions, rearrangements and deletions, which is its most distinguishing feature. We have tested DiscOperon against ground truths gene pair information on 3 different species from ODB and RegulonDB and compared it to state-of-the-art and still available operon prediction software and we demonstrate its general usability for operon prediction of any bacterial complete genome. We have applied DiscOperon to predict the operons of M. xanthus, which we are making available for the research community. Availability and implementation: DiscOperon is lightweight, user-friendly python tool with minimal dependencies. It is freely available at https://gitlab.com/habermann_lab/discoperon for general usage. Contact: Theo Brunet (theo.brunet@univ-amu.fr); Bianca Habermann (bianca.habermann@univ-amu.fr). Supplementary information: The operon-structured and annotated M. xanthus genome is available from this manuscript, as well as from Zenodo (https://doi.org/10.5281/zenodo.21976167). We furthermore plan to submit the M. xanthus operon information to the operon database OBD.

bioinformatics↗

mitoXplorer 3.0, a web tool for exploring mitochondrial dynamics in single-cell RNA-seq data.

Mitochondria are important eukaryotic organelles, best known for their function in ATP production and in cellular metabolism and signalling. It is widely accepted that their structure, composition and function differ across cell types. However, little is known about mitochondrial variability within the same cell type. To truly understand mitochondrial function and dynamics, we need to study individual cell types, as well as mitochondrial variability on a single-cell level. Based on our mitoXplorer 2.0 web tool, we introduce mitoXplorer 3.0 with new features adapted for analysing single-cell sequencing data, focusing only on mitochondria. We provide a formatting script, scXplorer to generate mitoXplorer 3.0 compatible files for upload. This script creates pseudo-bulk transcriptomes of cell types from scRNA-seq data for differential expression analysis and subsequent mitochondria-centric analysis with mitoXplorer classical interfaces. It also creates a single-cell expression matrix only containing mitochondria-associated genes (mito-genes), which can be analysed for cell-to-cell variability with novel, interactive interfaces created for mitoXplorer 3.0: these new interfaces help to identify sub-clusters of cell types based only on mito-genes and offer in-depth mitochondria-centric analysis of subpopulations. We demonstrate the usability and predictive power of mitoXplorer 3.0 using single-cell transcriptome data from a single-cell study of Spinocerebellar Ataxia Type 1. We identified several mito-processes and mito-genes that are majorly affected in SCA1 Purkinje cells and which might contribute to our understanding of mitochondrial decline and subsequent Purkinje cell loss in this disease. MitoXplorer 3.0 is freely available at https://mitoxplorer3.ibdm.univ-amu.fr.

bioinformatics↗

Titin-dependent biomechanical feedback tailors sarcomeres to specialised muscle functions in insects

Sarcomeres are the contractile units of muscles that enable animals to move. Insect muscles are remarkable examples because they use extremely different contraction frequencies (ranging from [~]1 to 1000 Hz) and amplitudes for flying, walking and crawling. This is puzzling because sarcomeres are built from essentially the same actin-myosin components. We show here that the giant protein titin is the key to this functional specialisation. I-band titin spans and determines the length of the sarcomeric I-band, and occurs in muscle-type-specific isoforms. Surprisingly, it also rules the length of the force-generating myosin filament in a force feedback mechanism, even though it is not present there. We provide evidence for this model and its validity beyond insects. SummaryHere we identified a mechanical mechanism that instructs sarcomeres to fulfill the specific needs of different muscle types.

developmental biology↗

MitoMAMMAL: a genome scale model of mammalian mitochondria predicts cardiac and BAT metabolism

