Biology subjects

Louis, A.

Publications and source records attributed to Louis, A..

14 recordsLinked to original sources

bioRxiv2025

Salmonids reveal principles of regulatory evolution following autotetraploidization

Early vertebrate autotetraploidization events may have enabled major innovations by expanding the genetic material for functional diversification, yet their ancient timing obscures how genome doubling reshaped gene regulatory evolution. Salmonids provide a unique window to these mechanisms, because they experienced a comparatively recent autotetraploidization and are earlier in the rediploidization process - which creates new genes and regulatory elements during evolution. Here, using large-scale multiomics spanning embryonic and adult tissues in two salmonids, we investigate gene regulatory evolution following genome doubling and rediploidization, which we show is governed by developmental and tissue-specific context, with a period of maximal constraint at advanced stages of embryogenesis. This work advances understanding of vertebrate genome evolution, while providing an open resource supporting salmonid aquaculture and conservation.

evolutionary biology↗

bioRxiv2025

Temporal dynamics of macrophages transcriptional profiles during zebrafish wound healing

Macrophages participate to wound healing by contributing to host defense and orchestrating inflammation and repair. They adapt dynamically to the wound microenvironment by adopting diverse polarization states, which are determinant of wound outcome, influencing whether healing is successful or becomes chronic. The zebrafish embryo, widely used for live imaging of immune responses, is a powerful model to study macrophage behavior after injury. However, the transcriptional landscape of polarized macrophages in this model during wound healing remains insufficiently characterized. Here, we employ bulk RNA sequencing to characterize macrophage transcriptional programs following tail fin wounding a robust model for studying sterile inflammation. Our findings reveal that zebrafish macrophages undergo large transcriptomic changes along different wound healing phases, particularly between 2 and 5 hours post-amputation, suggesting a fast reprogramming leading to different functional states. We further show that, at 2h, macrophages acquire a pro-inflammatory profile with a gene signature closed to M1 signature. At 5h, macrophages express genes involved in immunoregulation and healing associated with shutoff of pro-inflammatory pathways and the activation of glucose and glycogen metabolism. Finally, we show that macrophage reprogramming becomes deeply attenuated by 29h. Our findings provide a foundation for understanding macrophage polarization in zebrafish, revealing underpinning molecular mechanisms, including both specific and evolutionarily conserved pathways with a potential impact on translational medicine.

immunology↗

bioRxiv2025

Natural protein structures have evolved exceptional robustness to mutations

Protein structures are often conserved across widely divergent sequences, suggesting high mutational robustness. However, how such robustness emerges through evolution, and how it relates to the underlying sequence-structure map, remains poorly understood. In contrast, the mutational profiles (distribution of structures upon point mutation) of RNA secondary structures are well characterised, exhibiting both high mutational robustness and high evolvability through mutational access to diverse folds. The recent revolution in protein structure prediction now enables analagous large-scale analyses for proteins. Here, we use the structure prediction algorithm ESMFold to systematically investigate the mutational profiles of natural, random, and de novo proteins. Unlike RNA, where functional and random sequences share similar mutational profiles, natural proteins are substantially more robust than random amino acid sequences, suggesting an evolutionary drive toward robustness. They also exhibit limited structural variation among close sequence neighbours, potentially constraining access to new folds. Interestingly, many de novo proteins do resemble random sequences in their mutational profiles, with low robustness relative to established proteins. These findings reveal how gene duplication and de novo gene birth follow distinct evolutionary trajectories toward functional proteins and highlight a potential role for large-effect mutations in the emergence of structural complexity.

evolutionary biology↗

bioRxiv2024

Bounding phenotype transition probabilities via conditional complexity

By linking genetic sequences to phenotypic traits, genotype-phenotype maps represent a key layer in biological organisation. Their structure modulates the effects of genetic mutations which can contribute to shaping evolutionary outcomes. Recent work based on algorithmic information theory introduced an upper bound on the likelihood of a random genetic mutation causing a transition between two phenotypes, using only the conditional complexity between them. Here we evaluate how well this bound works for a range of genotype-phenotype maps, including a differential equation model for circadian rhythm, a matrix-multiplication model of gene regulatory networks, a developmental model of tooth morphologies for ringed seals, a polyomino-tile shape model of biological self-assembly, and the HP lattice protein model. By assessing three levels of predictive performance, we find that the bound provides meaningful estimates of phenotype transition probabilities across these complex systems. These results suggest that transition probabilities can be predicted to some degree directly from the phenotypes themselves, without needing detailed knowledge of the underlying genotype-phenotype map.

