The role of Cbx4/Polycomb-2 in epidermal stem cell homeostasis.
Human epidermis relies on a population of adult stem cells to maintain its homeostasis. Stem cells transit from a dormant to an active state and undergo a tightly regulated process of differentiation that replenishes the tissue according to its needs. This process either replaces cells that get shed...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2011 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/53063 |
| Acceso en línea: | http://hdl.handle.net/10803/53063 |
| Access Level: | acceso abierto |
| Palabra clave: | Human epidermal stem cells Polycomb proteins Cbx4/hPC2 chromatin remodeling Transition from stem cell dormancy and activation Stem cell senescense Células troncales adultas humanas Remodelación de la cromatina Homeostasis de la epidermis Senescencia de células troncales 576 |
| Sumario: | Human epidermis relies on a population of adult stem cells to maintain its homeostasis. Stem cells transit from a dormant to an active state and undergo a tightly regulated process of differentiation that replenishes the tissue according to its needs. This process either replaces cells that get shed away, or contributes to tissue healing upon injuries, such as wounding. Distinct molecular mechanisms are required to keep human epidermal stem cells localized in their niche and for their active proliferation and mobilization, while others regulate their differentiation status. However, little is known about the proper global chromatin modifications that ensure the correct transition between these stem cell states. This work shows that Cbx4, a Polycomb Repressive Complex-1 (PRC1)-associated protein, maintains human epidermal stem cells slow-cycling and undifferentiated, while protecting them from senescence. Interestingly, abrogating the polycomb activity of Cbx4 impairs its anti-senescent function without affecting stem cell differentiation, indicating that differentiation and senescence are independent processes in human epidermis. Conversely, Cbx4 inhibits stem cell activation and differentiation through its SUMO ligase activity. Global transcriptome and chromatin occupancy analyses indicate that Cbx4 regulates modulators of epidermal homeostasis and represses factors, such as Ezh2, Dnmt1, and Bmi1, to prevent the active stem cell state. Interestingly, Cbx4 also represses genes required for neuronal fate repression, suggesting that it might have a role in ectoderm patterning during development. Cbx proteins are differently expressed during epidermal differentiation and the activity of Cbx4 towards promoting human epidermal stem cell quiescence is unique among the Cbx proteins. This suggests that different Polycomb complexes are assembled, based on the availability of its core member, and balance epidermal stem cell dormancy and activation, while continually preventing senescence and differentiation. |
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