In the movie Nacho Libre', Nacho is a wrestler (luchador) and likes to wear the "stretchy" pants the luchadors wear. Living things made out of cells can be very firm like plant structures, but in animals, cells are very stretchy and can participate in making structures like human skin and other tissues which are very malleable. In our next topic in class we will discuss how eukaryotic tissue cells communicate with the outside world. Certain outside stimuli involving the extracellular matrix can promote shape change in cells and it can cause them to stretch and contort in ways that seem extreme. Some cells must be stretched and shaped in order to form the shape of internal organs and for wound healing. How do you stretch a cell and not break it? Answer: very carefully.
In a recent paper in Nature, a mechanism for stretching cells is proposed. The mechanism centers around fascinating membrane protein complexes called hemidesmosomes. Hemidesmosomes have been known for quite some time to be attachment structures which attach cells to other cells or the extracellular matrix. Hemidesmosomes also attach to cytoskeleton components inside cells. But new studies suggest that hemidesmosomes are also mechanosensors able to detect outside forces which squeeze and stretch cells. Hemidesmosomes communicate with intracellular cell signaling components such as kinases and other proteins. Here again we have another case where a protein is involved in multiple functions. The end result of the squeezing and stretching is elongated cells that contribute to the final shape of an internal organ for example during embryogenesis.
1 Review hemidesmosome structure and suggest a mechanism for how they could be involved in cell stretching?
2 What would be the overal mechanism that would drive the cells to take on shapes which would contribute to the final morphology of an internal organ?
3 How do cells know how much force they can take before they rip apart?