Mitochondria perform several essential functions in order to maintain cellular homeostasis and mitochondrial metabolism is inherently flexible to allow correct function in a wide range of tissues. Dysregulated mitochondrial metabolism can therefore affect different tissues in different ways which presents experimental challenges in understanding the pathology of mitochondrial diseases. System-level metabolic modelling is therefore useful in gaining in-depth insights into tissue-specific mitochondrial metabolism, yet despite the mouse being a common model organism used in research, there is currently no mouse specific mitochondrial metabolic model available. In this work, building upon the similarity between human and mouse mitochondrial metabolism, we have created mitoMammal, a genome-scale metabolic model that contains human and mouse specific gene-product reaction rules. MitoMammal is therefore able to model mouse and human mitochondrial metabolism. To demonstrate this feature, using an adapted E-Flux2 algorithm, we first integrated proteomic data extracted from mitochondria of isolated mouse cardiomyocytes and mouse brown adipocyte tissue. We then integrated transcriptomic data from in vitro differentiated human brown adipose cells and modelled the context specific metabolism using flux balance analysis. In all three simulations, mitoMammal made mostly accurate, and some novel predictions relating to energy metabolism in the context of cardiomyocytes and brown adipocytes. This demonstrates its usefulness in research relating to cardiac disease and diabetes in both mouse and human contexts.

systems biology↗

Fatty Acid Metabolism and The Oxidative Stress Response Support Bacterial Predation

Despite growing awareness of their importance in soil ecology, the genetic and physiological traits of bacterial predators are still relatively poorly understood. In the course of a Myxococcus xanthus predator evolution experiment, we discovered a class of genotypes leading to enhanced predation against diverse species. RNA-seq analysis demonstrated that this phenotype is linked to the constitutive activation of a predation-specific program. Functional analysis of the mutations accumulated across the evolutionary time in a two- component system and Acyl-CoA-manipulating enzymes revealed the critical roles of fatty acid metabolism and antioxidant gene induction. The former likely adapts the predator to metabolites derived from the prey while the latter protects predatory cells from reactive oxygen species (ROS) generated by prey cells under stress and released upon lysis during predation. These findings reveal interesting parallels between bacterial predator-prey dynamics and pathogen-host cell interactions. Significance StatementThis study illuminates the largely unexplored genetic and metabolic strategies used by bacterial predators in soil ecosystems. Through experimental evolution in Myxococcus xanthus, we discovered that more efficient predators accumulate mutations that activate a genetic program for predation. This program simultaneously triggers a metabolic shift favoring fatty acid degradation for energy production and upregulates antioxidant gene expression, enhancing protection against reactive oxygen species generated during prey cell lysis. This adaptive mechanism proves advantageous across a wide range of prey species, suggesting that metabolic adaptation plays a crucial role in the evolutionary trajectory of bacterial predators within their natural ecological niche.

microbiology↗

MechanoProDB: A Web Based Database for Exploring the Mechanical Properties of Proteins

The mechanical stability of proteins is crucial for biological processes. To understand the mechanical functions of proteins, it is important to know the protein structure and mechanical properties. Protein mechanics is usually investigated through force spectroscopy experiments and simulations that probe the forces required to unfold the protein of interest. While there is a wealth of data in the literature on force spectroscopy experiments and steered molecular dynamics simulations of forced protein unfolding, this information is spread and difficult to access by non-experts. Here we introduce MechanoProDB, a novel web-based database resource for collecting and mining data obtained from experimental and computational works. MechanoProDB provides a curated repository for a wide range of proteins, including muscle proteins, adhesion molecules and membrane proteins. The database incorporates relevant parameters that provide insights into the mechanical stability of proteins and their conformational stability such as the unfolding forces, energy landscape parameters and contour lengths of unfolding steps. Additionally, it provides intuitive annotations of the unfolding pathways of each protein, allowing users to explore the individual steps during mechanical unfolding. The user-friendly interface of MechanoProBD allows researchers to efficiently navigate, search and download data pertaining to specific protein folds or experimental conditions. Users can visualize protein structures using interactive tools integrated within the database, such as Mol*, and plot available data through integrated plotting tools. To ensure data quality and reliability, we have carefully manually verified and curated the data currently available on MechanoProDB. Furthermore, the database also features an interface that enables users to contribute new data and annotations, promoting community-driven comprehensiveness. The freely available MechanoProDB aims to streamline and accelerate research in the field of mechanobiology and biophysics by offering a unique platform for data sharing and analysis. MechanoProDB is freely available at https://mechanoprodb.ibdm.univ-amu.fr.

