STEM CELLS & SUBSTRATES
Contemporary investigations in cell biology have revealed just how important the extracellular environment is to intracellular function. This is especially true with pluripotent stem cells – progenitor cells that possess the ability to mature into a variety of cell types. For instance, skeletal muscle stem cells ordinarily go about their business and differentiate into muscle cells, but under the right circumstances, these cells can potentially differentiate into adipocytes, or neurons, or fibroblasts, or many other varieties of mature cell types, all as a result of environmental modification.
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Recent research shows that simply modifying the stiffness of the underlying substrate can be enough to prompt pluripotent stem cells to mature down a specific cell line. Cells grown on soft substrate, mimicking the texture of nervous tissue, often go on to become neurons themselves. In other cases, cells grown on stiff substrates, mimicking that of muscle tissue, go on to become muscle cells as a result. The subtle influence of the ground substrate can have drastic effects on the lineage of the cells that grow atop its surface. Interactions between the cell and its surrounding environment play an important role in cell behavior.
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Applying this knowledge to cancer cells might explain how and why metastatic events take place. A cancerous cell from an initial tumor might naturally undergo a process by which it detaches from its neighboring cells as a result of contact with a particular tissue type. Later on, that same cell might attach to some other tissue type, giving rise to a new tumor elsewhere in the body. By better understanding the process by which cells cling to and interact with their immediate environments, further research might reveal new ways to prevent metastatic events from occurring altogether.
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A colleague and I took interest in this research, and designed an experiment to test the strength of these extracellular structures. In this experiment, we cultured skeletal muscle stem cells from rats, and subjected these cells to increasing degrees of shear stress, which in our case was a vortex of fast moving water. We wanted to see whether or not the focal adhesion sites between the cells and the underlying substrate were stronger than the cytoskeletal filaments of the cell itself. Below is a small gallery of my favorite images captured from this experiment. We used immunofluorescent antibodies to stain for the following features in our test cells:
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Paxillin (green) - A key protein that composes focal adhesion points. The green dots indicate locations where a junction exists between the cell and its underlying substrate.
Fibronectin (red) - A structural protein that makes up part of the cytoskeleton. These fibers are a good indicator of where the bulk of a cell body lies.
DAPI (blue) - This stain targets DNA. Any cells in the images below with a bright, blue center have an intact nucleus.
Our results indicated a mix of intact cells still holding on for dear life amongst various focal adhesions and small bits of cells that were left behind. We believe this result indicates that focal adhesion points might be even stronger than cytoskeletal filaments.
