Manning Research Group

And also, what are all those oriented cell divisions doing to the tissue mechanics? stay tuned...

Dynamic regulation of tissue fluidity controls skin repair during wound healing During skin wound repair, the basal cell layer transitions from a solid-like homeostatic state to a fluid-like state that allows tissue remodeling during repair and then progressively returns to a sol...

Previous work from the Sprinzak and Campas/Simons/Blanpain labs suggest some interesting possible paths forward… www.cell.com/cell/fulltex... , www.cell.com/developmenta...

Future work: A key remaining open question on the physics side is precisely how this tissue-stiffness-dependent Notch activation is triggered – how do only a subset of cells (exactly the right number, perhaps not too close together) decide to commit?

Notch activity itself is gated by tissue stiffness and basal layer density/cell shape. This generates an elegant self-organizing feedback loop where delamination is directly link to the abundance and packing of basal layer stem cells, explaining the robustness of epithelial self-renewal.

The basement membrane and the basal layer of the tissue are substantially stiffer and less fluid-like at E15.5 and E16.5 compared to E14.5.

Cell state commitment in the basal layer activates Notch signaling. At E15.5 and E16.5 a population of Notch positive cells emerges that share characteristics of both basal and suprabasal cells, and also exhibit cell shapes and protein localization patterns consistent with cells that delaminate.

Next, we wonder how cells decide to commit to delamination at these later stages, so as to have precisely the right number of cells moving up to keep the basal layer in homeostasis (not over- nor under-populated).

At E14.5, only small changes to a cell’s mechanics (x-axis) are needed to get a cell to robustly delaminate (fraction of delaminating cells, y-axis -> 1). At E15.5 and E16.5, a very large change to cell mechanics is required to get a cell to delaminate.

We can use an Arrhenius approximation to extract the magnitude of the mechanical barrier to delamination from the rates of cell delamination. We find a large mechanical barrier emerges at E15.5 (and the barrier is small before that).

These changes -- predicted by fitting the model to experimental cell and tissue geometries -- are corroborated by observations of protein expression levels and localization.

At later stages (E15.5), the interaction with the basement membrane becomes wetting (negative sigma_b), and the heterotypic apical tension and tissue stiffness both increase, with further tissue stiffening even later at (E16.5).

The results are that at earlier stages (E14.5) the basal layer is soft (small delta s) with small heterotypic tension at the apical side (small sigma_a) and a positive, repulsive interaction with the basement membrane (sigma_b).

We used another set of data collapses to predict how each observable depends on model parameters, allowing us to use an overconstrained solver to determine the vertex model parameter that best match our experimental observations!

Three vertex model parameters control those observables – the cell stiffness parameterized in terms of a cell shape (delta s), a wetting tension with the basement membrane (sigma_b), and a heterotypic interfacial tension at the apical side of basal cells interacting with suprabasal cells (sigma_a).

In both simulations and experiments, we can measure 4 quantities – apical angle of basal cells, orientation of later interfaces with respect to the basement membrane, overall roughness of the basal-suprabasal interface, and height of basal cells.

To quantify how the magnitude of the barrier changes across developmental stages, we developed a method to match 3D vertex model parameters to cell- and tissue scale observables.

A vertex model simulation data collapse demonstrates that the rate at which cells are able to move upwards depends on a precise combination of the apical and basal tensions of the committed cell, as well as on the stiffness of surrounding cells.

We use a stratified 3D vertex model to demonstrate that the barrier prevents cells from freely moving across these compartments, unless a committed cell changes its mechanical properties.

At later stages perpendicular divisions are suppressed, and cells must commit to delamination and change their mechanical properties dramatically in order to move upward from the basal layer.

We demonstrate that there is a switch in multilayering strategy across development. At earlier stages, the mechanical barrier is quite small, so cells can easily divide perpendicularly to the basement membrane to populate upper layers.

Here, we study the developing stratified mouse epidermis to show that the physical separation of basal stem cells from suprabasal differentiating cells is driven by a mechanical boundary that forms between the layers during development.

Such feedbacks are becoming better understood in the small intestine, where stem cells reside in a “closed niche” defined by the crypt, but the stratified epidermis is an “open niche” that lack obvious morphological and geometric cues and even distinct molecular markers of cell states.

The mechanism by which these key tissues are generated and maintained has remained a key unresolved question, which is challenging because it involves feedbacks between cell mechanics, shape, and cell fate.

Multilayered self-renewing epithelia are vertebrate-specific tissues that function as life-essential barriers, controlling host–environment interaction and acting as disease entry points. cshperspectives.cshlp.org/content/10/1...

We’ll focus here on the key results of the paper from a physics of living systems perspective, and let our collaborators highlight some of the cell biology aspects.

Excited to highlight a new preprint about mechanical contributions to tissue homeostasis, from the Manning group in collaboration with the amazing Carien Niessen and Sara Wickstrom @sarawickstrom.bsky.social labs, spearheaded by Dr. Somiealo Azote: www.biorxiv.org/content/10.6...

And also, what are all those oriented cell divisions doing to the tissue mechanics? stay tuned...