biophysics↗

A mechanically regulated liquid-liquid phase separation of the transcriptional regulator Tono instructs muscle development

Muscle morphogenesis is a multi-step program, starting with myoblast fusion, followed by myotube-tendon attachment and sarcomere assembly, with subsequent sarcomere maturation, mitochondrial amplification and specialisation. The correct chronological order of these steps requires precise control of the transcriptional regulators and their effectors. How this regulation is achieved during muscle development is not well understood. In a genome-wide RNAi screen in Drosophila, we identified the BTB-zinc finger protein Tono (CG32121) as a muscle-specific transcriptional regulator. tono mutant flight muscles display severe deficits in mitochondria and sarcomere maturation, resulting in uncontrolled contractile forces causing muscle atrophy during development. Tono protein is expressed during sarcomere maturation and localises in distinct condensates in flight muscle nuclei. Interestingly, internal pressure exerted by the maturing sarcomeres deforms the muscle nuclei into elongated shapes and changes the Tono condensates, suggesting that Tono senses the mechanical status of the muscle cells. Indeed, external mechanical pressure on the muscles triggers rapid liquid-liquid phase separation of Tono utilising its BTB domain. Thus, we propose that Tono senses high mechanical pressure to in turn adapt muscle transcription specifically at the sarcomere maturation stage. Consistently, tono mutant muscles display specific defects in a transcriptional switch that represses early muscle differentiation genes and boosts late ones. We hypothesise that a similar mechano-responsive regulation mechanism may control the activity of related BTB-zinc finger proteins that, if mutated, can result in uncontrolled force production in human muscle.

developmental biology↗

MitoMouse is a model reconstruction of murine mitochondrial metabolism

Mitochondria, apart from being the powerhouses of our cells, are key players in cellular metabolism and homeostasis. As a consequence, the core bioenergetics and metabolism of mitochondria are well studied considering the role that dysregulated mitochondrial metabolism plays in disease. Flux Balance Analysis, used in conjunction with metabolic model reconstructions is a powerful computational tool that predicts metabolism. The resulting quantitative descriptions of metabolic dysregulation not only allows current hypotheses to be tested in silico, but can also lead to novel model driven hypotheses that can be experimentally verified. Several metabolic reconstructions for human and mouse metabolism exist, but no model specific to mouse mitochondrial metabolism exists. Here, we have created a mouse-specific mitochondrial metabolic model, mitoMouse, which is based on the high-quality human MitoCore mode. MitoMouse contains 390 genes and 445 metabolites involved in 560 unique reactions, is able to model central carbon metabolism and has been extended to contain reduction of the CoQ complex of Oxidative Phosphorylation by the enzyme DHODH. MitoMOuse was validated to accurately model the important metabolic switch involving CoQ reduction resulting from increased malate import, as recently shown in mouse cardiac tissue. We expect this model to be of immense interest and relevance to researchers working on murine mitochondrial metabolism.

systems biology↗

Integrative study of mitochondrial dysfunction in skeletal muscle during pancreatic cancer cachexia

AimsPancreatic Ductal AdenoCarcinoma (PDAC), the most common pancreatic cancer, is a deadly cancer, often diagnosed late and resistant to current therapies. PDAC patients are frequently affected by cachexia characterized by muscle mass and strength loss (sarcopenia) contributing to patient frailty and poor therapeutic response. The objective of this work was to investigate the mechanisms underlying mitochondrial remodeling in the cachectic skeletal muscle, through an integrative study combining functional, morphological and omics-based evaluation of gastrocnemius muscle from genetically-engineered mice developing autochthonous pancreatic tumor and cachexia (KIC GEMM). ResultsKIC cachectic PDAC mice exhibit severe sarcopenia with loss of muscle mass and strength associated with reduced muscle fibers size and induction of protein degradation processes. Mitochondria in PDAC atrophied muscles show reduced respiratory capacities and structural alterations, associated with deregulation of oxidative phosphorylation and mitochondrial dynamics pathways. Beyond the metabolic pathways known to be altered in sarcopenic muscle (carbohydrates, proteins, and redox), lipid and nucleic acid metabolisms are also affected. While the number of mitochondria per cell is not altered, mitochondrial mass is decreased by a factor of 2 and the mitochondrial DNA by a factor of 3, suggesting a defect in mitochondrial genome homeostasis. InnovationMuscle atrophy is associated with strong mitochondrial metabolic defects that are not limited to carbohydrate, protein and redox metabolism, but concern also lipid and nucleic acid metabolism. ConclusionThis work provides a framework to guide towards the most relevant targets in the clinic to limit PDAC-induced cachexia, in particular mitochondrial fatty acid metabolism.

