John Gurdon will be deeply missed: a sharp mind, a warm and witty sense of humour, and a visionary who shaped our understanding of developmental biology. I admired his intelligence, envied his prominent hair🙂. Left photo, in archives of Nobel, taken by John Overton, photographer and our lab manager.

This is the second simulation, with contractility and stiffness increasing over time (the latter derived from what we learnt using Brillouin microscopy):

Finally, we developed a physical toy model of mesoderm folding to test if the dynamic, localised increase in stiffness facilitates folding the mesoderm? The answer is YES!. See the simulations ⤵️: first movie: ✅contractility ❌stiffness; second movie: ✅contractility ✅ stiffness.

How do microtubules make mesoderm cells -transiently- stiffer? Using live imaging & 3D-SIM, we found microtubules reorganise within the cell's sub-apical compartment, -where we measure the stiffening- by becoming increasingly aligned with each other during mesoderm folding:

We wanted to understand what makes the mesoderm transiently stiff during its folding & invagination. We did not see a correlation between actomyosin and the increase in stiffness. But surprise!: We depolymerised microtubules using Colcemid (right panel) and mesoderm cells remained in a softer state😱

On the contrary, the ectodermal cells located on the dorsal side of the embryo become softer! In sum, the embryo undergoes two diverging mechanical transitions: mesoderm: stiffening followed by softening; ectoderm: softening. See ⤵️ the softening of dorsal cells when they flatten and stretch:

Gastrulation starts when the mesoderm (bottom in ⬆️), folds and invaginates, and next, undergoes EMT. Here, we measured fast and biphasic mechanical dynamics: during mesoderm invagination, cells stiffen (Brillouin shift map -bottom panel-, transient yellow); during EMT, mesoderm cells soften.

Using Brillouin microscopy, we measured changes in stiffness within the whole-cell of an intact organism.
We focused on the most important event in our life: gastrulation, which in Drosophila is really fast (~30'):

🥁 New article 📢: #Mechanobiology of #development during #Drosophila #gastrulation using #Brillouin microscopy, now in @natcomms.nature.com : rdcu.be/ev6ZX
Collab. w/ @Prevedel_Lab @embl.org , Maria Leptin @marialep.bsky.social, @abhisha-thayambath.bsky.social, Julio Belmonte @ncstate.bsky.social

📣 Wanna hear our story about the complex mechanical dynamics that cell populations undergo during the most important morphogenetic event? -Of course I am talking about gastrulation 🙂🤘. Join us this Wed at 10:00 CET, details -> @vgzt2021.bsky.social @embl.org @prevedel-lab.bsky.social