Project description:Quiescent stem cells are periodically activated to maintain tissue homeostasis or occasionally called into action upon injury. Molecular mechanisms that constitutively maintain stem cell identity or promote stem cell proliferation and differentiation upon activation have been extensively studied. However, it is unclear how quiescent stem cells maintain identity and reinforce quiescence when they transition from quiescence to activation. Here we show mouse hair follicle stem cell compartment induces a transcription factor, Foxc1, when activated. Importantly, deletion of Foxc1 in the activated but not quiescent stem cells compromises stem cell identity, fails to re-establish quiescence and subsequently drives premature stem cell activation.These findings uncover a dynamic, cell-intrinsic mechanism employed by hair follicle stem cells to reinforce stemness in response to activation. Poly(A)-enriched transcriptome RNA-seq on HFSCs isolated in WT and K14Cre cKO mice at anagen and early telogen stage of hair cycle.
Project description:Quiescent stem cells are periodically activated to maintain tissue homeostasis or occasionally called into action upon injury. Molecular mechanisms that constitutively maintain stem cell identity or promote stem cell proliferation and differentiation upon activation have been extensively studied. However, it is unclear how quiescent stem cells maintain identity and reinforce quiescence when they transition from quiescence to activation. Here we show mouse hair follicle stem cell compartment induces a transcription factor, Foxc1, when activated. Importantly, deletion of Foxc1 in the activated but not quiescent stem cells compromises stem cell identity, fails to re-establish quiescence and subsequently drives premature stem cell activation.These findings uncover a dynamic, cell-intrinsic mechanism employed by hair follicle stem cells to reinforce stemness in response to activation.
Project description:Quiescent stem cells are periodically activated to maintain tissue homeostasis or occasionally called into action upon injury. Molecular mechanisms that constitutively maintain stem cell identity or promote stem cell proliferation and differentiation upon activation have been extensively studied. However, it is unclear how quiescent stem cells maintain identity and reinforce quiescence when they transition from quiescence to activation. Here we show mouse hair follicle stem cell compartment induces a transcription factor, Foxc1, when activated. Importantly, deletion of Foxc1 in the activated but not quiescent stem cells compromises stem cell identity, fails to re-establish quiescence and subsequently drives premature stem cell activation.These findings uncover a dynamic, cell-intrinsic mechanism employed by hair follicle stem cells to reinforce stemness in response to activation.
Project description:In many organs, adult stem cells are uniquely poised to serve as cancer cells of origin. In the epidermis, hair follicle stem cells (HFSCs) cycle through stages of quiescence (telogen) and proliferation (anagen) to drive hair growth. Within the hair follicle, HFSCs are capable of initiating squamous cell carcinoma, yet it is unclear how the hair cycle contributes to tumorigenesis. The data presented here show that HFSCs are unable to initiate tumors during the quiescent phase of the hair cycle, indicating that the mechanisms that keep HFSCs dormant are dominant to gain of oncogenes (Ras) or loss of tumor suppressors (p53). Instead, prolonged oncogenic stimuli only exert their effects when HFSC quiescence mechanisms are removed by normal HFSC activation. Furthermore, Pten activity is necessary for quiescence based tumor suppression, since Pten deletion alleviates this stem cell specific ability without affecting proliferation per se. Small RNAs were cloned from Trizol-lysed cells sorted from mouse skin and sequenced with the Illumina HiSeq2000.
Project description:In many organs, adult stem cells are uniquely poised to serve as cancer cells of origin. In the epidermis, hair follicle stem cells (HFSCs) cycle through stages of quiescence (telogen) and proliferation (anagen) to drive hair growth. Within the hair follicle, HFSCs are capable of initiating squamous cell carcinoma, yet it is unclear how the hair cycle contributes to tumorigenesis. The data presented here show that HFSCs are unable to initiate tumors during the quiescent phase of the hair cycle, indicating that the mechanisms that keep HFSCs dormant are dominant to gain of oncogenes (Ras) or loss of tumor suppressors (p53). Instead, prolonged oncogenic stimuli only exert their effects when HFSC quiescence mechanisms are removed by normal HFSC activation. Furthermore, Pten activity is necessary for quiescence based tumor suppression, since Pten deletion alleviates this stem cell specific ability without affecting proliferation per se.
