HNF4 factors control chromatin accessibility and are redundantly required for maturation of the fetal intestine

Intestinal epigenomic alterations are associated with a dysregulated nutrient absorption phenotype in obesity

Obesity is an epidemic with myriad health effects, but little is understood regarding individual obese phenotypes and how they may respond to therapy. Epigenetic changes associated with obesity have been detected in blood, liver, pancreas, and adipose tissues. Previous work found that dietary glucose hyperabsorption occurs in some obese subjects, but detailed transcriptional or epigenomic features of the intestine associated with this phenotype are unknown. This study evaluated differentially expressed genes and relative chromatin accessibility in intestinal organoids established from donors classified as lean, obese, or obese hyperabsorptive by body mass index and glucose transport assays. Transcriptomic analysis indicated that obese hyperabsorptive subjects have significantly upregulated dietary nutrient absorption proteins and downregulated type I interferon targets. Chromatin accessibility and transcription factor footprinting suggested that enhanced binding of HNF4G promotes the obese hyperabsorption phenotype. Quantitative PCR assessment in a larger subject cohort suggested that intestinal epithelial expression of CUBN, GIP, and SLC2A5 have high correlation with hyperabsorption. The obese hyperabsorption phenotype is characterized by transcriptional changes that support increased nutrient uptake and may be driven by differentially accessible chromatin. Recognizing unique intestinal phenotypes in obesity provides new perspective in considering therapeutic targets and options to manage the disease.

Metastasis of colon cancer requires Dickkopf-2 to generate cancer cells with Paneth cell properties

Metastasis is the leading cause of cancer-related mortality. Paneth cells provide stem cell niche factors in homeostatic conditions, but the underlying mechanisms of cancer stem cell niche development are unclear. Here we report that Dickkopf-2 (DKK2) is essential for the generation of cancer cells with Paneth cell properties during colon cancer metastasis. Splenic injection of Dkk2-knockout (KO) cancer organoids into C57BL/6 mice resulted in a significant reduction of liver metastases. Transcriptome analysis showed reduction of Paneth cell markers such as lysozymes in KO organoids. Single cell RNA sequencing analyses of murine metastasized colon cancer cells and patient samples identified the presence of lysozyme positive cells with Paneth cell properties including enhanced glycolysis. Further analyses of transcriptome and chromatin accessibility suggested Hepatocyte nuclear factor 4-alpha (HNF4A) as a downstream target of DKK2. Chromatin immunoprecipitation followed by sequencing analysis revealed that HNF4A binds to the promoter region of Sox9, a well-known transcription factor for Paneth cell differentiation. In the liver metastatic foci, DKK2 knockout rescued HNF4A protein levels followed by reduction of lysozyme positive cancer cells. Taken together, DKK2-mediated reduction of HNF4A protein promotes the generation of lysozyme positive cancer cells with Paneth cell properties in the metastasized colon cancers.

A Mutation-driven oncofetal regression fuels phenotypic plasticity in colorectal cancer

Targeting cancer stem cells (CSCs) is crucial for effective cancer treatment 1 . However, the molecular mechanisms underlying resistance to LGR5 + CSCs depletion in colorectal cancer (CRC) 2,3 remain largely elusive. Here, we unveil the existence of a primitive cell state dubbed the oncofetal (OnF) state, which works in tandem with the LGR5 + stem cells (SCs) to fuel tumor evolution in CRC. OnF cells emerge early during intestinal tumorigenesis and exhibit features of lineage plasticity. Normally suppressed by the Retinoid X Receptor (RXR) in mature SCs, the OnF program is triggered by genetic deletion of the gatekeeper APC. We demonstrate that diminished RXR activity unlocks an epigenetic circuity governed by the cooperative action of YAP and AP1, leading to OnF reprogramming. This high-plasticity state is inherently resistant to conventional chemotherapies and its adoption by LGR5 + CSCs enables them to enter a drug-tolerant state. Furthermore, through phenotypic tracing and ablation experiments, we uncover a functional redundancy between the OnF and stem cell (SC) states and show that targeting both cellular states is essential for sustained tumor regression in vivo . Collectively, these findings establish a mechanistic foundation for developing effective combination therapies with enduring impact on CRC treatment.