cancer biology↗

The evo-MOTiF pipeline and database for studying protein motif evolution in a structural context

Short linear motifs (SLiMs) in proteins are short functionally independent sequence stretches with a defined function and required for proteins to interact with their environment. Their functional importance makes it interesting to analyse SLiM features further, such as their structural or evolutionary properties, to understand better how SLiMs evolve to shape protein functions. We developed an automated pipeline to analyse features of SLiMs, called evo-MOTiF. This pipeline takes as input a single protein sequence and its associated SLiM(s) and returns a set of scores associated with SLiM features, including their disorder, as well as their overall, positional and amino acid property conservation. To store and easily mine data from the evo-MOTiF pipeline, we developed the evo-MOTiF database, which currently holds [~]9500 motifs, combining data from ELM, PhosphoSitePlus, as well as from cross-linking mass-spectrometry (XL-MS) experiments. The evo-MOTiF database distinguishes itself further by allowing effortless filtering for SLiMs with specific properties, such as disorder, or conservation in evolution and by providing evolutionary, as well as structural information for SLiMs. Preliminary analysis of SLiM features reveals weak negative correlation between disorder and overall, positional, as well as amino acid property conservation, which is in support of previous observations on smaller datasets. The evo-MOTiF pipeline and database are freely available at https://gitlab.com/habermann_lab/slims and http://etnadb.ibdm.univ-mrs.fr/index.php, respectively.

bioinformatics↗

The mitoXplorer 2.0 update: integrating and interpreting mitochondrial expression dynamics within a cellular context

Mitochondria are subcellular organelles present in almost all eukaryotic cells, which play a central role in cellular metabolism. Different tissues, health and age conditions are characterised by a difference in mitochondrial structure and composition. The visual data mining platform mitoXplorer 1.0 was developed to explore the expression dynamics of genes associated with mitochondrial functions that could help explain these differences. It however lacked functions aimed at integrating mitochondria in the cellular context and thus, identifying regulators that help mitochondria adapt to cellular needs. To fill this gap, we upgraded the mitoXplorer platform to version 2.0 (mitoXplorer 2.0). In this upgrade we implemented two novel integrative functions, Network Analysis and the transcription factor- (TF-) Enrichment, to specifically help identify signalling or transcriptional regulators of mitochondrial processes. In addition, we implemented several other novel functions to allow the platform to go beyond simple data visualisation, such as an enrichment function for mitochondrial processes, a function to explore time-series data, the possibility to compare datasets across species as well as an IDconverter to help facilitate data upload. We demonstrate the usefulness of these functions in 3 specific use cases. mitoXplorer 2.0 is freely available without login at http://mitoxplorer2.ibdm.univ-mrs.fr.

bioinformatics↗

Tension-driven multi-scale self-organisation in human iPSC-derived muscle fibers

Human muscle is a hierarchically organised tissue with its contractile cells called myofibers packed into large myofiber bundles. Each myofiber contains periodic myofibrils built by hundreds of contractile sarcomeres that generate large mechanical forces. To better understand the mechanisms that coordinate human muscle morphogenesis from tissue to molecular scales, we adopted a simple in vitro system using induced pluripotent stem cell-derived human myogenic precursors. When grown on an unrestricted two-dimensional substrate, developing myofibers spontaneously align and self-organise into higher-order myofiber bundles, which grow and consolidate to stable sizes. Following a transcriptional boost of sarcomeric components, myofibrils assemble into chains of periodic sarcomeres that emerge across the entire myofiber. By directly probing tension we found that tension build-up precedes sarcomere assembly and increases within each assembling myofibril. Furthermore, we found that myofiber ends stably attach to other myofibers using integrin-based attachments and thus myofiber bundling coincides with stable myofiber bundle attachment in vitro. A failure in stable myofiber attachment results in a collapse of the myofibrils. Overall, our results strongly suggest that mechanical tension across sarcomeric components as well as between differentiating myofibers is key to coordinate the multi-scale self-organisation of muscle morphogenesis.

