Biology subjects

Bernat-Fabre, S.

Publications and source records attributed to Bernat-Fabre, S..

5 recordsLinked to original sources

bioRxiv2025

Robust pan-junctional reinforcement preserves the gut epithelial barrier under mechanical stress

Epithelia are specialized tissue barriers that safeguard the organisms internal milieu from the hostile external environment, a function critically dependent on intercellular junctions. In the colon, this barrier is repeatedly challenged by mechanical distension from faeces and it is unknown whether and how the colon adapts to such stress, which could otherwise compromise barrier integrity. Here, we show that faeces-mediated mechanical distension triggers coordinated remodelling at cell- and tissue-scale, suggestive of mechanoadaptation. This response includes recruitment of junctional proteins at all three types of adhesive cell-cell junctions (tight junctions, adherens junctions and desmosomes). We identified two modes of recruitment: stable responders (ZO-1, E-cad, plakoglobin) with sustained junctional enrichment, and adaptive responders (desmoplakin, keratin 8) with progressive accumulation during distension. Distension was also accompanied by perijunctional recruitment and activation of non-muscle myosin II (NMMII). Through genetic, pharmacological, and mechanical perturbations, we demonstrated that NMMII activation is an early and critical step for mechanoadaptation. This process requires extracellular calcium influx, and Piezo1 activation is sufficient to trigger NMMII activation and junctional recruitment. Loss of NMMII function abrogated the junctional response to distension across all three junctional complexes, including desmosomes, resulting in disorganised junctions and barrier breach. Together, our findings uncover a robust physiological mechano-adaptive response of the adult colonic epithelium to an extrinsic mechanical stress, whereby coordinated reinforcement of all junctional complexes, controlled by myosin II and mechanosensitive calcium influx, plays an essential role in preserving intestinal barrier integrity.

cell biology↗

bioRxiv2025

The Mediator complex subunit Med19 extends healthy lifespan in Drosophila by preventing cellular and organismal frailty

Aging involves a progressive decline in physiological functions, often marked by the onset of a "frailty point" just before survival rates decrease rapidly. Here, we investigate how the Mediator subunit Med19 modulates this transition in Drosophila. We find that upregulating Med19 extends the median lifespan by nearly 90% and postpones the onset of accelerated mortality, suggesting that Med19 helps preserve the resilience phase of aging. In contrast, Med19 downregulation sharply reduces both median and maximum lifespan, advancing the frailty threshold. We show that Med19 knockdown increases fly vulnerability to environmental insults such as oxidative and genotoxic challenges whereas Med19 upregulation helps them resist these stresses, underscoring Med19s protective role in maintaining genomic integrity. We link these phenotypes to altered stress-response pathways at the cellular level: Med19-depleted cells show a compensatory upregulation of genes involved in iron-sulfur cluster biogenesis, glutathione metabolism, and DNA damage repair. At the cellular level, Med19 depletion triggers a "loser" phenotype in cell competition assays, activating the JNK pathway and undergoing apoptosis, highlighting a form of "cellular frailty" that parallels organismal frailty. Finally, we found that the Med19 protein level naturally decreases with age and showed that restoring Med19 expression in aged flies increases fitness and delays the onset of frailty even in older, "frail" individuals, underscoring its significance as an aging regulator. Altogether, our findings establish Med19 as a crucial mediator of lifespan and stress resilience, suggesting it acts as a rheostat that modulates the transition from healthy aging to frailty in Drosophila. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=180 HEIGHT=200 SRC="FIGDIR/small/659864v1_ufig1.gif" ALT="Figure 1"> View larger version (54K): org.highwire.dtl.DTLVardef@1a5e398org.highwire.dtl.DTLVardef@14658org.highwire.dtl.DTLVardef@1b14089org.highwire.dtl.DTLVardef@41060_HPS_FORMAT_FIGEXP M_FIG C_FIG Highlights- At the organismal level, Med19 upregulation extends Drosophila lifespan by 90%, delays the onset of frailty and enhances oxidative and DNA damage stress resistance, while its depletion has the opposite effect. - Med19 depletion alters the expression of stress response genes and induces a loser-cell phenotype in cell competition assays revealing its crucial function in controlling cellular fitness. - Med19 protein levels naturally decline with age, and its restoration in aged flies improves both healthspan and lifespan.