Multiple roles and regulatory mechanisms of the transcription factor HNF4 in the intestine

Hepatocyte nuclear factor 4-alpha (HNF4α) drives a complex array of transcriptional programs across multiple organs. Beyond its previously documented function in the liver, HNF4α has crucial roles in the kidney, intestine, and pancreas. In the intestine, a multitude of functions have been attributed to HNF4 and its accessory transcription factors, including but not limited to, intestinal maturation, differentiation, regeneration, and stem cell renewal. Functional redundancy between HNF4α and its intestine-restricted paralog HNF4γ, and co-regulation with other transcription factors drive these functions. Dysregulated expression of HNF4 results in a wide range of disease manifestations, including the development of a chronic inflammatory state in the intestine. In this review, we focus on the multiple molecular mechanisms of HNF4 in the intestine and explore translational opportunities. We aim to introduce new perspectives in understanding intestinal genetics and the complexity of gastrointestinal disorders through the lens of HNF4 transcription factors.

Mammalian Intestinal Development and Differentiation-The State of the Art

The development of the mammalian intestine, from its earliest origins as a morphologically uniform sheet of endoderm cells during gastrulation into the complex organ system that is essential for the life of the organism, is a truly fascinating process. During midgestation development, reciprocal interactions between endoderm-derived epithelium and mesoderm-derived mesenchyme enable villification, or the conversion of a radially symmetric pseudostratified epithelium into the functional subdivision of crypts and villi. Once a mature crypt-villus axis is established, proliferation and differentiation of new epithelial cells continue throughout life. Spatially localized signals including the wingless and Int-1, fibroblast growth factor, and Hippo systems, among others, ensure that new cells are being born continuously in the crypt. As cells exit the crypt compartment, a gradient of bone morphogenetic protein signaling limits proliferation to allow for the specification of multiple mature cell types. The first major differentiation decision is dependent on Notch signaling, which specifies epithelial cells into absorptive and secretory lineages. The secretory lineage is subdivided further into Paneth, goblet, tuft, and enteroendocrine cells via a complex network of transcription factors. Although some of the signaling molecules are produced by epithelial cells, critical components are derived from specialized crypt-adjacent mesenchymal cells termed telocytes, which are marked by Forkhead box l1, GLI Family Zinc Finger 1, and platelet-derived growth factor receptor α. The crucial nature of these processes is evidenced by the multitude of intestinal disorders such as colorectal cancer, short-bowel syndrome, and inflammatory bowel disease, which all reflect perturbations of the development and/or differentiation of the intestine.

Transcriptional and epigenomic profiling identifies YAP signaling as a key regulator of intestinal epithelium maturation

During intestinal organogenesis, equipotent epithelial progenitors mature into phenotypically distinct stem cells that are responsible for lifelong maintenance of the tissue. While the morphological changes associated with the transition are well characterized, the molecular mechanisms underpinning the maturation process are not fully understood. Here, we leverage intestinal organoid cultures to profile transcriptional, chromatin accessibility, DNA methylation, and three-dimensional (3D) chromatin conformation landscapes in fetal and adult epithelial cells. We observed prominent differences in gene expression and enhancer activity, which are accompanied by local changes in 3D organization, DNA accessibility, and methylation between the two cellular states. Using integrative analyses, we identified sustained Yes-Associated Protein (YAP) transcriptional activity as a major gatekeeper of the immature fetal state. We found the YAP-associated transcriptional network to be regulated at various levels of chromatin organization and likely to be coordinated by changes in extracellular matrix composition. Together, our work highlights the value of unbiased profiling of regulatory landscapes for the identification of key mechanisms underlying tissue maturation.

An organoid-based CRISPR-Cas9 screen for regulators of intestinal epithelial maturation and cell fate

Generation of functionally mature organs requires exquisite control of transcriptional programs governing cell state transitions during development. Despite advances in understanding the behavior of adult intestinal stem cells and their progeny, the transcriptional regulators that control the emergence of the mature intestinal phenotype remain largely unknown. Using mouse fetal and adult small intestinal organoids, we uncover transcriptional differences between the fetal and adult state and identify rare adult-like cells present in fetal organoids. This suggests that fetal organoids have an inherent potential to mature, which is locked by a regulatory program. By implementing a CRISPR-Cas9 screen targeting transcriptional regulators expressed in fetal organoids, we establish Smarca4 and Smarcc1 as important factors safeguarding the immature progenitor state. Our approach demonstrates the utility of organoid models in the identification of factors regulating cell fate and state transitions during tissue maturation and reveals that SMARCA4 and SMARCC1 prevent precocious differentiation during intestinal development.

