Time flies – Pulling it off at last!
The development of an organism from a fertilized egg encompasses intricate rearrangements of cells and tissues. Think of a paper boat! Starting from a plain sheet of paper, by repeated folding a complex 3D shape emerges which can function in ways the original piece of paper could not. Something very similar is taking place in a developing embryo. Sheets of cells, which we call tissues, have to fold, bend, seal gaps, and perform complex spatial movements in order for the organism to acquire its final shape and function. Now, when folding a sheet of paper you need to exert the right forces with your hands. That alone, however, is not enough to understand the whole process. Cause what if the sheet was actually not made from paper but from steel instead. In that case, the same manipulation with your hands would not result in a paper boat, but only in frustration and sore fingers. In other words, if you want to understand something like the folding of a paper boat, you need to understand the forces and the materials which are part of the process. The same is true for embryonic development. In order to really understand how a fly, or snail, or a human baby can form from a single dividing cell, we need to understand not only what forces act within the embryo, but also what the physical characteristics are of the “stuff” that the embryo is consisting off.
That is exactly the topic of a recently published paper of mine, which contains work that still originates from the time when I was a postdoc in Spain. In the course of this collaborative project, we developed a novel method for measuring the physical material properties of tissues in living fruit fly embryos. To achieve this goal, we injected tiny magnetic beads, smaller than individual cells, into the developing embryo and pulled on them with an electromagnet. Using quantitative image analysis and biophysical modelling, from these experiments we could e.g. determine whether a given tissue was soft or stiff. In particular, we could show that the embryo has the ability to rapidly modulate its material properties, i.e. change from stiff to soft in a matter of minutes! Why could this be of importance? Think of a piece of wax which you intend to mold into a certain form, let’s say a fruit fly. To achieve this goal you squeeze it with your fingers. But since the wax is hard, nothing is happening. However, when you heat the wax you make it go from stiff to soft. And then, while exerting the same force with your fingers, the wax will begin to start changing its shape. Our work provides evidence, that a similar mechanism (which proceeds without heating) is important for embryonic development to successfully proceed from a fertilized egg cell to final organism.
If you are interested, please, check out the original publication which you can download for free here:
A. D’Angelo*, K. Dierkes*, C. Carolis, G. Salbreux, J. Solon, In Vivo Force Application Reveals a Fast Tissue Softening and External Friction Increase during Early Embryogenesis, Current Biology, 29 (9), 2019. (* shared first authors)