The historical reliance of biological research on the use of animal models has sometimes made it challenging to address questions that are specific to the understanding of human biology and disease. ...But with the advent of human organoids - which are stem cell-derived 3D culture systems - it is now possible to re-create the architecture and physiology of human organs in remarkable detail. Human organoids provide unique opportunities for the study of human disease and complement animal models. Human organoids have been used to study infectious diseases, genetic disorders and cancers through the genetic engineering of human stem cells, as well as directly when organoids are generated from patient biopsy samples. This Review discusses the applications, advantages and disadvantages of human organoids as models of development and disease and outlines the challenges that have to be overcome for organoids to be able to substantially reduce the need for animal experiments.
In vitro three-dimensional (3D) cultures are emerging as novel systems with which to study tissue development, organogenesis and stem cell behavior ex vivo. When grown in a 3D environment, embryonic ...stem cells (ESCs) self-organize into organoids and acquire the right tissue patterning to develop into several endoderm- and ectoderm-derived tissues, mimicking their in vivo counterparts. Tissue-resident adult stem cells (AdSCs) also form organoids when grown in 3D and can be propagated in vitro for long periods of time. In this Review, we discuss recent advances in the generation of pluripotent stem cell- and AdSC-derived organoids, highlighting their potential for enhancing our understanding of human development. We will also explore how this new culture system allows disease modeling and gene repair for a personalized regenerative medicine approach.
Wnt/β‐catenin signaling is an ancient pathway that regulates key aspects of embryonic development, cell differentiation, proliferation, and adult stem cell homeostasis. Work from different ...laboratories has shed light on the molecular mechanisms underlying the Wnt pathway, including structural details of ligand–receptor interactions. One key aspect that has emerged from multiple studies is that endocytosis of the receptor complex plays a crucial role in fine‐tuning Wnt/β‐catenin signaling. Endocytosis is a key process involved in both activation as well as attenuation of Wnt signaling, but how this is regulated is still poorly understood. Importantly, recent findings show that Wnt also regulates central metabolic pathways such as the acquisition of nutrients through actin‐driven endocytic mechanisms. In this review, we propose that the Wnt pathway displays diverse characteristics that go beyond the regulation of gene expression, through a connection with the endocytic machinery.
In this review, we analyze the role that endocytosis plays in regulating Wnt signaling. We also discuss recent findings on how Wnt regulates metabolic processes, through endocytic mechanisms.
Gastric cancer ranks as the fifth most common human malignancy and the third leading cause of cancer related deaths. Depending on tumor stage, endoscopic or surgical resection supported by ...perioperative chemotherapy is the only curative option for patients. Due to late clinical manifestation and missing reliable biomarkers, early detection is challenging and overall survival remains poor. Organoids are cell aggregates cultured in three-dimensions that grow with similar characteristics as their tissue-of-origin. Due to their self-renewal and proliferative capacity, organoids can be maintained long term in culture and expanded in many cases in an unlimited fashion. Patient-derived organoid (PDO) libraries function as living biobanks, allowing the in depth analysis of tissue specific function, development and disease. The recent successful establishment of gastric cancer PDOs opens up new perspectives for multiple translational clinical applications. Here, we review different adult stem cell derived gastric organoid model systems and focus on their establishment, phenotypic and genotypic characterizations as well as their use in predicting therapy response.
The E3 ubiquitin ligases RING finger protein 43 (RNF43) and zinc and RING finger 3 (ZNRF3) have received great attention for their critical role in regulating WNT signalling during adult stem cell ...homeostasis. By promoting the turnover of WNT receptors, Frizzled and LRP5/6, RNF43 and ZNRF3 ensure that proper levels of WNT activity are maintained in stem cells. The molecular mechanism of RNF43/ZNRF3 activity is beginning to emerge from several recent studies, yet little is known about the regulation of RNF43/ZNRF3 at the post‐translational level. A study in this issue of EMBO Reports identifies the deubiquitinating enzyme USP42 as a key regulator of WNT signalling, which acts by antagonizing the ubiquitin‐dependent clearance of RNF43/ZNRF3 induced by R‐spondins (Giebel et al, 2021).
A study in this issue implicates the deubiquitinating enzyme USP42 in Wnt signalling. USP42 stabilizes RNF43/ZNRF3 at the cell surface, resulting in increased turnover of LRP6 and Frizzled and the inhibition of Wnt signalling.
