Denis Krndija

Amazing work by Vishnu & the MechanoGut team! 💩⚙️🛠️ Huge thanks to @cbitoulouse.bsky.social imaging & animal facilities, our dear colleagues and collaborators, and funders @cnrs.fr ATIP-Avenir, ED-BSB, @frm-officiel.bsky.social
#Mechanobiology #GutBarrier #EpithelialBiology #CellAdhesion

Pathologically, when this adaptive capacity is exceeded – as in IBD, fibrotic strictures, obstruction, or toxic megacolon – barrier failure and inflammation may ensue. Understanding these mechanisms could inform new strategies to restore epithelial integrity in disease.

Our findings resonate with work from A. Yap, A. Miller, K. Green, C. Niessen, G. Charras and others on how junctional tension and cytoskeletal coupling sustain epithelial resilience. We reveal that such mechano-adaptive coordination also operates in vivo, in an adult organ under mechanical stress.

Also, this work sheds more light on the unexpected dynamics of desmosomes and intermediate filaments – long seen as static anchors, now increasingly recognised as mechano-responsive players in epithelial resilience!

🧠 Take-home:
The gut epithelium isn’t a passive barrier – it’s relentlessly adaptive.
Extrinsic forces from faeces trigger a rapid, coordinated reinforcement of all junctional complexes, preserving barrier function and homeostasis under continuous stress 💩💪 (11/11)

Top: Schematic of the proposed mechanoadaptation pathway in colonic epithelium, illustrating how failed junctional recruitment may lead to barrier breach. Left: Representative images of colonic epithelium stained for F-actin (cyan) and acc. E-cad (grey) in NMMIIA-KO mice from ND and faeces-D regions. Red arrows indicate breached junctions. Maximum Z-projection (1-3 µm range). Scale bar: 5 µm. Right: Bar plots showing percentage of accessible E-cad (acc. E-cad)-positive junctions in control and NMMIIA-KO mice from ND and faeces-D regions, or in ND and D explants after indicated treatments.

Using a luminal-accessibility assay for E-cadherin, we found that depleting NMIIA in vivo or inhibiting myosin II / Ca²⁺ influx ex vivo led to barrier breaches under mechanical stress.
The junctional response is therefore essential for maintaining epithelial integrity (10/11)

Left: Representative images showing colonic explants, stained for ZO-1 (magenta) and pMLC (S19) (cyan) in ND after Yoda1 or vehicle control (DMSO) treatment for 15 min. Maximum Z-projection (1-3 µm range). Scale bar: 5 µm. Top-right: Box plot showing junctional pMLC intensity in Yoda1-treated and vehicle control (DMSO)-treated ND explants. Bottom-right: Comparative box plot showing junctional ZO-1 intensity fold change in distended explants after pre-treatment with mechanosensitive ion channel inhibitors or Piezo1 activator. Dotted line represents the normalised average for ND.

Conversely, activating Piezo1 was enough to trigger NMII activation and junctional recruitment.
👉 Mechanosensitive Ca²⁺ influx is both necessary and sufficient for junctional reinforcement under force ⚡️(9/11)

Left: Representative image showing colonic explants, stained for ZO-1 in ND and D after Gd3+ or vehicle control (water) treatment as indicated in (B). Maximum Z-projection (1-3 µm range). Scale bar: 5 µm). Right: Box plot showing junctional pMLC intensity in Gd3+ treated and vehicle control (water)-treated ND and D explants.

💡 What activates myosin II under mechanical stress?
Blocking mechanosensitive ion channels (with Gd³⁺) or chelating extracellular Ca²⁺ (with BAPTA) prevented NMII activation and junctional reinforcement – stopping the mechano-adaptive response in its tracks (8/11)

Left: Representative image of colonic epithelium stained for ZO-1 in control and NMMIIA-KO mice from ND and faeces-D regions. Maximum Z-projection (1-3 µm range). Scale bar: 5 µm. Top-right: Comparative box plot showing fold change in junctional protein levels (tight junctions (TJ), adherens junctions (AJ) and desmosomes (DS)) in faeces-D regions of controls and NMMIIA-KO mice. Dotted line represents the normalised average for ND. Bottom-right: Comparative box plot showing junctional ZO-1 intensity fold change in distended explants after pre-treatment with upstream myosin II inhibitors or Calyculin A. Dotted line represents the normalised average for ND.

