Our body’s largest organ, the skin, regenerates itself on a weekly basis. To accomplish this goal, it maintains a self-renewing population of stem cells that can become the many different types of cells found within the skin. This self-renewal, however, must be tightly regulated because uncontrolled cell division can lead to disease like cancer. Investigators at Yale University have uncovered how the stem cell population as a whole controls this critical process. Their work was published in Cell Stem Cell last week.
One of the limitations to studying this population of self-renewing stem cells was the inability to simultaneously track a stem cell’s ability to undergo self-renewal or differentiation into a mature skin cell. Using an innovative form of spatio-temoral live imaging of individual stem cells in mice, the investigators found that death or differentiation of neighboring cells caused stem cells to undergo self-renewal. Interestingly, they found that this process was unidirectional, meaning that differentiation of a stem cell can lead to division, or self-renewal, of a neighboring cell, but self-renewal does not trigger differentiation in surrounding cells.
This finding is particularly interesting, because it indicates a shift in homeostatic mechanisms in developing skin versus adult skin. In an embryo, differentiation of stem cells regulates the differentiation of surrounding cells, whereas, in the adult epidermis, it appears that neighboring cells are responsible for promoting self-renewal of the stem cell population. The investigators confirmed their conclusions by experimentally forcing stem cells to differentiate and found that this induced neighboring cells to divide and undergo self-renewal.
These findings provide important insight into the basic biology behind stem cell renewal in one of our most dynamic organs, the skin.