biophysics↗

bioRxiv2024

Secondary motor cortex tracks decision value and supports behavioral flexibility during non-instructed choice

Optimal decision-making relies on interconnected frontal brain regions, which permit animals to adapt their decisions based on their internal state, experience, and environmental context. Among them, the secondary motor cortex (M2) shows earlier decision-related activity required for sensory-guided action selection. However, the role of M2 in adaptive decision-making in the absence of instructive sensory cues remains unclear. Under such conditions, action-selection relies on abstract representations of actions and their values. Using in vivo microscopy and modeling, we showed that M2 neurons in mice exhibited persistent activity encoding decision values (DV) predicting the probability of action-selection during a non-cue-guided lever task. This was confirmed by the reduced reversal performance upon M2 optogenetic inhibition prior to action-selection. Furthermore, updates in DV determined the rate at which learning is reversed. Together, these results provide strong evidence of the use of DV by M2 to adapt choice in the absence of instructive sensory cues. Declaration of interestsThe authors declare no competing financial interests.

neuroscience↗

bioRxiv2023

CITE-seq reveals inhibition of NF-kB pathway in B cells from vitamin D-treated multiple sclerosis patients

Vitamin D deficiency is a recognized risk factor for multiple sclerosis (MS) and has been associated with disease activity and progression. Vitamin D treatment has emerged as potentially protective, despite conflicting results from randomized controlled trials. Here, we used single-cell RNA-sequencing (scRNA-seq) combined with barcoded antibodies targeting surface markers (CITE-seq) to uncover candidate genes and pathways regulated in PBMC subpopulations from MS patients receiving high-dose vitamin D (n=5) or placebo (n=5). Best candidates were combined with genes involved in immune function and vitamin D metabolism for validation in a new cohort (n=8 in each group) by high-throughput quantitative polymerase chain reaction (HT-qPCR) in FACS-sorted naive CD4, Th1, Th17, Treg, naive CD8, memory and naive B cells, and MAIT cells. CITE-seq revealed no significant changes in the proportions of these subpopulations in response to vitamin D treatment. Out of the 92 candidate genes identified by CITE-seq, we validated differential expression of five genes (UXT, SNRPN, SUB1, GNLY and KLF6) using HT-qPCR. Furthermore, CITE-seq uncovered vitamin D-induced regulation of several pathways in naive and memory B cells, including MAPK, TLR and interleukin pathways, that may contribute to counteract Epstein-Barr virus (EBV)-induced resistance to apoptosis, notably through inhibition of the NF-{kappa}B pathway. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=119 SRC="FIGDIR/small/559400v1_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@1ad28c1org.highwire.dtl.DTLVardef@14ed135org.highwire.dtl.DTLVardef@188fea1org.highwire.dtl.DTLVardef@105353c_HPS_FORMAT_FIGEXP M_FIG C_FIG

genomics↗

bioRxiv2022

Genome structures resolve the early diversification of teleost fishes

Accurate species phylogenies are a prerequisite for evolutionary research. Teleosts are by far the largest and the most diversified group of extant vertebrates, but relationships among the three oldest lineages of extant teleosts remain unresolved. Based on seven high-quality new genome assemblies in Elopomorpha (tarpons, eels), we revisited the topology of the deepest branches of the teleost phylogeny using independent gene sequence and chromosomal rearrangement phylogenomic approaches. These analyses converged to a single scenario that unambiguously places the Elopomorpha and Osteoglossomorpha (bony-tongues) in a monophyletic group sister to all other teleosts, i.e., the Clupeocephala lineage. This finding resolves over 50 years of controversy on the evolutionary relationships of these lineages and highlights the power of combining different levels of genome-wide information to solve complex phylogenies. One-Sentence SummaryWhole-genome analyses place Elopomorpha (tarpons, eels) and Osteoglossomorpha (bony-tongues) as sister groups at the deepest branching of crown teleosts.

evolutionary biology↗

bioRxiv2022

Reconstruction of hundreds of reference ancestral genomes across the eukaryotic kingdom

