On the basis of these studies, McSCs in the bulge are postulated to represent long-term stem cells 6. Furthermore, McSCs in the bulge cycle more slowly than those in the HG during HF regeneration 6. Similar to HG epithelial cells, HG McSCs activate WNT signalling and undergo differentiation at the onset of regeneration 7. At the onset of the anagen growth phase, McSCs regenerate differentiated melanocytes that migrate downwards into the hair bulb, where they produce pigment for the hair. McSCs are located in the bulge and hair germ (HG) area in telogen-phase hair follicles (HFs) 4, 5, where they are surrounded by HF epithelial stem cells (bulge cells) 14 and progenitor cells (HG cells) 15, 16 that constitute to the McSC niche. The organization of the McSC system, responsible for hair pigmentation, is thought to parallel that of hair follicle stem cells (HFSCs) 5, 6, 7, 8. In this model, the life-long durability of self-renewing tissues is typically sustained by a functionally and molecularly heterogeneous pool of stem and progenitor cells. This theory proposes that stem cells (undifferentiated state) have two distinct fates: one to sustain themselves through self-renewal and the second to produce transit-amplifying (TA) progeny (intermediate differentiated state) that ultimately give rise to functional differentiated cells during tissue regeneration 12, 13, 14. Stem cell differentiation is generally viewed as unidirectional and follows the hierarchical model originally established through the study of haematopoietic stem cells 9, 10, 11. Mammalian tissue regeneration largely depends on the capacity of adult stem cells to differentiate. These results identify a new model whereby dedifferentiation is integral to homeostatic stem cell maintenance and suggest that modulating McSC mobility may represent a new approach for the prevention of hair greying. During ageing, there is accumulation of stranded McSCs that do not contribute to the regeneration of melanocyte progeny. Long-term lineage tracing demonstrated that the McSC system is maintained by reverted McSCs rather than by reserved stem cells inherently exempt from reversible changes. Live imaging and single-cell RNA sequencing revealed that McSCs are mobile, translocating between hair follicle stem cell and transit-amplifying compartments where they reversibly enter distinct differentiation states governed by local microenvironmental cues (for example, WNT). Here we show that most McSCs toggle between transit-amplifying and stem cell states for both self-renewal and generation of mature progeny, a mechanism fundamentally distinct from those of other self-renewing systems. Current dogma states that McSCs are reserved in an undifferentiated state in the hair follicle niche, physically segregated from differentiated progeny that migrate away following cues of regenerative stimuli 4, 5, 6, 7, 8. We welcome your feedback.For unknow reasons, the melanocyte stem cell (McSC) system fails earlier than other adult stem cell populations 1, which leads to hair greying in most humans and mice 2, 3. We seek to connect those looking for information about the various types of stem cell research with the science and the experiences of those who’ve lived it. Stem Cell Connect is not a clinic, has no doctors and performs no stem cell transplants. My Experience is a place where we give transplant recipients the time to share their personal experiences with a little more depth. Our Success Stories come from people who have experienced a successful adult stem cell transplant. This is still an educational web site created with the goal of connecting stem cell science, patients and stories. We feature an in-depth look at the subject on our front page. While researchers, doctors and the public continue to debate the ethical questions raised, there is little doubt that science and clinical treatments are moving away from embryonic and toward adult and induced pluripotent(iPS) stem cell research. The field of stem cell research has evolved dramatically in the past 20 years. Welcome to Stem Cell Research Facts and Stem Cell Connect.
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