Biology subjects

Ruemmele, F.

Publications and source records attributed to Ruemmele, F..

5 recordsLinked to original sources

bioRxiv2026

EpCAM sustains crypt mechanics and prevents aberrant remodeling

Crypt morphogenesis is a fundamental process that drives intestinal growth and maintains its homeostasis. Although intestinal tissue mechanics is recognized as pivotal for early crypt initiation and budding, the molecular mechanisms that couple epithelial forces to mature crypt behavior remain largely unexplored. In particular, while Paneth cells have been proposed to be implicated in the mechanical control of crypt remodeling and fission, the underlying pathways have remained elusive. Here, we identified EpCAM (Epithelial Cell Adhesion Molecule) as a key regulator of epithelial contractility and crypt morphogenesis. EpCAM was preferentially enriched at lateral interfaces of Paneth cells in vivo and in organoid models, where it maintained cortical tension and contractile organization. Loss of EpCAM disrupted crypt cell cortical myosin II-A localization, leading to aberrant Paneth cell apical contractility, enlarged apical surfaces, distorted pyramidal morphology, and altered aspect ratios. Consequently, Paneth cells lose their tight clustering in crypt base, their spatial distribution along the crypt axis becomes irregular, and the collective architecture of the crypt epithelium was compromised. At the tissue level, EpCAM deficiency profoundly perturbed crypt fission, increasing fission frequency while favoring asymmetric outcome both in EPCAM-mutated Congenital Tufting Enteropathy (CTE) patients. Live imaging of EpCAM-knockout mouse organoids confirmed a failure in the spatial control of crypt bifurcation. Collectively, our findings revealed that EpCAM is not required to initiate fission, but is essential to coordinate the mechanical forces and ensure correct division of the crypt. We showed that EpCAM-dependent biomechanical integrity of Paneth cells generates a stabilizing force field at the crypt base, orchestrating coordinated tissue remodeling. Disruption of this program led to unbalanced force transmission, distorted crypt geometry, and aberrant fission outcomes, revealing a critical link between epithelial mechanics and intestinal morphogenesis.

developmental biology↗

bioRxiv2024

A multicellular actin star network underpins epithelial organization and connectivity

Epithelial tissues serve as physical barriers against various external pressures yet remarkably maintain structural stability. Various cellular apparatus including bicellular junction and actomyosin network contribute to the epithelial integrity, packing and remodelling. Although their role in morphogenetic and mechanical processes have been extensively studied during embryogenesis and disease development, their synergistic effects in maintaining tissue organization and connection remain poorly understood. In this study, we discovered a tissue-scale actomyosin network connected through bicellular junctions and manifested in the villi of adult murine intestinal tissue. Later we reproduced such supracellular structure in the differentiated compartment of ex vivo intestinal epithelium model. The self-organized actomyosin networks comprised individual actin nodes in each hexagonal cell at the epithelial base with six radial actin branches, presenting an actin star unit. The repeated units were connected through the bicellular junctions, forming a large, multicellular array covering the differentiated domains. Functionally, actin stars contribute to epithelial morphological stability by maintaining cell hexagonality and packing, thereby preserving the solid-like order of the epithelium. Laser ablation experiments validate a modified vertex theoretical model that connects the emergence of such solid-like order to the onset of tension along the actin star branches. Actin stars also acted as locks at the basal side minimizing protrusive activity in the epithelial layer, hindering cell migration and disorganization of the epithelial tissue. Altogether, the supracellular actin star network constitutes a basal biomechanical apparatus coordinating epithelial tissue stability and organization.

cell biology↗

bioRxiv2022

V0-ATPase downregulation induces MVID-like brush border defects independently of apical trafficking in the mammalian intestine