cell biology↗

bioRxiv2025

Goblet cells mechanically breach the epithelial barrier in gut homeostasis

The intestinal epithelium has to maintain a tight barrier against the harsh luminal environment. Absorptive enterocytes have a polygonal and columnar shape, while mucus-producing goblet cells exhibit a round apical cell shape and a bulky body, raising the question of how epithelial integrity is maintained around these cells. Here, we show that goblet cells induce tight junction fractures between neighboring enterocytes under homeostatic conditions in vivo, which are exacerbated during goblet cell hypertrophy, increasing gut permeability. We demonstrate that these fractures arise from a two-component mechanical interaction: goblet cells push and deform adjacent enterocytes, which rupture depending on tissue rheology controlled by myosin II. These findings reveal that the mechanical interplay between goblet cells and neighboring enterocytes is critical for maintaining intestinal epithelial barrier integrity.

cell biology↗

bioRxiv2022

Inducible degradation of the Drosophila Mediator subunit Med19 reveals its role in regulating developmental but not constitutively-expressed genes

The multi-subunit Mediator complex plays a critical role in gene expression by bridging enhancer-bound transcription factors and the RNA polymerase II machinery. Although experimental case studies suggest differential roles of Mediator subunits, a comprehensive view of the specific set of genes regulated by individual subunits in a developing tissue is still missing. Here we address this fundamental question by focusing on the Med19 subunit and using the Drosophila wing imaginal disc as a developmental model. By coupling auxin- inducible degradation of endogenous Med19 in vivo with RNA-seq, we got access to the early consequences of Med19 elimination on gene expression. Differential gene expression analysis reveals that Med19 is not globally required for mRNA transcription but specifically regulates positively or negatively less than a quarter of the expressed genes. By crossing our transcriptomic data with those of Drosophila gene expression profile database, we found that Med19-dependent genes are highly enriched with spatially-regulated genes while the expression of most constitutively expressed genes is not affected upon Med19 loss. Whereas globally downregulation does not exceed upregulation, we identified a functional class of genes encoding spatially-regulated transcription factors, and more generally developmental regulators, responding unidirectionally to Med19 loss with an expression collapse. Moreover, we show in vivo that the Notch-responsive wingless and the E(spl)-C genes require Med19 for their expression. Combined with experimental evidences suggesting that Med19 could function as a direct transcriptional effector of Notch signaling, our data support a model in which Med19 plays a critical role in the transcriptional activation of developmental genes in response to cell signaling pathways. Author summaryThe Mediator is a large evolutionarily conserved multisubunit complex that plays essential functions in gene expression by relaying cues emanating from enhancer-bound transcription factors to the RNA polymerase II machinery. The transcriptional landscapes regulated by each Mediator subunit, especially in vivo in the context of developmental processes, remains poorly characterized. We therefore sought to provide a comprehensive view of the genes directly regulated by Med19, an archetypal Mediator subunit, in the context of the development of the Drosophila wing. Our work has important methodological implications as to carry out our analysis in the best experimental conditions, we generated mutant flies in which we could trigger fast degradation of the Med19 subunit on demand in the tissues of the living animal. We found that only a small part of the genes expressed in the developing wing are controlled by Med19 showing that this Mediator component exercises specific functions. Another major finding is the strong involvement of Med19 in the regulation of the expression of the genes involved in developmental processes supporting the idea that Med19 is a Mediator component dedicated to highly regulated mode of gene expression. The most unanticipated discovery of our study is the fact that Med19 does not appear to play a role in the expression of the genes that are constitutively transcribed, among which the housekeeping genes. This raises the notion that in the context of simple --non-regulated-- mode of expression, part of the Mediator functionalities, among which Med19, otherwise dedicated to highly regulated type of transcription, may become dispensable.

developmental biology↗

bioRxiv2020

Mediator complex subunit Med19 binds directly GATA DNA-binding zinc finger and functions with Med1 in GATA-driven gene regulation in vivo

The evolutionarily-conserved multiprotein Mediator complex (MED) serves as an interface between DNA-bound transcription factors (TFs) and the RNA Polymerase II machinery. It has been proposed that each TF interacts with a dedicated MED subunit to induce specific transcriptional responses. However, binary MED subunit - TF partnerships are probably oversimplified models. Using Drosophila TFs of the GATA family - Pannier (Pnr) and Serpent (Srp) - as a model, we have previously established GATA cofactor evolutionarily-conserved function for the Med1 Mediator subunit. Here, we show that another subunit, Med19, is required for GATA-dependent gene expression and interacts physically with Pnr and Srp in cellulo, in vivo and in vitro through their conserved C-zinc finger (ZF), indicating general GATA co-activator functions. Interestingly, Med19 is critical for the regulation of all tested GATA target genes which is not the case for Med1, suggesting differential use of MED subunits by GATAs depending on the target gene. Lastly, despite their presumed distant position within the MED middle module, both subunits interact physically. In conclusion, our data shed new light first on the MED complex, engaging several subunits to mediate TF-driven transcriptional responses and second, on GATA TFs, showing that ZF DNA-binding domain also serves for transactivation.

developmental biology↗