Institut de Biologie Paris-Seine

Telomeres cap the extremities of linear chromosomes and prevent their detection as DNA damage. Telomere uncapping poses a profound threat to genome integrity, yet the immediate consequences of transient uncapping remain unclear. In Saccharomyces cerevisiae, the Cdc13-Stn1-Ten1 complex limits resection, preventing DNA damage checkpoint activation. Here, using the temperature-sensitive cdc13-1 allele, we demonstrate that transient telomere uncapping rapidly induces extensive genomic rearrangements despite a functional DNA damage checkpoint. Two distinct rearrangement signatures are observed in surviving cells: recombination of the subtelomeric region mostly involving the Y' elements, and massively elongated telomeres up to 10 kb, a ~ 30-fold increase. Long-read sequencing evidences Y' element losses/amplifications, terminal duplications, and telomeric-circle-driven amplifications of telomere repeats. Rearrangements unfold over multiple generations and require the homologous recombination factor Rad52, the Polδ subunit Pol32, and partially Rad51 and Rad59. Remarkably, survivors with elongated telomeres demonstrate a robust Rad52-dependent resistance to subsequent telomere uncapping. Our findings provide novel insights into the consequences of transient telomere uncapping for genome stability, a process that might contribute to subtelomere and telomere dynamics and evolution.

Arterial stiffening is influenced by the organization of focal adhesions in vascular smooth muscle cells (VSMCs). We investigated the contribution of αv integrins to both arterial wall stiffness (Young's modulus measured by echography) and VSMC stiffness (assessed by atomic force microscopy). Mice with VSMC-specific deletion of αv integrins (αvSMKO) were compared with controls at baseline and following angiotensin II infusion. Unstimulated cultured αv-deficient (αv-KD) VSMCs exhibited higher stiffness than controls, with a further increase after angiotensin II. To interpret AFM measurements performed at shallow indentation depths, we developed a computational model of VSMC nanoindentation. Simulations showed that higher apparent Young's moduli at shallow indentation fall within the experimental range of αv-KD cells. These cells also displayed enhanced actin polymerization, further amplified by angiotensin II through the formation of cortical F-actin. In vivo, arterial pressure and wall elastic modulus were similar between αvSMKO and control mice at baseline and after angiotensin II, despite αvSMKO mice exhibiting lower elastin and higher collagen content under angiotensin II. Together, these findings indicate that the comparable increase in arterial stiffness observed in αvSMKO mice under angiotensin II is driven primarily by elevated VSMC stiffness resulting from cortical actin redistribution, which outweighs extracellular matrix changes.

Reward processes have traditionally been ascribed to dopamine (DA)-associated circuits. While external stimuli, such as food and drugs of abuse, are activators of DA-neuron activity, growing evidence indicates that interoceptive signals also play a critical role. Among these, the gut-brain vagal axis has emerged as a key regulator, although its precise contribution to mesolimbic DA signaling and behavior remains unclear. Here, we combine complementary ex vivo and in vivo approaches across multiple scales to show that gut-brain vagal tone is essential for gating mesolimbic DA system activity and functions, modulating DA-dependent molecular and cellular processes, and scaling both food- and drug-induced reinforcement. These findings challenge the traditional brain-centric view of reward processing, supporting a more integrated model in which vagus-mediated interoceptive signals intrinsically shape motivation and reinforcement. By uncovering the influence of gut-brain vagal communication on DA functions, this work provides insights into the neurobiology of adaptive and maladaptive reward, with broad relevance for eating disorders and addiction.

β-1,3-glucans are multifaceted molecules, playing a key role in aquatic ecosystems where they store atmospheric CO2, as well as in human health, where they help fight pathogens and have anticancer properties. Until now, no role other than sugar storage had been attributed to β-1,3-glucans in algae. We show here that in Chlamydomonas reinhardtii, β-1,3-glucans control aggregation, a collective behavior in response to stress. We have identified the enzymes specifically involved in β-1,3-glucan synthesis and degradation during aggregation. The transcriptome of β-1,3-glucan-induced aggregation revealed an early effect of this elicitor. A comparative genomic analysis allowed us to envisage a potential role for β-1,3-glucans in the transition to multicellularity in Volvocales. The finding of the function of β-1,3-glucans in the stress response of the unicellular model organism Chlamydomonas sheds light into their mode of action. This is particularly relevant given their potential roles combatting pathogenic fungi in plants and animals.

Summary A key limitation in cancer transcriptomics is the lack of accompanying genomic profiling such as whole-genome sequencing (WGS) or copy number alteration (CNA) data. Here we address this by showing that RNA-seq alone can be used to infer chromosomal aberrations and identify biologically meaningful patterns in lung cancer. Through a large-scale meta-analysis of publicly available RNA-seq datasets from non-small cell lung cancer (NSCLC), small cell lung cancer (SCLC), and matched controls, we reconstructed large scale CNA profiles and identified deletions in 3p, 9p, and 17p as the most frequent genomic events. Validation against paired WGS data confirmed a high degree of accuracy for RNA-seq-based inference. Our analyses revealed that while deletion-associated transcriptional heterogeneity exists, approximately 25% of differentially expressed genes were shared across all three deletion classes, indicating a conserved oncogenic program in lung cancer. Enrichment analysis linked these shared genes to pathways governing cell division, DNA replication, and extracellular matrix organization, while deletion-specific effects reflected disruption of tumor suppressor pathways, notably p53 signaling in 17p-deleted tumors, leading to deregulation of NOS2 and PLOD2. Integrating gene-level expression data, we identified both shared and deletion-specific biomarkers: TPX2 was consistently overexpressed across all deletion groups, while PTPRZ1 and CLDN9 were uniquely associated with del3p and del9p, respectively. Experimental validation in lung cancer cell lines confirmed these predictions, particularly the upregulation of CLDN9 in del9p carriers. By demonstrating that RNA-seq data can capture large-scale chromosomal events and reveal their transcriptional consequences, this study establishes an efficient framework for genomic inference and biomarker discovery, introducing CLDN9 as a novel, deletion-specific marker with potential prognostic and therapeutic value for 9p-deleted lung cancers.