SummaryIntestinal microvillus atrophy is a major cause of enteropathies such as idiopathic or congenital diarrhea that are often associated with severe morbidity. It can be caused by genetic disorders, inflammatory diseases, toxins or pathogens. In particular, Microvillus inclusion disease (MVID) is characterized by a chronic intractable diarrhea and a severe microvillus atrophy. It is triggered by mutations in MYO5B, STX3, MUNC18.2 or UNC45A which alter epithelial polarity by affecting apical trafficking in intestinal epithelial cells. Furthermore, we recently established that the depletion of the V0 sector of the V-ATPase complex induces an MVID-like phenotype in C. elegans. In this study we investigated the function of the V0-ATPase complex in mouse intestinal organoids. We found that its depletion also triggers a very severe microvillus atrophy in this model. Furthermore, we established that the polarity of intestinal cells is affected in a patient carrying mutations in TCIRG1 which encodes a V0-ATPase subunit. However, V0- ATPase depletion does not recapitulate other MVID-specific phenotypes such as subapical vesicle accumulation and Rab11+ endosomes mislocalization. Finally, we found that the apical localization of the V0-ATPase is disrupted in MVID patients. Altogether these results suggest a role for the V0-ATPase in microvillus atrophy which might be independent from apical trafficking.

cell biology↗

bioRxiv2020

Single cell analysis of FOXP3 deficiencies in humans and mice unmasks intrinsic and extrinsic CD4+ T cell perturbations

ABSTRACTFOXP3 deficiency in humans with IPEX syndrome and mice results in fatal systemic autoimmunity by altering regulatory T cell (Treg) physiology, but actual cellular and molecular mechanisms of disease are unclear, part because Treg surface markers may be unreliable in disease states. We used deep profiling by flow cytometry, population and single-cell RNAseq to analyze Tregs and conventional (Tconv) CD4+ T lymphocytes in cohorts of IPEX patients with a range of genetic lesions, and in Foxp3-deficient mice. In all patients and mice, heterogeneous Treg-like cells with an active FOXP3 locus were observed, some differing very little from normal Tregs, others more distant. Tconv showed no widespread activation or Th bias. The dominant mark was a monomorphic signature equally affecting all CD4+ T cells, unexpectedly dampening tumor-Treg and cytokine-signaling modules. In mixed bone marrow chimeras, WT Tregs exerted dominant suppression, normalizing the states of mutant Treg and Tconv, extinguishing the disease signature, and revealing a small gene cluster truly regulated, cell-intrinsically, by FOXP3. These results suggest a two-step pathogenesis model, with therapeutic implications: limited downregulation of a few core Treg genes de-represses a systemic mediator(s), which imprints the disease signature on all T cells, and further dampens Treg function.Competing Interest StatementThe authors have declared no competing interest.View Full Text

immunology↗

bioRxiv2019

Network Analysis Of Inflammatory Bowel Disease Reveals PTPN2 As New Monogenic Cause Of Intestinal Inflammation

BACKGROUND & AIMSGenome-wide association studies (GWAS) have uncovered multiple loci associated with inflammatory bowel disease (IBD), yet delineating functional consequences is complex. We used a network-based approach to uncover traits common to monogenic and polygenic forms of IBD in order to reconstruct disease relevant pathways and prioritize causal genes.\n\nMETHODSWe have used an iterative random walk with restart to explore network neighborhood around the core monogenic IBD cluster and disease-module cohesion to identify functionally relevant GWAS genes. Whole exome sequencing was used to screen a cohort of monogenic IBD for germline mutations in top GWAS genes. One mutation was identified and validated by a combination of biochemical approaches.\n\nRESULTSMonogenic IBD genes clustered siginificantly on the molecular networks and had central roles in network topology. Iterative random walk from these genes allowed to rank the GWAS genes, among which 14 had high disease-module cohesion and were selected as putative causal genes. As a proof of concept, a germline loss of function mutation was identified in PTPN2, one of the top candidates, as a novel genetic etiology of early-onset intestinal autoimmunity. The mutation abolished the catalytic activity of the enzyme, resulting in haploinsufficiency and hyper-activation of the JAK/STAT pathway in lymphocytes.\n\nCONCLUSIONSOur network-based approach bridges the gap between large-scale network medicine prediction and single-gene defects and underscores the crucial need of fine tuning the JAK/STAT pathway to preserve intestinal immune homeostasis. Our data provide genetic-based rationale for using drugs targeting the JAK/STAT pathway in IBD.

immunology↗