Alfredo Sciortino

Congrats

Somebody doing a scientific présentation

Dress like your data like @timonnk.bsky.social does!

Synthetic cells get into shape - Nature Physics Shape changes in biological cells are driven by an active network of biopolymers. Now, similar deformations are observed in synthetic cell membranes.

Thanks to @agudocanalejo.bsky.social and @raovutukuri.bsky.social [amongst the first ones to observe large fluctuations in GUVs!] for today's News and Views about our recent paper on active vesicle deformations - and I agree with the conclusion, it's just a beginning..! doi.org/10.1038/s415...

Grande Gianni!

The Schaeffer magnum opus is out. 🔥

As always with @lauraal.bsky.social , the pleasrue is all mine ☺️ - thanks @crpp-bordeaux.bsky.social for the nice hospitality

Registration has started for the conference "Emerging Trends in the Physics of the Cell" in memoriam of Erich Sackmann at TU Munich from October 15-18 2025 www.cpa.tum.de/cpa/conferen...

Interesting read. Some problems are just weirder than you'd say.

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So, the DOGE kids intend to rewrite the social-security administration's COBOL code-base!

and they want to do it ...

... in *a few months*

I did a huge dive into COBOL a few years ago (www.wealthsimple.com/en-ca/magazi...) ...

... so let me explain why DOGE is *way* over its skis here

1/9

And Petia* 😅

I am very happy to share that my work on active deformations of lipid vesicles is finally out in Nature Physics. A nicer thread+movies coming soon, in the meantime:
www.nature.com/articles/s41...

Thx to Andreas, Hammad, Dmitry, Gerhard @laynefrechette.bsky.social and everybody else who contributed!

We are organizing a conference for young researchers at the intersection between physics & biology: www.embl.org/about/info/c... @embl.org @events.embl.org @intcha.bsky.social
Please consider applying/registering -- the deadline is already in one week!

A tweet by Elon Musk.

81% of Elon Musk thinks Elon Musk is a genius.

Graaaziee

Thanks!!

You know the pain 🥰 gracias

💘

So.. thanks for reading! I hope you liked it - and check out the preprint. Also thanks to @manuelthery.bsky.social and @lblanchoin.bsky.social , to Magali in particular, and to all coauthors (I think only @alexandra-colin.bsky.social is here..)! www.biorxiv.org/content/10.1...

Scheme of the transport process inside microwells.

So yes: filaments transport in 3D allows to separate a contractile flux at the bottom of the well with an extensile flux pushing filaments back to the periphery through the network's 3D architecture.

If the DSS is through filament transport in 3D then severing those bundles in the middle of the well should stop it. So we performed laser ablation and *zap* the bundles are gone and the DSS contracts and dies out.

Well apparently yes! The network uses its 3D architecture to "suck" filaments at the center and "inject" them back at the periphery - again, we show this with tracking filaments in 3D. But it's barely visible in the data, so we developed a killer experiment ;-) go to the next block to see it..

Well, if it is not nucleation and it is not transport in 2D, we might as well take a look at the network architecture in 3D! Using confocal we observe this weird tent-like structure - is it possible that filaments are transported through it?

Graph of actin filaments' speed.

What we find is that transport on the wells surface is coherent with actomyosin sliding combined with some "gliding" due to motors sticking to the membrane. But the net flux is still contractile, so what is pushing filaments back to the periphery...???

It's not actin turnover, the classical answer: this DSS works in the absence of actin nucleators or in the presence of phalloidin, i.e. with stabilized filaments. No depolymerization is present. So it has to be transport of the filaments. We combine a bunch of techniques to observe it, like speckle.

... and we got this: continuous actin contraction for hours and hours without collapse to the center. We also show how the flow and the actin architecture are organized in space in a regular way.
The question is... what is sustaining this dynamic state? What "compensates" for this contractile flow?

Schematics of a lipid coated microwell.

So we took some precautions: we isolated the system inside lipid coated microwells to provide a solid geometrical boundary [some more details on why exactly in the paper of course], we lowered the actin:myosin ratio in the hope that lowering network entanglement might help, we crossed our fingers...

Problem is, traditionally reconstituted actomyosin networks just to a big whooooosh and quickly contract to a single point.

Schematics of "in vitro reconstitution", i.e. the use of purified proteins to build cellular architectures in a lab environment.

Of course understanding DSSs in cells is hard: different architectures (lamellipodia, stress fibers, cortex) interact and share monomers and dissecting all the "fluxes" present is different. You can use cell extracts, which are cool but still complex. Or... use the power of in vitro reconstitution!

This is the actin cytoskeleton in a cell (by A. Schaeffer). Actin structures arecontinuously renewed, contracted and dissassembled in cells, to create architectures that have always the same "shape" but are microscopically fueled by fluxes of new material. We call it a dynamic steady state (DSS).

New preprint out 🔥🔥 on my postdoc work with @manuelthery.bsky.social and @lblanchoin.bsky.social about how we can create sustained dynamic steady states of actin network inside microscopic wells that contract "forever" without collapsing! A thread 🧵
www.biorxiv.org/content/10.1...