Genetic deletion (Myh9-KO in vivo) or pharmacological inhibition of NMII ex vivo abolished junctional recruitment across all complexes.
👉 NMII acts as a central effector coordinating force sensing and junctional reinforcement.🔩 (7/11)

Left: Representative images, segmented and colour-coded based on apical cell area in ND and D regions after 5, 15 and 30 min of distension. Maximum Z-projections (1-3 µm range). Scale bar: 5 µm. Right: Line plot showing mean fold change in cell area and NMMIIA-GFP intensity after 5, 15 and 30 min of distension. Dotted line represents the normalised average for ND.

Junctional reinforcement coincided with recruitment of myosin IIA (NMIIA) to perijunctional belts and transient apical constriction – hallmarks of contractile activation.
Unexpectedly, myosin IIC, usually linked to microvilli, also relocalized to junctions under force ⚙️ (6/11)

Top: Scheme showing experimental approach for catheter-mediated in vivo distension of the mouse colon. Bottom-left: Comparative line plot showing junctional intensity fold change for ZO-1, E-cad and PG after 5, 15 and 30 min of distension. Dotted line represents the normalised average for ND. Bottom-right: Comparative line plot showing junctional intensity fold change for DP and KRT8 after 5, 15 and 30 min of distension. Dotted line represents the normalised average for ND.

Using a controlled in vivo colonic distension system (with Nicolas Cenac, IRSD Toulouse), we uncovered two kinetic modes:
- Tight & adherens junctions → sustained reinforcement
- Desmosomes & keratin filaments → progressive accumulation over time (5/11)

Left: Scheme showing adhesive cell-cell junctions in colonic epithelium. Middle: Representative en face images of colonic epithelium, stained for tight junction (TJ) protein ZO-1, Adherens junction (AJ) protein E-cad, and desmosomal (DS) protein Desmoplakin (DP) and desmosome-associated intermediate filament (IF), K8 in both ND and D regions. Maximum Z-projections (1-3 µm range). Scale bar: 5 µm. Right: Representative transverse images of colonic epithelium, stained for K8 (cyan) and DP (magenta) in both ND and D regions. Maximum Z-projections (2-4 µm range). Scale bar: 5 µm

This mucosal remodelling comes with striking reinforcement of tight, adherens, and desmosomal junctions – a robust, pan-junctional mechano-adaptive response.
The adult gut epithelium actively adapts to physiological mechanical stress 💪 (4/11)

Representative images of thick section of mouse colonic tissue in transverse view, showing lumen, plateau regions (white brackets), muscle layers and crypts (outlined in yellow dashed lines), and stained for F-actin (magenta), DAPI (cyan) and laminin (grey) in both ND and D regions. The left panel is a tiled confocal reconstruction. Right panel: Representative transverse images of plateau regions in the colonic epithelium, stained for F-actin (magenta), DAPI (cyan) and laminin (grey) in both ND and D region. Basal side of the cell outlined as yellow dashed line. Maximum Z-projections (2-4 µm range). Scale bars: left panel, 500 µm; middle panel, 50 µm; right panel: 5 µm.

💩 Faeces matter – mechanically!
Most studies remove luminal contents before analysis – we didn’t.
Keeping them revealed that the colonic mucosa adapts to faecal distension through large-scale tissue unfolding and epithelial deformation (3/11)

Mechanical forces shape tissues throughout development and physiology – yet in vivo evidence for mechano-adaptation in adult organs remains scarce.
The colon must regularly accommodate voluminous faeces, but how it adapts to this load while maintaining barrier integrity was unknown (2/11)

Robust pan-junctional reinforcement preserves the gut epithelial barrier under mechanical stress Epithelia are specialized tissue barriers that safeguard the organism's internal milieu from the hostile external environment, a function critically dependent on intercellular junctions. In the colon,...

