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Many reptiles are able to continuously replace their teeth through life, an ability attributed to the existence of epithelial stem cells. Tooth replacement occurs in a spatially and temporally regulated manner, suggesting the involvement of diffusible factors, potentially over long distances. Here, we locally disrupted tooth replacement in the leopard gecko (Eublepharis macularius) and followed the recovery of the dentition. We looked at the effects on local patterning and functionally tested whether putative epithelial stem cells can give rise to multiple cell types in the enamel organs of new teeth. Second generation teeth with enamel and dentine were removed from adult geckos. The dental lamina was either left intact or disrupted in order to interfere with local patterning cues. The dentition began to reform by 1 month and was nearly recovered by 2–3 months as shown in μCT scans and eruption of teeth labeled with fluorescent markers. Microscopic analysis showed that the dental lamina was fully healed by 1 month. The deepest parts of the dental lamina retained odontogenic identity as shown by PITX2 staining. A pulse-chase was carried out to label cells that were stimulated to enter the cell cycle and then would carry BrdU forward into subsequent tooth generations. Initially we labeled 70–78% of PCNA cells with BrdU. After a 1-month chase, the percentage of BrdU + PCNA labeled cells in the dental lamina had dropped to 10%, consistent with the dilution of the label. There was also a population of single, BrdU-labeled cells present up to 2 months post surgery. These BrdU-labeled cells were almost entirely located in the dental lamina and were the likely progenitor/stem cells because they had not entered the cell cycle. In contrast fragmented BrdU was seen in the PCNA-positive, proliferating enamel organs. Homeostasis and recovery of the gecko dentition was therefore mediated by a stable population of epithelial stem cells in the dental lamina.

Adult tissues contain label-retaining cells (LRCs), which are relatively slow-cycling and considered to represent a property of tissue stem cells (SCs). In the ocular surface epithelium, LRCs are present in the limbus and conjunctival fornix; however, the character of these LRCs remains unclear, owing to lack of appropriate molecular markers. Using three CreER transgenic mouse lines, we demonstrate that the ocular surface epithelium accommodates spatially distinct populations with different cell division dynamics. In the limbus, long-lived Slc1a3CreER-labeled SCs either migrate centripetally toward the central cornea or slowly expand their clones laterally within the limbal region. In the central cornea, non-LRCs labeled with Dlx1CreER and K14CreER behave as short-lived progenitor cells. The conjunctival epithelium in the bulbar, fornix and palpebral compartment is regenerated by regionally unique SC populations. Severe damage to the cornea leads to the cancellation of SC compartments and conjunctivalization, whereas milder limbal injury induces a rapid increase of laterally expanding clones in the limbus. Taken together, our work defines compartmentalized multiple SC/progenitor populations of the mouse eye in homeostasis and their behavioral changes in response to injury., Summary: This study provides genetic tools to precisely mark and examine the dynamic behavior of heterogeneous stem cell populations in the ocular surface epithelium.

Label-retaining cells, which are characterized by dormancy or slow cycling, may be identified in a number of human normal and cancer tissues, and these cells demonstrate stem cell potential. In glioblastoma, label-retaining assays to enrich glioma stem cells remain to be fully investigated. In the present study, glioblastoma sphere cells cultured in serum-free medium were initially stained with the cell membrane fluorescent marker DiI. The fluorescence intensity during cell proliferation and sphere reformation was observed. At 2 weeks, the DiI-retaining cells were screened by fluorescence-activated cell sorting and compared phenotypically with the DiI-negative cells in terms of in vitro proliferation, clonogenicity and multipotency and for in vivo tumorigenicity, as well as sensitivity to irradiation and temozolomide treatment. It was observed that DiI-retaining cells accounted for a small proportion

International audience; : BackgroundIt is well established that inflammation promotes cancer, including melanoma, although the exact mechanisms involved are less known. In this study, we tested the hypothesis that inflammatory factors affect the cancer stem cell (CSC) compartment responsible for tumor development and relapse.ResultsUsing an inducible histone 2B-GFP fusion protein as a tracer of cell divisional history, we determined that tumor necrosis factor (TNF), which is a classical pro-inflammatory cytokine, enlarged the CSC pool of GFP-positive label-retaining cells (LRCs) in tumor-like melanospheres. Although these cells acquired melanoma stem cell markers, including ABCB5 and CD271, and self-renewal ability, they lost their capacity to differentiate, as evidenced by the diminished MelanA expression in melanosphere cells and the loss of pigmentation in a skin equivalent model of human melanoma. The undifferentiated cell phenotype could be reversed by LY294002, which is an inhibitor of the PI3K/AKT signaling pathway, and this reversal was accompanied by a significant reduction in CSC phenotypic markers and functional properties. Importantly, the changes induced by a transient exposure to TNF were long-lasting and observed for many generations after TNF withdrawal.ConclusionsWe conclude that pro-inflammatory TNF targets the quiescent/slow-cycling melanoma SC compartment and promotes PI3K/AKT-driven expansion of melanoma SCs most likely by preventing their asymmetrical self-renewal. This TNF effect is maintained and transferred to descendants of LRC CSCs and is manifested in the absence of TNF, suggesting that a transient exposure to inflammatory factors imprints long-lasting molecular and/or cellular changes with functional consequences long after inflammatory signal suppression. Clinically, these results may translate into an inflammation-triggered accumulation of quiescent/slow-cycling CSCs and a post-inflammatory onset of an aggressive tumor.

We have identified some unusually persistent label-retaining cells in the hair follicles of mice, and have investigated their role in hair growth. Three-dimensional reconstruction of dorsal underfur follicles from serial sections made 14 mo after complete labeling of epidermis and hair follicles in neonatal mice disclosed the presence of highly persistent label-retaining cells associated with the first-generation follicle involved in the production of the first wave of hairs, commonly called the bulge. The label-retaining cells were most often found on the ventral surface of the first-generation follicle, five cell positions from the base, near the attachment site of the arrector pilorum muscle. No label-retaining cells were found in the hair canal, sebaceous gland, or hair germ. These label-retaining cells remained in the follicle following induction of anagen by plucking of the hairs. Surprisingly, they were not part of the first wave of mitotic activity following plucking, but instead underwent mitosis beginning 42 h after plucking. Label-retaining cells or their labeled daughters were not found in the hair germs through 48 h following induction of anagen by plucking, but instead remained in their subsebaceous follicular location even upon completion of the hair growth cycle 21 d later. These label-retaining cells are, therefore, unlikely to contribute to the formation of a new anagen follicle.