Ancestral sequence reconstruction is a fundamental aspect of molecular evolution studies, and can trace small-scale sequence modifications through the evolution of genomes and species. In contrast, fine-grained reconstructions of ancestral genome organisations are still in their infancy, limiting our ability to draw comprehensive views of genome and karyotype evolution. Here we reconstruct the detailed gene contents and organisations of 624 ancestral vertebrate, plant, fungi, metazoan and protist genomes, 183 of which are near-complete chromosomal reconstructions. Reconstructed ancestral genomes are similar to their descendants in terms of gene content as expected and agree precisely with reference cytogenetic and in silico reconstructions when available. By comparing successive ancestral genomes along the phylogenetic tree, we estimate the intra- and inter-chromosomal rearrangement history of all major vertebrate clades at high resolution. This freely available resource introduces the possibility to follow evolutionary processes at genomic scales in chronological order, across multiple clades and without relying on a single extant species as reference.

evolutionary biology↗

bioRxiv2022

A high-resolution comparative atlas across 74 fish genomes illuminates teleost evolution after whole-genome duplication

Teleost fishes are ancient tetraploids stemming from an ancestral whole-genome duplication that may have contributed to the impressive diversification of this clade. Whole-genome duplications can occur via self-doubling (autopolyploidy) or via hybridization between different species (allopolyploidy). The mode of tetraploidization conditions evolutionary processes by which duplicated genomes return to a diploid state through meiosis resolution and subsequent genetic divergence (cytological and genetic rediploidization). How teleosts became tetraploid remains unresolved, leaving a fundamental gap to interpret their functional evolution. As legacy of the whole genome duplication, identifying orthologous and paralogous genomic regions across teleosts is challenging, hindering genome-wide investigations into their polyploid history. Here, we combine tailored gene phylogeny methodology together with a state-of-the-art ancestral karyotype reconstruction to establish the first high-resolution comparative atlas of paleopolyploid regions across 74 teleost genomes. We then leverage this atlas to investigate how rediploidization occurred in teleosts at the genome-wide level. We uncover that some duplicated regions maintained tetraploidy for over 60 million years, with three chromosome pairs diverging genetically only after the separation of major teleost families. This evidence suggests that the teleost ancestor was an autopolyploid. Further, we find evidence for biased gene retention along several duplicated chromosomes, contradicting current paradigms that asymmetrical evolution is specific to allopolyploids. Altogether, our results offer novel insights into genome evolutionary dynamics following ancient polyploidizations in vertebrates.

genomics↗

bioRxiv2021

The interplay of supercoiling and thymine dimers inDNA

AO_SCPLOWBSTRACTC_SCPLOWThymine dimers are a major mutagenic photoproduct induced by UV radiation. While they have been the subject of extensive theoretical and experimental investigations, questions of how DNA supercoiling affects local defect properties, or, conversely, how the presence of such defects changes global supercoiled structure, are largely unexplored. Here we introduce a model of thymine dimers in the oxDNA forcefield, parametrised by comparison to melting experiments and structural measurements of the thymine dimer induced bend angle. We performed extensive molecular dynamics simulations of double-stranded DNA as a function of external twist and force. Compared to undamaged DNA, the presence of a thymine dimer lowers the supercoiling densities at which plectonemes and bubbles occur. For biologically relevant supercoiling densities and forces, thymine dimers can preferentially segregate to the tips of the plectonemes, where they enhance the probability of a localized tip-bubble. This mechanism increases the probability of highly bent and denatured states at the thymine dimer site, which may facilitate repair enzyme binding. Thymine dimer-induced tip-bubbles also pin plectonemes, which may help repair enzymes to locate damage. We hypothesize that the interplay of supercoiling and local defects plays an important role for a wider set of DNA damage repair systems.

biophysics↗

bioRxiv2021

Poly-γ-glutamic acid secretion protects Bacillus subtilis from zinc and copper intoxication

Zinc and copper are essential micronutrients that serve as a cofactors for numerous enzymes. However, when present at elevated concentrations, zinc and copper are highly toxic to bacteria. To combat the effects of zinc and copper excess, bacteria have evolved a wide array of defense mechanisms. Here, we show that the Gram positive soil bacterium, Bacillus subtilis, produces the extracellular polymeric substance, poly-gamma-glutamate ({gamma}-PGA) as a protective mechanism in response to zinc and copper excess. Furthermore, we provide evidence that zinc and copper dependent {gamma}-PGA production is independent of the DegS-DegQ two component regulatory system and likely occurs at a post-transcriptional level. These data provide new insight into bacterial metal resistance mechanisms and contribute to our understanding of the regulation of bacterial {gamma}-PGA biosynthesis. ImportanceZinc and copper are potent antimicrobial compounds. As such, bacteria have evolved a diverse range of tools to prevent metal intoxication. Here, we show that the Gram-positive model organism, Bacillus subtilis, produces poly-gamma-glutamic acid ({gamma}-PGA) as a protective mechanism against zinc and copper intoxication and that zinc and copper dependent {gamma}-PGA production occurs by a yet undefined mechanism independent of known {gamma}-PGA regulation pathways.