Ever wondered how adult organs preserve epithelial barrier integrity while continuously exposed to mechanical stress? We tackled this question in our new preprint – led by our brilliant PhD student Vishnu Krishnakumar! (1/11)
🔗 www.biorxiv.org/content/10.1...

Cell-type-specific nucleotide sharing through gap junctions impacts sensitivity to replication stress in Drosophila Boumard et al. demonstrate gap-junction-dependent tissue-scale nucleotide sharing, which impacts cellular sensitivity to perturbation of nucleotide homeostasis and replication stress. Drosophila wing ...

The PhD work of @bboumard.bsky.social officially out in print! Happy to share this issue with our downstairs colleagues in the BDD @frelab.bsky.social @robinjournot.bsky.social

www.cell.com/developmenta...

Can pressure gradients persist over long timescales in animal cells? We induced intracellular pressure gradients and examined the resulting flows in single cells. We reveal surprisingly long lasting pressure gradients.

More here: elifesciences.org/reviewed-pre...

Our paper is on the cover of @cp-devcell.bsky.social . Image: embryonic murine salivary-gland explants stained for fate determinants; p63 (cyan) and HES1 (yellow). Thanks to everyone involved.
doi.org/10.1016/j.de...

Latest from ours: www.cell.com/cell-reports...

This is two stories in one: a case study/cautionary tale on developing genetic tools in new organisms, and the first hint at a gene regulatory network for choanoflagellate multicellular development (which turn out to involve a Hippo/YAP/ECM loop!) A 🧵

Are you interested on how regenerating tissues transit between stages? Am sharing here our work showing that during #Xenopus tail regeneration, tissue stiffening activates a Piezo1-Yap1 mechanosensitive cascade to allow wounded epithelia to transit into regenerative states!

Three-Year Funded Postdoctoral Position to study organelle architecture in mammalian oocytes – Terret-Verlhac Lab, CIRB, Collège de France (Starting 2026).
For more information, please contact: marie-helene.verlhac@college-de-france.fr

🚨 New paper out in @pnas.org! 🚨

We show that self-generated gradients allow heterogeneous cell mixtures to co-migrate efficiently over long distances —while optimizing their physical interactions!

(See below for 🧵)

www.pnas.org/doi/10.1073/... 🧪

Synthetic materials accumulate damage with every mechanical challenge. Epithelial tissues are regularly loaded, yet healthy epithelia rarely rupture. Why?

We are @epmech.bsky.social and @baldaufsci.bsky.social and in this thread we introduce you to cyclic loading.

bsky.app/profile/epim...

Mechanical forces shape the developing brain 🧠💥 Compression from high cell density doesn’t just squeeze cells - it compromises mitotic fidelity! New preprint on how mechanics impact neural development from Veronique Marthiens & co-authors @institutcurie.bsky.social @cbitoulouse.bsky.social
🧠🔧👇

Well done Robin and @frelab.bsky.social on this beautiful story - it’s great to see it published!! Bravo 👏 🍾 🥳

🧵Just out !
We reveal how 4 branched epithelia—mammary, lacrimal, salivary & prostate—use a conserved YAP–Notch–p63 circuit to self-organize during development & regeneration.
Here’s the story👇
authors.elsevier.com/c/1lM285Sx5g...
Work done in @frelab.bsky.social at ‪
‪ @institutcurie.bsky.social

My first experience at a GRC- excellent talks & stimulating conversations. Thanks to everyone to who stopped by my poster- your feedback were incredibly valuable to me. And of course, infinite gratitude goes to @yap-lab.bsky.social, an exceptional mentor and support throughout my journey!

Woohoo!! Congrats @julianeg.bsky.social !!! 🍾 🥳

A highlight of our recent story!

Thanks for your insights, Marija! 🙌 🥰
We're excited to explore how mechanical forces shape physiological complexity between distinct epithelial cell types in vivo. And yes - tricellular junctions reinforce under compression, but often crack first… and kick off the further fracturing process! 💥