Abstract Primary cilia are tiny cellular protrusions of nearly every vertebrate cell controlling multiple cellular processes, such as proliferation, differentiation, migration etc. Their dysfunction results in severe human diseases collectively referred to as ciliopathies. Remarkably, many ciliopathies are associated with increased programmed cell death (PCD). However, it is largely unknown how primary cilia regulate PCD. In in vitro (murine and human cells) and in vivo ( Xenopus laevis and mouse) models, we observed elevated PCD in the absence of the ciliopathy protein RPGRIP1L. Mechanistically, our data elucidated that RPGRIP1L controls PCD by governing the activity of the ciliary proteasome. By using super-resolution microscopy, we first showed that the apoptosis inducer MOAP1 localises to primary cilia. Furthermore, our investigations revealed that RPGRIP1L controls PCD via the degradation of MOAP1 by the ciliary proteasome. Based on our finding that two more ciliopathy proteins, TCTN1 and CEP290, modulate PCD via regulating the activity of the ciliary proteasome, we suggest that the proteasomal degradation of MOAP1 represents a general mechanism by which primary cilia control PCD.

Understanding how collective neuronal activity in the brain orchestrates behavior is a central question in integrative neuroscience. Addressing this question requires models that can offer a unified interpretation of multimodal data. In this study, we jointly examine video-recordings of zebrafish larvae freely exploring their environment and calcium imaging of the Anterior Rhombencephalic Turning Region (ARTR) circuit, which is known to control swimming orientation, recorded in vivo under tethered conditions. We show that both behavioral and neural data can be accurately modeled using a Hidden Markov Model (HMM) with three hidden states. In the context of behavior, the hidden states correspond to leftward, rightward, and forward swimming. The HMM robustly captures the key statistical features of the swimming motion, including bout-type persistence and its dependence on bath temperature, while also revealing inter-individual phenotypic variability. For neural data, the three states are found to correspond to left- and right-lateral activation of the ARTR circuit, known to govern the selection of left vs. right reorientation, and a balanced state, which likely corresponds to the behavioral forward state. To further unify the two analyses, we exploit the generative nature of the HMM, using neural sequences to generate synthetic swimming trajectories, whose statistical properties are similar to the behavioral data. Overall, this work demonstrates how state-space models can be used to link neuronal and behavioral data, providing insights into the mechanisms of self-generated action.

ABSTRACTDespite being one of the few bona fide plant tyrosine phosphatases, the Arabidopsis thalianaRhizobiales‐like phosphatase 2 (RLPH2) has no known substrates. Utilizing phospho‐proteomics, we identified the activation loop phospho‐tyrosine of several A. thaliana D‐group mitogen‐activated protein kinases (MPKs) as potential RLPH2 substrates. All Arabidopsis D‐group MPKs possess a TDY activation loop phosphorylation motif, whereas other MPKs (Groups A, B, and C) contain a TEY motif. Our findings reveal that RLPH2 has a strong preference for aspartate (D) in the TXY motif, providing specificity for RLPH2 to exclusively target and dephosphorylate the D‐group MPKs. Additionally, D‐group MPKs contain a unique activation loop insertion that conforms to a protein phosphatase one (PP1) binding motif, with findings presented here confirming Arabidopsis PP1 phosphatases dock at this site. Intriguingly, only D‐group MPKs among all identified Arabidopsis protein kinases possess this PP1 recruiting motif. Using multiple RLPH2‐deficient plant lines, we demonstrate that RLPH2 represses seed dormancy release. Overall, this work highlights the power of phospho‐proteomics in identifying substrates of this novel plant tyrosine phosphatase while also revealing new complexities in the interactions between MPK activation loops and multiple phospho‐mediated cell signaling events.

Mechanical contributions are crucial regulators of diverse biological processes, yet their in vivo measurement remains challenging due to limitations of current techniques that can be destructive or require complex dedicated setups. This study introduces a novel method to synthesize biocompatible, self-functionalizing stress sensors based on inverted emulsions that can be used to probe stresses inside tissues but can also locally perturb the biological environment through specific binder presentation or drug delivery. We engineered an optimal design for these inverted emulsions, focusing on finding the balance between the two contradictory constraints: achieving low surface tension for deformability while maintaining emulsion instability for efficient self-functionalization and drug release. Proof-of-concept experiments in both agarose gels and complex biological systems, including brain organoids and zebrafish embryos, confirm the droplets ability to deform in response to mechanical stress applied within the tissue, to self-functionalize and to release encapsulated molecules locally. These versatile sensors offer a method for noninvasive stress measurements and targeted chemical delivery within living biological tissues, giving the potential to overcome current technical barriers in biophysical studies.Graphical abstractLeft 3 panels: Inverted emulsion droplets self-functionalize over time once injected in a biological medium. Right panel: After self-functionalization, the deformability of the droplets allows for the measurment of local stresses.