A hierarchical Bayesian model for understanding the spatiotemporal dynamics of the intestinal epithelium

Our work addresses two key challenges, one biological and one methodological. First, we aim to understand how proliferation and cell migration rates in the intestinal epithelium are related under healthy, damaged (Ara-C treated) and recovering conditions, and how these relations can be used to identify mechanisms of repair and regeneration. We analyse new data, presented in more detail in a companion paper, in which BrdU/IdU cell-labelling experiments were performed under these respective conditions. Second, in considering how to more rigorously process these data and interpret them using mathematical models, we use a probabilistic, hierarchical approach. This provides a best-practice approach for systematically modelling and understanding the uncertainties that can otherwise undermine the generation of reliable conclusions-uncertainties in experimental measurement and treatment, difficult-to-compare mathematical models of underlying mechanisms, and unknown or unobserved parameters. Both spatially discrete and continuous mechanistic models are considered and related via hierarchical conditional probability assumptions. We perform model checks on both in-sample and out-of-sample datasets and use them to show how to test possible model improvements and assess the robustness of our conclusions. We conclude, for the present set of experiments, that a primarily proliferation-driven model suffices to predict labelled cell dynamics over most time-scales

Colorectal Cancer Through Simulation and Experiment

Colorectal cancer has continued to generate a huge amount of research interest over several decades, forming a canonical example of tumourigenesis since its use in Fearon and Vogelstein’s linear model of genetic mutation. Over time, the field has witnessed a transition from solely experimental work to the inclusion of mathematical biology and computer-based modelling. The fusion of these disciplines has the potential to provide valuable insights into oncologic processes, but also presents the challenge of uniting many diverse perspectives. Furthermore, the cancer cell phenotype defined by the ‘Hallmarks of Cancer’ has been extended in recent times and provides an excellent basis for future research. We present a timely summary of the literature relating to colorectal cancer, addressing the traditional experimental findings, summarising the key mathematical and computational approaches, and emphasising the role of the Hallmarks in current and future developments. We conclude with a discussion of interdisciplinary work, outlining areas of experimental interest which would benefit from the insight that mathematical and computational modelling can provide

Approaches to in vitro tissue regeneration with application for human disease modeling and drug development

Reliable in vitro human disease models that capture the complexity of in vivo tissue behaviors are crucial to gain mechanistic insights into human disease and enable the development of treatments that are effective across broad patient populations. The integration of stem cell technologies, tissue engineering, emerging biomaterials strategies and microfabrication processes, as well as computational and systems biology approaches, is enabling new tools to generate reliable in vitro systems to study the molecular basis of human disease and facilitate drug development. In this review, we discuss these recently developed tools and emphasize opportunities and challenges involved in combining these technologies toward regenerative science.National Institute for Biomedical Imaging and Bioengineering (U.S.) (Grant 5R01EB010246-02)National Center for Advancing Translational Sciences (U.S.) (Grant 1UH2TR000496)United States. Defense Advanced Research Projects Agency (Cooperative Agreement W911NF-12-2-0039

Exploring the regeneration potential of salivary glands using organoids as a model

Radiotherapy is a potential life-saving treatment for head and neck cancer patients. However, despite improvements in precision of radiation dose delivered, the unavoidable co-irradiation of salivary gland still leads to irreversible diminishing of saliva secretion affecting among others the ability to speak, eat and sleep, drastically decreasing the quality of life of the patients. Existing treatments for this dry mouth syndrome, only provide short-term relief. Therefore, the development of new therapies, such as stem cell therapy, is crucial to alleviate this side effect caused by irradiation. Combining mouse injury models with 3D organoid cultures of mouse and human salivary gland derived cells, it is attempted to identify the optimal cell source for, as well as the regulatory mechanisms involved in, the salivary gland regeneration process. Thereby this work focused on the development and optimization of a potentially clinically relevant regenerative therapy approach to functionally restore the irradiated salivary gland tissue

The role of space in homeostasis and preneoplasia in stratified squamous epithelia

