There are many ways we can study how the cells migrate in the lab. A typical migration experiment goes something like this: You have your cells, you coat the surface where you want your cells to migrate on with a matrix proteins-the kind of proteins that are needed for the cells to adhere to, and you seed your cells on top. So typically the surface you choose is the petri dish, flat like a TV. And your cells are fine, they are happy just where they are, they migrate very nicely on top of this matrix too. They look something like this:
Above is an Ewing sarcoma cancer cell migrating on a fibronectin matrix. Fibronectin is a type of matrix proteins that are found in many places in your body, such as at a closing wound, or inside a blood clot. Many cells can adhere or stick to fibronectin through the use of receptor molecules on their surface known as Integrins, but this is a story for another day. I took this video using a special microscope called a timelapse microscope. It snaps each picture every few minutes, and then put them all together into a sequence and you got yourself a vide of a moving cell, something similar to a stop-motion movie if you know. Anyway, as you can see, the cell is quite flat and it migrates very fast, almost like gliding on top of the surface. This type of experiment is very useful for us to understand the most basic property of cell migration, like the morphology, how fast they move, and where do they move. And some of the cells in our body do this kind of 2D migration too, like those epithelial cells migrating on the surface of your wound to close it, not entirely the same but close enough example. And when we stain these 2D cells with different antibodies and fluorescent molecules called immunofluorescence to visualise what's inside or outside the cell, we got something like the image below:
Quite pretty huh? The round structure is the nucleus, the yellow-ish at the rim is our favourite protein Arp2/3 that I mentioned in my first blog, and the magenta is the Integrin molecules i mentioned earlier that help stick the cell on to a surface and allow them to move around. So 2D is quite useful in this way, it's easy and we can do a lot of things with it, we can learn a lot of things about the cells.
BUT, yep, there's always the but. Inside our body, most of the cells don't look flat like this! They are more likely to be surrounding in a matrix from all different angles, above, below, two sides or 3D. So instead of gliding nicely like this, the cells will have to wiggle around a lot, because now there's so much stuff on the way, a lot of crisscrossing matrix and no longer an open space like on a flat 2D surface anymore. Your macrophages (a type of immune cells involved in eating bacteria and dead cells) will need to wiggle through the maze of matrix underneath your skin to get to where the wound is to defence your body. Or during a pathological process such as metastasis, the cancer cells actually have to do the same in order to invade into the surrounding or get into the bloodstream to metastasize to a distant organ in your body. So it's actually very helpful if we can see how do these cells look like when they are in 3D, and maybe we can figure out how they move in such complex environment, how they interact with their surroundings and maybe we can interfere with the bad stuff like cancer and help with the good stuff like your immune cells. But of course, studying 3D is a little bit more tricky than 2D and working with it can be less convenient. But in the lab, we got different tricks up our sleeves to help us pierce into these 3D processes easier. One way is to make a 3D substrate! So when a wound is healing, a type of cells migrate and deposit matrix to seal off the wound known as fibroblasts. And we can actually grow these fibroblasts, let them make their matrix and then kill them off but leaving the matrix intact, and we call it cell-derived matrix or CDM. The matrix is thick enough to cover the cells in all different directions and can recapitulate a 3D environment. But at the same time, this matrix is not too thick that would still allow us to study the cells in it easily.
So what does the cell I show you above look like now in this new 3D matrix? Well here it is:
Wow, it looks different, right? They are the exact same cell type, but now you can see the cell in 3D have so many spikes, or we call protrusions. These protrusions we believe can help them move like little feet, but also help them to feel around like little hands. We call them filopodia, with "filo" means threads, and "podia" means feet. The cell here is also glowing in the dark, we call it fluorescent because we have put a fluorescently-labelled protein in the cell to help us see it with a microscope. If we colour each frame of the movie with a different colour and then overlay them on top each other, we can see how dynamic these filopodia are, as you can see in the image below:
Pretty huh? Not every cell have this many protrusions, but this is a cancer cell, a very migratory one so they have many of these feet to help them move around better. This 3D look gives us scientists a better and closer look at how cells are like in a more native environment and we can then study what does the environment do to them. There are many more ways to make a 3D model and study the cell, but this is one of them and it's pretty cool!
So here you have it, 2D vs 3D. Both have their pros and cons but hey diversity is what makes us complete :)
Until next time.
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