Stem cells have both the capacity to self-renew, that is, to divide and create additional stem cells, and also to...
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Stem cells have both the capacity to self-renew, that is, to divide and create additional stem cells, and also to differentiate along a specified molecular pathway. Embryonic stem cells are very nearly totipotent, reserving the elite privileges of choosing among most if not all of the differentiation pathways that specify the animal. In contrast, stem cells that reside within an adult organ or tissue have more restricted options, often able to select a differentiation program from only a few possible pathways, which still can make them valuable for tissue regeneration in a clinical setting. Long-standing examples of such successes include bone marrow transplants in immune disorders, including cancers, and skin culture grafts to replace epidermis damaged from burns. My laboratory studies the stem cells of the skin that can make epidermis, sebaceous glands and hair follicles. Although only the thickness of cellophane, the epidermis of the skin is responsible for providing protection against harmful microbes and for preventing the evaporation of our essential body fluids. Being at the skin surface, epidermal cells are constantly exposed to wear and tear. Yet they keep regenerating, due to a supply of active stem cells, which create a new epidermis every 4 weeks throughout the course of a lifetime. Skin stem cells also account for why our hairs fall out but regrow, and why our body surface is lubricated with fresh oils and sweat. In this lecture, I discuss the differences between embryonic and adult stem cells, the controversies involved, and their potential for regenerative medicine. Using skin as a model system, I explore the fascinating features of adult stem cells, how they choose among different lineages and how they repair tissues damaged during injury.
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