A major subject of study in biological research is the dynamics of stem cells in squamous epithelia. Given that most common human cancers develop from epithelia, understanding the rules of cell fate decision in these systems is key to explaining not only healthy tissue growth and maintenance but also the processes of mutagenesis and cancer. The aim of my project was to investigate the dynamics in squamous epithelial tissues both in homeostasis and preneoplasia, using cellular automata (CA) models. Stem cell dynamics has been shown to be accurately described by a simple mathematical model, the single progenitor (SP) model. Reliable parameterisation of this model would give access to valuable quantitative information on epithelial tissue maintenance and enable investigating how mutations affect tissue dynamics. I initially identified the most appropriate method for accurately parameterising the homeostatic system. I then sought to account for the spatial patterning of cells by implementing the SP model in two-dimensional space. The spatial model was able to reproduce the key signatures of homeostatic dynamics, thus showing that restrictions imposed by tissue organization do not alter the neutral dynamics. Furthermore, I studied non-homeostatic dynamics in stratified squamous epithelial tissues by spatially modelling the growth and competition of non-neutral mutations as well as the effects of wounding in the tissue. The studied dynamics of Notch and p53 mutant clones in mouse epithelia has been found to be highly distinct, with the former fully colonizing the tissue whereas the latter only partially. I demonstrated that the two mutants’ tissue takeover dynamics can be recapitulated by two distinct spatial feedback rules, on the basis of response to crowding, providing a mechanistic explanation of the observed distinct growth modes. Finally, mutant competition was explored. A striking effect resulting from the spatial interaction of the two mutations in a wild-type background is that the p53 mutant cell population was always outcompeted by the Notch mutant population and appeared to shrink. Considering this consistent emergent behaviour in the competition simulations and given the paucity of Notch mutations in human cancer datasets, it is tempting to speculate that the aggressive fitness of Notch may offer a tumour-protective effect

Chronic TNFα-driven injury delays cell migration to villi in the intestinal epithelium

The intestinal epithelium is a single layer of cells which provides the first line of defence of the intestinal mucosa to bacterial infection. Cohesion of this physical barrier is supported by renewal of epithelial stem cells, residing in invaginations called crypts, and by crypt cell migration onto protrusions called villi; dysregulation of such mechanisms may render the gut susceptible to chronic inflammation. The impact that excessive or misplaced epithelial cell death may have on villus cell migration is currently unknown. We integrated cell-tracking methods with computational models to determine how epithelial homeostasis is affected by acute and chronic TNFα-driven epithelial cell death. Parameter inference reveals that acute inflammatory cell death has a transient effect on epithelial cell dynamics, whereas cell death caused by chronic elevated TNFα causes a delay in the accumulation of labelled cells onto the villus compared to the control. Such a delay may be reproduced by using a cell-based model to simulate the dynamics of each cell in a crypt-villus geometry, showing that a prolonged increase in cell death slows the migration of cells from the crypt to the villus. This investigation highlights which injuries (acute or chronic) may be regenerated and which cause disruption of healthy epithelial homeostasis

Simulation and inference algorithms for stochastic biochemical reaction networks: from basic concepts to state-of-the-art

Stochasticity is a key characteristic of intracellular processes such as gene regulation and chemical signalling. Therefore, characterising stochastic effects in biochemical systems is essential to understand the complex dynamics of living things. Mathematical idealisations of biochemically reacting systems must be able to capture stochastic phenomena. While robust theory exists to describe such stochastic models, the computational challenges in exploring these models can be a significant burden in practice since realistic models are analytically intractable. Determining the expected behaviour and variability of a stochastic biochemical reaction network requires many probabilistic simulations of its evolution. Using a biochemical reaction network model to assist in the interpretation of time course data from a biological experiment is an even greater challenge due to the intractability of the likelihood function for determining observation probabilities. These computational challenges have been subjects of active research for over four decades. In this review, we present an accessible discussion of the major historical developments and state-of-the-art computational techniques relevant to simulation and inference problems for stochastic biochemical reaction network models. Detailed algorithms for particularly important methods are described and complemented with MATLAB implementations. As a result, this review provides a practical and accessible introduction to computational methods for stochastic models within the life sciences community

Deciphering the spatiotemporal dynamics of intestinal aging in vertebrates using the African turquoise killifish