microbiology↗

bioRxiv2021

Classification of non-coding variants with high pathogenic impact

Whole genome sequencing is increasingly used to diagnose medical conditions of genetic origin. While both coding and non-coding DNA variants contribute to a wide range of diseases, most patients who receive a WGS-based diagnosis today harbour a protein-coding mutation. Functional interpretation and prioritization of non-coding variants represents a persistent challenge, and disease-causing non-coding variants remain largely unidentified. Depending on the disease, WGS fails to identify a candidate variant in 20-80% of patients, severely limiting the usefulness of sequencing for personalised medicine. Here we present FINSURF, a machine-learning approach to predict the functional impact of non-coding variants in regulatory regions. FINSURF outperforms state-of-the-art methods, owing to control optimisation during training. In addition to ranking candidate variants, FINSURF also delivers diagnostic information on functional consequences of mutations. We applied FINSURF to a diverse set of 30 diseases with described causative non-coding mutations, and correctly identified the disease-causative non-coding variant within the ten top hits in 22 cases. FINSURF is implemented as an online server to as well as custom browser tracks, and provides a quick and efficient solution to prioritize candidate non-coding variants in realistic clinical settings.

bioinformatics↗

bioRxiv2020

Synteny-guided resolution of gene trees clarifies the functional impact of whole genome duplications

Whole genome duplications (WGD) have major impacts on the evolution of species, as they produce new gene copies contributing substantially to adaptation, isolation, phenotypic robustness, and evolvability. They result in large, complex gene families with recurrent gene losses in descendant species that sequence-based phylogenetic methods fail to reconstruct accurately. As a result, orthologs and paralogs are difficult to identify reliably in WGD-descended species, which hinders the exploration of functional consequences of WGDs. Here we present SCORPiOs, a novel method to reconstruct gene phylogenies in the context of a known WGD event. WGDs generate large duplicated syntenic regions, which SCORPiOs systematically leverages as a complement to sequence evolution to infer the evolutionary history of genes. We applied SCORPiOs to the 320-million-year-old WGD at the origin of teleost fish. We find that almost one in four teleost gene phylogenies in the Ensembl database (3,391) are inconsistent with their syntenic contexts. For 70% of these gene families (2,387), we were able to propose an improved phylogenetic tree consistent with both the molecular substitution distances and the local syntenic information. We show that these synteny-guided phylogenies are more congruent with the species tree, with sequence evolution and with expected expression conservation patterns than those produced by state-of-the-art methods. Finally, we show that synteny-guided gene trees emphasize contributions of WGD paralogs to evolutionary innovations in the teleost clade.

genomics↗

bioRxiv2018

Chromosome evolution at the origin of the ancestral vertebrate genome

About 450 million years ago, a marine chordate was subject to two successive whole genome duplications (WGDs) before becoming the common ancestor of vertebrates and diversifying into the more than 60,000 species found today. Here, we reconstruct in details the evolution of chromosomes of this early vertebrate along successive steps of the two WGD. We first compared 61 extant animal genomes to build a highly contiguous order of genes in a 326 million years old ancestral Amniota genome. In this genome, we established a well-supported list of duplicated genes originating from the WGDs to link chromosomes in tetrads, a telltale signature of these events. This enabled us to reconstruct a scenario where a pre-vertebrate genome composed of 17 chromosomes duplicated into 34 chromosomes, and was subject to 7 chromosome fusions before duplicating again into 54 chromosomes. After the separation of Agnatha (jawless fish) and Gnathostomata, four more fusions took place to form the ancestral Euteleostomi genome of 50 chromosomes. These results firmly establish the occurrence of the two WGD, resolving in particular the ambiguity raised by the analysis of the lamprey genetic map. In addition, we provide insight into the origin of homologous micro-chromosomes found in the chicken and the gar genomes. This work provides a foundation for studying the evolution of vertebrate chromosomes from the standpoint of a common ancestor, and particularly the pattern of duplicate gene retention and loss that resulted in the gene composition of extant genomes.

genomics↗