Project description:In some organs, adult stem cells are uniquely poised to serve as cancer cells of origin1-4. It is unclear, however, whether tumorigenesis is influenced by the activation state of the adult stem cell. Hair follicle stem cells (HFSCs) act as cancer cells of origin for cutaneous squamous cell carcinoma (SCC) and undergo defined cycles of quiescence and activation. The data presented here show that HFSCs are unable to initiate tumors during the quiescent phase of the hair cycle, indicating that the mechanisms that keep HFSCs dormant are dominant to the gain of oncogenes (Ras) or the loss of tumor suppressors (p53). Furthermore, Pten activity is necessary for quiescence based tumor suppression, as its deletion alleviates tumor suppression without affecting proliferation. These data demonstrate that stem cell quiescence is a form of tumor suppression in HFSCs, and that Pten plays a role in maintaining quiescence in the presence of tumorigenic stimuli. This experiment includes RNA profiling of hair follicle stem cells at various stages of tumorigenesis
Project description:DNA damage represents one of the cell intrinsic causes of stem cell aging, which leads to differentiation induced removal of damaged stem cells in skin and blood. Dietary restriction (DR) retards aging across various species including several strains of laboratory mice. Whether, DR has the potential to ameliorate DNA damage driven stem cell exhaustion remains incompletely understood. Here, we show that DR strongly extends the time to hair graying in response to γ–irradiation (IR) induced DNA damage of C57BL/6J mice. The study shows that DR prolongs quiescence of hair follicle stem cells (HFSCs) by silencing gene regulatory networks and metabolic switches that control proliferation and tissue regeneration. DR-mediated prolongation of HSFC quiescence blocks hair growth and prevents the depletion of HFSCs and ckit+ melanoblasts in response to IR. However, prolongation of HSFCs quiescence also leads to a suppression of DNA repair pathways and cannot prevent melanoblast loss and hair graying in the long run, when hair cycling is re- initiated even after extended periods of time. Together, these results support a model indicating that nutrient deprivation can delay but not heal DNA damage driven extinction of HFSCs and melanoblasts by stalling HSFCs in a prolonged state of quiescence coupled with inhibition of DNA repair. Disconnecting these two types of responses to DR could have the potential to delay stem cell aging.
Project description:Mouse back skin was disassociated to single cells, sorted by cell surface markers and tested by microarrray To compare the gene expression of mouse bulge (CD34+CD200+CD49+) versus secondary hair germ (CD34-CD200+CD49+) versus interfollicular epidermis (CD34-CD200-CD49+) xx Bald scalp retains hair follicle stem cells but lacks CD200-rich and CD34-positive hair follicle progenitor cells Androgenetic alopecia (AGA) or common baldness results from a marked decrease in hair follicle size. This miniaturization may be related to loss of hair follicle stem or progenitor cells. To test this hypothesis, we analyzed bald and non-bald scalp from the same individuals for the presence of hair follicle stem and progenitor cells using flow cytometry to quantitate cells expressing CYTOKERATIN 15 (KRT15), CD200, CD34 and ALPHA-6-INTEGRIN (ITGA6). High levels of KRT15 expression correlated with stem cell properties of small cell size and quiescence. Cells with the highest level of KRT15 expression were maintained in bald scalp; however, distinct populations of CD200high ITGA6high cells and CD34-positive cells were markedly diminished. Consistent with a progenitor cell phenotype, the diminished populations localized closely to the stem-cell rich bulge area but were larger and more proliferative than the bulge stem cells. In functional assays, analogous CD200 high /Itga6 high cells from murine hair follicles were multipotent and generated new hair follicles in skin reconstitution assays. These findings suggest that a defect in stem cell activation plays a role in the pathogenesis of AGA. 4 independent biologic replicates (each pooled from 3 distinct mice) were sorted for Mouse bulge (CD34+CD200+CD49+) versus secondary hair germ (CD34-CD200+CD49+) versus interfollicular epidermis (CD34-CD200-CD49+)
Project description:Piloerection (goosebump) requires concerted actions of the hair follicle, the arrector pili muscle (APM), and the sympathetic nerve, providing a model to study interactions across epithelium, mesenchyme, and nerves. Here, we show that APMs and sympathetic nerves form a dual component niche to modulate hair follicle stem cell (HFSC) activity. Sympathetic nerves form synapse-like structures with HFSCs and regulate HFSCs through norepinephrine, whereas APMs maintain sympathetic innervation to HFSCs. Without norepinephrine signaling, HFSCs enter a deep quiescence state by down-regulating cell cycle machinery and mitochondria metabolism, while up-regulating quiescence regulators Lhx2, Foxp1, and Fgf18. During development, HFSC progeny secrets Sonic Hedgehog (SHH) to direct the formation of this APM-sympathetic nerve niche, which in turn controls hair follicle regeneration in adults. Our results reveal a reciprocal interdependence between a regenerative tissue and its niche at different stages, and illustrate that nerves can modulate stem cell quiescence through synapses and neurotransmitters.