Aging is the major risk factor for many top-killing diseases and represents a problem for both the individual and the society. How the aging process is influenced and causally connected to microbiota is an emerging research area, with far-reaching findings obtained within the past few years. However, major underlying connections still remain elusive, in part hindered by a lack of suitable experimental model systems. The turquoise killifish is an ideal model to fill this gap and study microbiota in the context of aging, as it uniquely combines a very short lifespan with vertebrate features, such as a complex gut microbiota. However, knowledge about the killifish intestinal characteristics and gut microbiota is largely absent. Important key aspects I address include a detailed definition of aging dynamics, a characterization of gut compartmentalization and sex-specific intestinal traits, as well as the question whether non-invasive stool samples could be experimentally utilized for assessment of gut microbiota features. I thus set out to characterize killifish spatiotemporal aging dynamics and sex-specific intestinal microbial and molecular patterns by performing multi-omics analyses on intestinal sections of young and old, male and female killifish. I found strong evidence for a compartmentalization of the killifish intestine on a molecular and morphological level, with specific functions that can also be found in the mammalian intestine. Surprisingly, I did not observe section-specific microbial communities in contrast to findings from other animals including fish. I detected compelling evidence for extracellular matrix restructuring in the aged killifish intestine, with an accumulation of collagen and an increase in muscle thickness, possibly impeding the intestinal function in old fish. For the first time, I showed that the killifish intestine exhibits sex-specific molecular traits, especially concerning the coagulation process. Moreover, I asked whether non-invasive stool samples can be used as a proxy for gut microbiota by collecting microbiota samples of stool, intestinal and food samples. In addition, I set out to explore whether stool samples can be utilized to build models predicting fish age or remaining life by conducting a longitudinal collection of individual stool samples along killifish life. Excitingly, I discovered shared microbial features between stool and gut microbiota and showed for the first time that a series of stool microbial samples in combination with a machine learning approach allows prediction of both age and lifespan. My studies not only set the ground for future research on killifish gut microbiota, but provide novel promising results highlighting the importance of gut microbiota research in the context of aging

Cells of the human intestinal tract mapped across space and time

Acknowledgements We acknowledge support from the Wellcome Sanger Cytometry Core Facility, Cellular Genetics Informatics team, Cellular Generation and Phenotyping (CGaP) and Core DNA Pipelines. This work was financially supported by the Wellcome Trust (W1T20694, S.A.T.; 203151/Z/16/Z, R. A. Barker.); the European Research Council (646794, ThDefine, S.A.T.); an MRC New Investigator Research Grant (MR/T001917/1, M.Z.); and a project grant from the Great Ormond Street Hospital Children’s Charity, Sparks (V4519, M.Z.). The human embryonic and fetal material was provided by the Joint MRC/Wellcome (MR/R006237/1) Human Developmental Biology Resource (https://www.hdbr.org/). K.R.J. holds a Non-Stipendiary Junior Research Fellowship from Christ’s College, University of Cambridge. M.R.C. is supported by a Medical Research Council Human Cell Atlas Research Grant (MR/S035842/1) and a Wellcome Trust Investigator Award (220268/Z/20/Z). H.W.K. is funded by a Sir Henry Wellcome Fellowship (213555/Z/18/Z). A.F. is funded by a Wellcome PhD Studentship (102163/B/13/Z). K.T.M. is funded by an award from the Chan Zuckerberg Initiative. H.H.U. is supported by the Oxford Biomedical Research Centre (BRC) and the The Leona M. and Harry B. Helmsley Charitable Trust. We thank A. Chakravarti and S. Chatterjee for their contribution to the analysis of the enteric nervous system. We also thank R. Lindeboom and C. Talavera-Lopez for support with epithelium and Visium analysis, respectively; C. Tudor, T. Li and O. Tarkowska for image processing and infrastructure support; A. Wilbrey-Clark and T. Porter for support with Visium library preparation; A. Ross and J. Park for access to and handling of fetal tissue; A. Hunter for assistance in protocol development; D. Fitzpatrick for discussion on developmental intestinal disorders; and J. Eliasova for the graphical images. We thank the tissue donors and their families, and the Cambridge Biorepository for Translational Medicine and Human Developmental Biology Resource, for access to human tissue. This publication is part of the Human Cell Atlas: https://www.humancellatlas.org/publications.Peer reviewedPublisher PD

Cells of the human intestinal tract mapped across space and time

The cellular landscape of the human intestinal tract is dynamic throughout life, developing in utero and changing in response to functional requirements and environmental exposures. Here, to comprehensively map cell lineages, we use single-cell RNA sequencing and antigen receptor analysis of almost half a million cells from up to 5 anatomical regions in the developing and up to 11 distinct anatomical regions in the healthy paediatric and adult human gut. This reveals the existence of transcriptionally distinct BEST4 epithelial cells throughout the human intestinal tract. Furthermore, we implicate IgG sensing as a function of intestinal tuft cells. We describe neural cell populations in the developing enteric nervous system, and predict cell-type-specific expression of genes associated with Hirschsprung’s disease. Finally, using a systems approach, we identify key cell players that drive the formation of secondary lymphoid tissue in early human development. We show that these programs are adopted in inflammatory bowel disease to recruit and retain immune cells at the site of inflammation. This catalogue of intestinal cells will provide new insights into cellular programs in development, homeostasis and disease