developmental biology↗

Inferring cell cycle phases from a partially temporal network of protein interactions

The temporal organisation of biological systems into phases and subphases is often crucial to their functioning. Identifying this multiscale organisation can yield insight into the underlying biological mechanisms at play. To date, however, this identification requires a priori biological knowledge of the system under study. Here, we recover the temporal organisation of the cell cycle of budding yeast into phases and subphases, in an automated way. To do so, we model the cell cycle as a partially temporal network of protein-protein interactions (PPIs) by combining a traditional static PPI network with protein concentration or RNA expression time series data. Then, we cluster the snapshots of this temporal network to infer phases, which show good agreement with our biological knowledge of the cell cycle. We systematically test the robustness of the approach and investigate the effect of having only partial temporal information. Our results show for the first time that a temporal network with only partial temporal information, i.e. for some of the PPIs, is sufficient to infer the temporal organization of a system. The generality of the method makes it suitable for application to other, less well-known biological systems for which the temporal organisation of processes plays an important role.

systems biology↗

Evolution of mechanisms controlling epithelial morphogenesis across animals: new insights from dissociation - reaggregation experiments in the sponge Oscarella lobularis.

BackgroundThe ancestral presence of epithelia in Metazoa is no longer debated. Even though Porifera seem to be the best candidates to be the sister group to all other Metazoa, hardly anything is known about the proteins involved in the composition of cell-cell junctions or about the mechanisms that regulate epithelial morphogenetic processes in this phylum. ResultsTo get insights into the early evolution of epithelial morphogenesis, we focused on morphogenic characteristics of the homoscleromorph sponge Oscarella lobularis. Homoscleromorpha are a sponge class with a typical basement membrane and adherens-like junctions unknown in other sponge classes. We took advantage of the dynamic context provided by cell dissociation-reaggregation experiments to explore morphogenetic processes in epithelial cells in an early lineage by combining fluorescent and electronic microscopy observations and RNA sequencing approaches at key time-points of the dissociation and reaggregation processes. ConclusionsOur results show that part of the molecular toolkit involved in the loss and restoration of epithelial features such as cell-cell and cell-matrix adhesion is conserved between Homoscleromorpha and Bilateria, suggesting their common role in the last common ancestor of animals. In addition, Sponge-specific genes are differently expressed during the dissociation and reaggregation processes, calling for future functional characterization of these genes.

evolutionary biology↗

BCL-XL blockage in TNBC models confers vulnerability to inhibition of specific cell cycle regulators

Cell cycle regulators are frequently altered in Triple-Negative Breast Cancer (TNBC). Emerging agents targeting these signals offer the possibility to design new combinatorial therapies. However, preclinical models that recapitulate TNBC primary resistance and heterogeneity are essential to evaluate the potency of these combined treatments. MethodsBioinformatic processing of human breast cancer datasets was used to analyse correlations between expression levels of cell cycle regulators and patient survival outcome. The MMTV-R26Met mouse model of TNBC resistance and heterogeneity was employed to analyse expression and targeting vulnerability of cell cycle regulators in the presence of BCL-XL blockage. Robustness of outcomes and selectivity was further explored using a panel of human breast cancer cells. Alterations of protein expression, phosphorylation, and/or cellular localisation were analysed by western blots, reverse phase protein array, and immunocytochemistry. Bioinformatics was performed to highlight drugs mechanisms of action. ResultsWe report that high expression levels of BCL-XL and specific cell cycle regulators correlate with poor survival outcomes of TNBC patients. Blockage of BCL-XL confers vulnerability to drugs targeting CDK1/2/4, but not FOXM1, CDK4/6, Aurora A and Aurora B, to all MMTV-R26Met and human TNBC cell lines tested. Mechanistically, we show that, co-targeting of BCL-XL and CDK1/2/4 synergistically inhibited cell growth by combinatorial depletion of survival and RTK/AKT signals, and concomitantly restoring FOXO3a tumour suppression actions. This was accompanied by an accumulation of DNA damage and consequently apoptosis. ConclusionsOur studies illustrate the possibility to exploit the vulnerability of TNBC cells to CDK1/2/4 inhibition by targeting BCL-XL. Moreover, they underline that specificity matters in targeting cell cycle regulators for combinatorial anticancer therapies.

