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The small intestine is a specialised organ, essential for nutrient digestion and absorption. It is lined with a complex epithelial cell layer. Intestinal epithelial cells can be cultured in three-dimensional (3D) scaffolds as self-organising entities with distinct domains containing stem cells and differentiated cells. Recent developments in bioengineering provide new possibilities for directing the organisation of cells in vitro. In this Perspective, focusing on the small intestine, we discuss how studies at the interface between bioengineering and intestinal biology provide new insights into organ function. Specifically, we focus on engineered biomaterials, complex 3D structures resembling the intestinal architecture, and micro-physiological systems. Maria Antfolk and Kim Jensen discuss how to model intestinal epithelial cell function in the dish and how various physiologically important environmental conditions, for example, extracellular matrix, pressure and flow, can be modelled and how this is applicable to clinical work.

Intestinal organoids are fundamental in vitro tools that have enabled new research opportunities in intestinal stem cell research. Organoids can also be transplanted in vivo, which enables them to probe stem cell potential and be used for disease modeling and as a preclinical tool in regenerative medicine. Here we describe in detail how to orthotopically transplant epithelial organoids into the colon of recipient mice. In this assay, epithelial injury is initiated at the distal part of colon by the administration of dextran sulfate sodium, and organoids are infused into the luminal space via the anus. The infused organoids subsequently attach to the injured region and rebuild a donor-derived epithelium. The steps for cell infusion can be completed in 10 min. The assay has been applied successfully to organoids derived from both wild-type and genetically altered epithelial cells from adult colonic and small intestinal epithelium, as well as fetal small intestine. This is a versatile protocol, providing the technical basis for transplantation following alternative colonic injury models. It has been used previously for functional assays to probe cellular potential, and formed the basis for the first in-human clinical trial using colonic organoid transplantation therapy for intractable cases of ulcerative colitis. An approach to studying epithelia derived from organoids of either fetal or adult state and from both the small intestine and colon via transplantation into animals in which the colon has been damaged following administration of dextran sulfate sodium.

The sebaceous gland (SG) is an essential component of the skin, and SG dysfunction is debilitating 1 , 2 . Yet, the cellular bases for its origin, development and subsequent maintenance remain poorly understood. Here, we apply large-scale quantitative fate mapping to define the patterns of cell fate behaviour during SG development and maintenance. We show that the SG develops from a defined number of lineage-restricted progenitors that undergo a programme of independent and stochastic cell fate decisions. Following an expansion phase, equipotent progenitors transition into a phase of homeostatic turnover, which is correlated with changes in the mechanical properties of the stroma and spatial restrictions on gland size. Expression of the oncogene KrasG12D results in a release from these constraints and unbridled gland expansion. Quantitative clonal fate analysis reveals that, during this phase, the primary effect of the Kras oncogene is to drive a constant fate bias with little effect on cell division rates. These findings provide insight into the developmental programme of the SG, as well as the mechanisms that drive tumour progression and gland dysfunction. Andersen, Hannezo, Ulyanchenko et al. map cell behaviour and spatiotemporal dynamics of the sebaceous gland during homeostasis and oncogene-induced gland expansion, and show that all basal cells contribute to long-term gland maintenance.

A cross-sectional survey to evaluate the current management of wet age-related macular degeneration (wAMD) and to identify barriers to treatment from a patient and caregiver perspective. An ophthalmologist-devised questionnaire was given to a global cohort of patients who were receiving (or had previously received) antivascular endothelial growth factor injections and to caregivers (paid and unpaid) to evaluate the impact of wAMD on their lives. Responders included 910 patients and 890 caregivers; wAMD was diagnosed in both eyes in 45% of patients, and 64% had been receiving injections for > 1 year. Many caregivers were a child/grandchild (47%) or partner (23%) of the patient; only 7% were professional caregivers. Most (73%) patients visited a health care professional within 1 month of experiencing vision changes and 54% began treatment immediately. Most patients and caregivers reported a number of obstacles in managing wAMD, including the treatment itself (35% and 39%, respectively). Sixteen percent of patients also missed a clinic visit. Most patients seek medical assistance promptly for a change in vision; however, about a quarter of them do not. This highlights a lack of awareness surrounding eye health and the impact of a delayed diagnosis. Most patients and caregivers identified a number of obstacles in managing wAMD.

Adult intestinal stem cells are located at the bottom of crypts of Lieberkühn, where they express markers such as LGR5 1 , 2 and fuel the constant replenishment of the intestinal epithelium 1 . Although fetal LGR5-expressing cells can give rise to adult intestinal stem cells 3 , 4 , it remains unclear whether this population in the patterned epithelium represents unique intestinal stem-cell precursors. Here we show, using unbiased quantitative lineage-tracing approaches, biophysical modelling and intestinal transplantation, that all cells of the mouse intestinal epithelium—irrespective of their location and pattern of LGR5 expression in the fetal gut tube—contribute actively to the adult intestinal stem cell pool. Using 3D imaging, we find that during fetal development the villus undergoes gross remodelling and fission. This brings epithelial cells from the non-proliferative villus into the proliferative intervillus region, which enables them to contribute to the adult stem-cell niche. Our results demonstrate that large-scale remodelling of the intestinal wall and cell-fate specification are closely linked. Moreover, these findings provide a direct link between the observed plasticity and cellular reprogramming of differentiating cells in adult tissues following damage 5 – 9 , revealing that stem-cell identity is an induced rather than a hardwired property. Lineage tracing, biophysical modelling and intestinal transplantation approaches are used to demonstrate that, in the mouse fetal intestinal epithelium, cells are highly plastic with respect to cellular identity and, independent of LGR5 expression and cell position, can contribute to the adult stem cell compartment.