Wnt signaling plays pivotal roles during our entire lives, from conception to death, through the regulation of morphogenesis in developing embryos and the maintenance of tissue homeostasis in adults. ...The regulation of Wnt signaling occurs on several levels: at the receptor level on the plasma membrane, at the β-catenin protein level in the cytoplasm, and through transcriptional regulation in the nucleus. Several recent studies have focused on the mechanisms of Wnt receptor regulation, following the discovery that the Wnt receptor frizzled (Fzd) is a target of the ubiquitin ligases, RNF43 and ZNRF3. RNF43 and ZNRF3 are homologous genes that are mutated in several cancers. The details underlying their mechanism of action continue to unfold, while at the same time raising many new questions. In this review, we discuss advances and controversies in our understanding of Wnt receptor regulation.
Three-dimensional organoids have been widely used for developmental and disease modeling. Organoids are derived from both adult and pluripotent stem cells. Various types are available for mimicking ...almost all major organs and tissues in the mouse and human. While culture protocols for stepwise differentiation and long-term expansion are well established, methods for genetic manipulation in organoids still need further standardization. In this review, we summarized different methods for organoid genetics and provide the pros and cons of each method for designing an optimal strategy.
Tissue regeneration is a multi-step process mediated by diverse cellular hierarchies and states that are also implicated in tissue dysfunction and pathogenesis. Here we leveraged single-cell RNA ...sequencing in combination with in vivo lineage tracing and organoid models to finely map the trajectories of alveolar-lineage cells during injury repair and lung regeneration. We identified a distinct AT2-lineage population, damage-associated transient progenitors (DATPs), that arises during alveolar regeneration. We found that interstitial macrophage-derived IL-1β primes a subset of AT2 cells expressing Il1r1 for conversion into DATPs via a HIF1α-mediated glycolysis pathway, which is required for mature AT1 cell differentiation. Importantly, chronic inflammation mediated by IL-1β prevents AT1 differentiation, leading to aberrant accumulation of DATPs and impaired alveolar regeneration. Together, this stepwise mapping to cell fate transitions shows how an inflammatory niche controls alveolar regeneration by controlling stem cell fate and behavior.
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•Injury-induced IL-1β signaling promotes differentiation of AT2 cells into AT1 cells•AT2 cells differentiate into AT1 cells via cell states of primed AT2 and DATPs•HIF1α signaling controls AT2-DAPT conversion and is essential for AT1 differentiation•Chronic inflammation impairs maturation of AT1 cells
Choi et al. show that inflammatory signals play a crucial role during alveolar regeneration after injury. They define stepwise differentiation trajectories for AT2 cells into AT1 cells via damage-associated transient progenitors (DATPs) and find that unresolved inflammation stalls transition of DATPs into mature AT1 cells.
Since the discovery of LGR5 as a marker of intestinal stem cells, the field has developed explosively and led to many new avenues of research. The inner workings of the intestinal crypt stem cell ...niche are now well understood. The study of stem cell–enriched genes has uncovered some previously unknown aspects of the Wnt signaling pathway, the major driver of crypt dynamics. LGR5+ stem cells can now be cultured over long periods in vitro as epithelial organoids or “mini-guts.” This technology opens new possibilities of using cultured adult stem cells for drug development, disease modeling, gene therapy, and regenerative medicine. This review describes the rediscovery of crypt base columnar cells as LGR5+ adult stem cells and summarizes subsequent progress, promises, unresolved issues, and challenges of the field.
Among the endodermal tissues of adult mammals, the gastrointestinal (GI) epithelium exhibits the highest turnover rate. As the ingested food moves along the GI tract, gastric acid, digestive enzymes, ...and gut resident microbes aid digestion as well as nutrient and mineral absorption. Due to the harsh luminal environment, replenishment of new epithelial cells is essential to maintain organ structure and function during routine turnover and injury repair. Tissue-specific adult stem cells in the GI tract serve as a continuous source for this immense regenerative activity. Tissue homeostasis is achieved by a delicate balance between gain and loss of cells. In homeostasis, temporal tissue damage is rapidly restored by well-balanced tissue regeneration, whereas prolonged imbalance may result in diverse pathologies of homeostasis and injury repair. Starting with a summary of the current knowledge of GI tract homeostasis, we continue with providing models of acute injury and chronic diseases. Finally, we will discuss how primary organoid cultures allow new insights into the mechanisms of homeostasis, injury repair, and disease, and how this novel 3D culture system has the potential to translate into the clinic.
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