Okay, good. So good morning, everyone. I would like to give a hopefully brief seminar on

the topic, what properties or which properties of the exocellular matrix are important for

cell behavior in a three-dimensional environment. So I'm Ben Fabry from the Department of Physics.

I'm head of the biophysics group and I have been working for many years on the topic of

cancer cell migration and other cells that migrate in a three-dimensional environment.

And so we have already here the first problem. This should be a movie that doesn't move.

All right, then we do it without the movie. What you would see would be a cancer cell

that migrates through a three-dimensional collagen matrix and then divides. And what

we learned over the time is summarized here on the slide that for their normal function,

that most cells, in particular, most mesenchymal cells like fibroblasts, many cancer cells

and so on, they need to adhere and they need to spread for their normal behavior. They

need space to grow and to divide and space to move. Not all cells, of course, need to

move in order to behave normally, but in particular, single cells and cells that we have been interested

in over the past years. We wanted them to have an environment where they move in particular

when we are interested in questions like cancer cell migration. So our matrix that we use

for our three-dimensional studies is collagen. And I will talk a little bit more about this

collagen matrix, which cells really like because they can adhere, they can spread, they can

grow and invade. And the properties that collagen has that allows these cells to do these behaviors

is that collagen is suitably adhesive, it's suitably porous and degradable, and it's not

too stiff and not too soft. And by suitably adhesive, I also mean it's not too adhesive

and not too strongly, not too weakly adhesive. It just has the right degrees of porosity

and degradability. So these are obviously properties that matter. And that's, if you

wish, already the summary slide. So if you're getting bored, this is what I'm going to tell

you that the combination of adhesiveness, porosity and degradability and mechanical

properties, this is what determines how cells behave in 3D. Now, my group or I myself have

no experience previously in the behavior of neural cells. So what degree and what type

of adhesiveness they need, what type of porosity or size of porosity and stiffness range they

like, I don't know. But that's something that we as a consortium are planning to investigate

and find out. So I will start with some very basic and old studies that looked at this

behavior not in 3D, but in 2D, because many things that we can measure in 2D apply, of

course, also to the 3D, to the three-dimensional world. So on the left-hand side, you see a

copy from a famous textbook. So that's Albert's Molecular Biology of the Cell. And this depicts

how cells are thought to migrate on a two-dimensional flat substrate. So the cells essentially make

protrusions in the form of a lamellipodium. It starts then to adhere or make new adhesions,

generates the contractile forces that then cause the cell's rear end to detach from

the substrate to break the adhesions. And then the cycle repeats, this new filopodia

or lamellipodia extensions at the front and so on. So a study from the early 90s by the

laboratory of Doug Laufenberger looked at the importance of adhesion for this process.

And they coated hard plastic or glass with fibronectin or with collagen 4 and then looked

at the motility of cells. And what you see here is the function of the density of these

proteins, the coating density. They found a bimodal response of the cells. So when the

coating density is lower, the cells can't really adhere well, and so the cells don't

move or very little. If you now increase the density of adhesion ligands on the substrate,

the percentage of motile cells increases and their speed increases. But if you make them

essentially too adhesive, then this decreases again. So cells, when it's too adhesive, can't

move, they get, if you wish, they get glued to their spot. And of course it does matter

whether we have fibronectin or collagen as an adhesive ligand. For collagen, you need

higher densities of the protein in order to get this bimodal response. But you see it

also in collagen. And essentially, the reason of the interpretation is that when the adhesiveness

gets too large, cells sort of become stuck. They can't really resolve their adhesions