Organs are anatomically compartmentalised to cater for specialised functions. In the small intestine (SI), regionalisation enables sequential processing of food and nutrient absorption. While several studies indicate the critical importance of non-epithelial cells during development and homeostasis, the extent to which these cells contribute to regionalisation during morphogenesis remains unexplored. Here, we identify a mesenchymal-epithelial crosstalk that shapes the developing SI during late morphogenesis. We find that subepithelial mesenchymal cells are characterised by gradients of factors supporting Wnt signalling and stimulate epithelial growth in vitro. Such a gradient impacts epithelial gene expression and regional villus formation along the anterior-posterior axis of the SI. Notably, we further provide evidence that Wnt signalling directly regulates epithelial expression of Sonic Hedgehog (SHH), which, in turn, acts on mesenchymal cells to drive villi formation. Taken together our results uncover a mechanistic link between Wnt and Hedgehog signalling across different cellular compartments that is central for anterior-posterior regionalisation and correct formation of the SI. The small intestine forms via crosstalk between epithelial and mesenchymal cell compartments. Here, the authors show that a gradient of Wnt signalling along the anterior-posterior axis regulates Sonic Hedgehog which is required for correct formation and regionalization of the small intestine.

Considerable progress has been made in characterizing epidermal stem cells by microarray analysis of FACS-selected populations. One limitation of this approach is that the gene expression profiles represent the average of the cell population, potentially masking cellular heterogeneity of functional significance. To overcome this problem, we have performed single-cell expression profiling. We have generated cDNA libraries from single human epidermal cells, designated as stem or transit-amplifying cells on the basis of Deltal and melanoma-associated chondroitin sulfate proteoglycan expression. Of the 14 putative stem cell markers identified, we selected one, the EGF receptor antagonist leucine-rich repeats and immunoglobulin-like domains 1 (Lrigl), for further study. Lrigl was expressed in groups of basal cells in human interfollicular epidermis previously identified as enriched for stem cells. Overexpression of Lrigl decreased keratinocyte proliferation but did not affect the proportion of stem and transit-amplifying cells, as judged by clonal growth characteristics. Down-regulation of Lrigl using siRNA increased cell-surface EGF receptor levels, enhanced activation of downstream pathways, and stimulated proliferation. Lrigl acted in part by negatively regulating the Myc promoter. We propose that Lrigl maintains epidermal stem cells in a quiescent nondividing state, and that Lrigl down-regulation triggers proliferation.

In this protocol, we describe how to isolate keratinocytes from adult mouse epidermis, fractionate them into different sub-populations on the basis of cell surface markers and examine their function in an in vivo skin reconstitution assay with disaggregated neonatal dermal cells. We also describe how the isolated keratinocytes can be subjected to clonal analysis in vitro and in vivo and how to enrich for hair follicle-inducing dermal papilla cells in the dermal preparation. Using these approaches, it is possible to compare the capacity of different populations of adult epidermal stem cells to proliferate and to generate progeny that differentiate along the different epidermal lineages. Isolating, fractionating and grafting cells for the skin reconstitution assay is normally spread over 2 d. Clonal growth in culture is assessed after 14 d, while evaluation of the grafts is carried out after 4–5 weeks.

Epithelial cells rapidly adapt their behaviour in response to increasing tissue demands. However, the processes that finely control these cell decisions remain largely unknown. The postnatal period covering the transition between early tissue expansion and the establishment of adult homeostasis provides a convenient model with which to explore this question. Here, we demonstrate that the onset of homeostasis in the epithelium of the mouse oesophagus is guided by the progressive build-up of mechanical strain at the organ level. Single-cell RNA sequencing and whole-organ stretching experiments revealed that the mechanical stress experienced by the growing oesophagus triggers the emergence of a bright Krüppel-like factor 4 (KLF4) committed basal population, which balances cell proliferation and marks the transition towards homeostasis in a yes-associated protein (YAP)-dependent manner. Our results point to a simple mechanism whereby mechanical changes experienced at the whole-tissue level are integrated with those sensed at the cellular level to control epithelial cell fate. McGinn et al. show that mechanical stretch in the developing oesophagus promotes the YAP-dependent emergence of a KLF4 + committed basal cell population, revealing how physiological strain triggers the transition to adult homeostasis.

Aims: Health policy decisions should be based on national social preferences. In the absence of a set of Danish health preferences, patient outcome studies using the EQ-5D instrument have typically used UK health state valuations. This article describes the development of a Danish EQ-5D value set. Methods: Regression modelling was based on Time Trade-Off (TTO) data derived from computer-assisted interviews conducted with 1,332 respondents from the Danish general population. Using a split-sample technique, 46 health states were directly valued by the respondents. Five different model types were tested and compared on statistical and theoretical grounds. Eleven different specifications were then tested for the chosen model type to identify the most appropriate model that had high explanatory power and parameters that were both consistent (positively signed) and statistically significant. Results: An additive random effects model was found to be superior to ordinary least squares, fixed effects, random coefficient and censored Tobit modelling approaches. From the 11 model specifications tested, the TTO3 model (main effects model, without an N3 factor) performed best and was used to generate a Danish set of health state preferences. Conclusions: An additive random effects model appears to adequately generate a Danish set of EQ-5D health state preferences. The model has high explanatory power and produces consistent and significant parameters for EQ-5D dimensions and levels. It is recommended that this value set be used in Danish cost-utility studies using EQ-5D.