cancer biology↗

A Tad-like apparatus is required for contact-dependent prey killing in predatory social bacteria

Myxococcus xanthus, a soil bacterium, predates collectively using motility to invade prey colonies. Prey lysis is mostly thought to rely on secreted factors, cocktails of antibiotics and enzymes, and direct contac with Myxococcus cells. In this study, we show that on surfaces the coupling of A-motility and contact-dependent killing is the central predatory mechanism driving effective prey colony invasion and consumption. At the molecular level, contact-dependent killing involves a newly discovered type IV filament-like machinery (Kil) that both promotes motility arrest and prey cell plasmolysis. In this process, Kil proteins assemble at the predator-prey contact site, suggesting that they allow tight contact with prey cells for their intoxication. Kil-like systems form a new class of Tad-like machineries in predatory bacteria, suggesting a conserved function in predator-prey interactions. This study further reveals a novel cell-cell interaction function for bacterial pili-like assemblages.

microbiology↗

AnnoMiner: a new web-tool to integrate epigenetics, transcription factor occupancy, and transcriptomics data to predict transcriptional regulators

Gene expression regulation requires precise transcriptional programs, led by transcription factors in combination with epigenetic events. Recent advances in epigenomic and transcriptomic techniques provided insight into different gene regulation mechanisms. However, to date it remains challenging to understand how combinations of transcription factors together with epigenetic events control cell-type specific gene expression. We developed the AnnoMiner web-server and introduce an innovative and flexible way to annotate and integrate epigenetic, and transcription factor occupancy data. First, AnnoMiner annotates user-provided peaks with gene features. Second, AnnoMiner can integrate genome binding data from two different transcriptional regulators together with gene features. Third, AnnoMiner offers to explore the transcriptional deregulation of 10 genes nearby a user-provided peak. AnnoMiners fourth function performs transcription factor or histone mark enrichment analysis for user-provided gene lists by utilizing hundreds of public, high-quality datasets from ENCODE for the model organisms human, mouse, Drosophila and C. elegans. Thus, AnnoMiner can predict transcriptional regulators for a studied process without the strict need for chromatin data from the same process. We compared AnnoMiner to existing tools and experimentally validated several transcriptional regulators predicted by AnnoMiner to indeed contribute to muscle morphogenesis in Drosophila. AnnoMiner is freely available at http://chimborazo.ibdm.univ-mrs.fr/AnnoMiner/.

bioinformatics↗

The Hippo pathway controls myofibril assembly and muscle fiber growth by regulating sarcomeric gene expression

Skeletal muscles are composed of gigantic cells called muscle fibers, packed with force-producing myofibrils. During development the size of individual muscle fibers must dramatically enlarge to match with skeletal growth. How muscle growth is coordinated with growth of the contractile apparatus is not understood. Here, we use the large Drosophila flight muscles to mechanistically decipher how muscle fiber growth is controlled. We find that regulated activity of core members of the Hippo pathway is required to support flight muscle growth. Interestingly, we identify Dlg5 and Slmap as regulators of the STRIPAK phosphatase, which negatively regulates Hippo to enable post-mitotic muscle growth. Mechanistically, we show that the Hippo pathway controls timing and levels of sarcomeric gene expression during development and thus regulates the key components that physically mediate muscle growth. Since Dlg5, STRIPAK and the Hippo pathway are conserved a similar mechanism may contribute to muscle or cardiomyocyte growth in humans.

developmental biology↗