The in vitro organoid model is a major technological breakthrough that has already been established as an essential tool in many basic biology and clinical applications. This near-physiological 3D ...model facilitates an accurate study of a range of in vivo biological processes including tissue renewal, stem cell/niche functions and tissue responses to drugs, mutation or damage. In this Review, we discuss the current achievements, challenges and potential applications of this technique.
Molecular markers are used to characterize and track adult stem cells. Colon cancer research has led to the identification of 2 related receptors, leucine-rich repeat–containing, G-protein–coupled ...receptors (Lgr)5 and Lgr6, that are expressed by small populations of cells in a variety of adult organs. Genetic mouse models have allowed the visualization, isolation, and genetic marking of Lgr5+ve and Lgr6+ve cells and provided evidence that they are stem cells. The Lgr5+ve cells were found to occupy locations not commonly associated with stem cells in the stomach, small intestine, colon, and hair follicles. A multipotent population of skin stem cells express Lgr6. Single Lgr5+ve stem cells from the small intestine and the stomach can be cultured into long-lived organoids. Further studies of these markers might reveal adult stem cell populations in additional tissues. Identification of the ligands for Lgr5 and 6 will help elucidate stem cell functions and modes of intracellular signaling.
Limited pools of resident adult stem cells are critical effectors of epithelial renewal in the intestine throughout life. Recently, significant progress has been made regarding the isolation and in ...vitro propagation of fetal and adult intestinal stem cells in mammals. It is now possible to generate ever-expanding, three-dimensional epithelial structures in culture that closely parallel the in vivo epithelium of the intestine. Growing such organotypic epithelium ex vivo facilitates a detailed description of endogenous niche factors or stem-cell characteristics, as they can be monitored in real time. Accordingly, this technology has already greatly contributed to our understanding of intestinal adult stem-cell renewal and differentiation. Transplanted organoids have also been proven to readily integrate into, and effect the long-term repair of, mouse colonic epithelia in vivo, establishing the organoid culture as a promising tool for adult stem cell/gene therapy. In another exciting development, novel genome-editing techniques have been successfully employed to functionally repair disease loci in cultured intestinal stem cells from human patients with a hereditary defect. It is anticipated that this technology will be instrumental in exploiting the regenerative medicine potential of human intestinal stem cells for treating human disorders in the intestinal tract and for creating near-physiological ex vivo models of human gastrointestinal disease.
Aberrant activation of the Wnt pathway is implicated in driving the formation of various human cancers, particularly those of the digestive tract. Inhibition of aberrant Wnt pathway activity in ...cancer cell lines efficiently blocks their growth, highlighting the great potential of therapeutics designed to achieve this in cancer patients. Here we provide an overview of the promise and pitfalls of current drug development strategies striving to inhibit the Wnt pathway and present new opportunities for therapeutic intervention.
The mammalian ovary is covered by a single-layered epithelium that undergoes rupture and remodelling following each ovulation. Although resident stem cells are presumed to be crucial for this cyclic ...regeneration, their identity and mode of action have been elusive. Surrogate stemness assays and in vivo fate-mapping studies using recently discovered stem cell markers have identified stem cell pools in the ovary and fimbria that ensure epithelial homeostasis. Recent findings provide insights into intrinsic mechanisms and local extrinsic cues that govern the function of ovarian and fimbrial stem cells. These discoveries have advanced our understanding of stem cell biology in the ovary and fimbria, and lay the foundations for evaluating the contribution of resident stem cells to the initiation and progression of human epithelial ovarian cancer.
Small populations of adult stem cells are responsible for the remarkable ability of the epithelial lining of the intestine to be efficiently renewed and repaired throughout life. The recent discovery ...of specific markers for these stem cells, together with the development of new technologies to track endogenous stem cell activity in vivo and to exploit their ability to generate new epithelia ex vivo, has greatly improved our understanding of stem cell-driven homeostasis, regeneration and cancer in the intestine. These exciting new insights into the biology of intestinal stem cells have the potential to accelerate the development of stem cell-based therapies and ameliorate cancer treatments.
Decades ago, two nonoverlapping crypt stem cell populations were proposed: Leblond’s Crypt Base Columnar (CBC) cell and Potten’s +4 cell. The identification of CBC markers including Lgr5 has ...confirmed Leblond’s predictions that CBC cells are anatomically distinct, long-lived stem cells that permanently cycle. While Potten originally described +4 cells as proliferative and unusually radiation-sensitive, recent efforts to identify +4 stem cells have focused on the identification of cells that are quiescent and radiation-resistant. Here, we describe commonalities and discrepancies between the individual studies and discuss challenges of marker-based lineage tracing.
The ultimate success of global efforts to exploit adult stem cells for regenerative medicine will depend heavily on the availability of robust, highly selective stem cell surface markers that ...facilitate the isolation of stem cells from human tissues. Any subsequent expansion or manipulation of isolated stem cells will also require an intimate knowledge of the mechanisms that regulate these cells, to ensure maintenance of their regenerative capacities and to minimize the risk of introducing undesirable growth traits that could pose health risks for patients. A subclass of leucine-rich repeat-containing G-protein-coupled receptor (Lgr) proteins has recently gained prominence as adult stem cell markers with crucial roles in maintaining stem cell functions. Here, we discuss the major impact that their discovery has had on our understanding of adult stem cell biology in various self-renewing tissues and in accelerating progress towards the development of effective stem cell therapies.
The intestinal stem cell Barker, Nick; van de Wetering, Marc; Clevers, Hans
Genes & development,
07/2008, Letnik:
22, Številka:
14
Journal Article
Recenzirano
Odprti dostop
The epithelium of the adult mammalian intestine is in a constant dialog with its underlying mesenchyme to direct progenitor proliferation, lineage commitment, terminal differentiation, and, ...ultimately, cell death. The epithelium is shaped into spatially distinct compartments that are dedicated to each of these events. While the intestinal epithelium represents the most vigorously renewing adult tissue in mammals, the stem cells that fuel this self-renewal process have been identified only recently. The unique epithelial anatomy makes the intestinal crypt one of the most accessible models for the study of adult stem cell biology. This review attempts to provide a comprehensive overview of four decades of research on crypt stem cells.
Wnt/β-catenin signaling is integral to the homeostasis and regeneration of many epithelial tissues due to its critical role in adult stem cell regulation. It is also implicated in many epithelial ...cancers, with mutations in core pathway components frequently present in patient tumors. In this chapter, we discuss the roles of Wnt/β-catenin signaling and Wnt-regulated stem cells in homeostatic, regenerative and cancer contexts of the intestines, stomach, skin, and liver. We also examine the sources of Wnt ligands that form part of the stem cell niche. Despite the diversity in characteristics of various tissue stem cells, the role(s) of Wnt/β-catenin signaling is generally coherent in maintaining stem cell fate and/or promoting proliferation. It is also likely to play similar roles in cancer stem cells, making the pathway a salient therapeutic target for cancer. While promising progress is being made in the field, deeper understanding of the functions and signaling mechanisms of the pathway in individual epithelial tissues will expedite efforts to modulate Wnt/β-catenin signaling in cancer treatment and tissue regeneration.
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