ONECUT2 regulates RANKL-dependent enterocyte and microfold cell differentiation in the small intestine; a multi-omics study

Microfold (M) cells reside in the intestinal epithelium of Peyer's patches (PP). Their unique ability to take up and transport antigens from the intestinal lumen to the underlying lymphoid tissue is key in the regulation of the gut-associated immune response. Here, we applied a multi-omics approach to investigate the molecular mechanisms that drive M cell differentiation in mouse small intestinal organoids. We generated a comprehensive profile of chromatin accessibility changes and transcription factor dynamics during in vitro M cell differentiation, allowing us to uncover numerous cell type-specific regulatory elements and associated transcription factors. By using single-cell RNA sequencing, we identified an enterocyte and M cell precursor population. We used our newly developed computational tool SCEPIA to link precursor cell-specific gene expression to transcription factor motif activity in cis-regulatory elements, uncovering high expression of and motif activity for the transcription factor ONECUT2. Subsequent in vitro and in vivo perturbation experiments revealed that ONECUT2 acts downstream of the RANK/RANKL signalling axis to support enterocyte differentiation, thereby restricting M cell lineage specification. This study sheds new light on the mechanism regulating cell fate balance in the PP, and it provides a powerful blueprint for investigation of cell fate switches in the intestinal epithelium.

Maf family transcription factors are required for nutrient uptake in the mouse neonatal gut

There are fundamental differences in how neonatal and adult intestines absorb nutrients. In adults, macromolecules are broken down into simpler molecular components in the lumen of the small intestine, then absorbed. In contrast, neonates are thought to rely on internalization of whole macromolecules and subsequent degradation in the lysosome. Here, we identify the Maf family transcription factors MAFB and c-MAF as markers of terminally differentiated intestinal enterocytes throughout life. The expression of these factors is regulated by HNF4α and HNF4γ, master regulators of enterocyte cell fate. Loss of Maf factors results in a neonatal-specific failure to thrive and loss of macromolecular nutrient uptake. RNA-Seq and CUT&RUN analyses defined an endo-lysosomal program as being downstream of these transcription factors. We demonstrate major transcriptional changes in metabolic pathways, including fatty acid oxidation and increases in peroxisome number, in response to loss of Maf proteins. Finally, we show that loss of BLIMP1, a repressor of adult enterocyte genes, shows highly overlapping changes in gene expression and similar defects in macromolecular uptake. This work defines transcriptional regulators that are necessary for nutrient uptake in neonatal enterocytes.

Conserved roles for Hnf4 family transcription factors in zebrafish development and intestinal function

Transcription factors play important roles in the development of the intestinal epithelium and its ability to respond to endocrine, nutritional, and microbial signals. Hepatocyte nuclear factor 4 family nuclear receptors are liganded transcription factors that are critical for the development and function of multiple digestive organs in vertebrates, including the intestinal epithelium. Zebrafish have 3 hepatocyte nuclear factor 4 homologs, of which, hnf4a was previously shown to mediate intestinal responses to microbiota in zebrafish larvae. To discern the functions of other hepatocyte nuclear factor 4 family members in zebrafish development and intestinal function, we created and characterized mutations in hnf4g and hnf4b. We addressed the possibility of genetic redundancy amongst these factors by creating double and triple mutants which showed different rates of survival, including apparent early lethality in hnf4a; hnf4b double mutants and triple mutants. RNA sequencing performed on digestive tracts from single and double mutant larvae revealed extensive changes in intestinal gene expression in hnf4a mutants that were amplified in hnf4a; hnf4g mutants, but limited in hnf4g mutants. Changes in hnf4a and hnf4a; hnf4g mutants were reminiscent of those seen in mice including decreased expression of genes involved in intestinal function and increased expression of cell proliferation genes, and were validated using transgenic reporters and EdU labeling in the intestinal epithelium. Gnotobiotics combined with RNA sequencing also showed hnf4g has subtler roles than hnf4a in host responses to microbiota. Overall, phenotypic changes in hnf4a single mutants were strongly enhanced in hnf4a; hnf4g double mutants, suggesting a conserved partial genetic redundancy between hnf4a and hnf4g in the vertebrate intestine.

Principles of human and mouse nephron development

The mechanisms underlying kidney development in mice and humans is an area of intense study. Insights into kidney organogenesis have the potential to guide our understanding of the origin of congenital anomalies and enable the assembly of genetic diagnostic tools. A number of studies have delineated signalling nodes that regulate positional identities and cell fates of nephron progenitor and precursor cells, whereas cross-species comparisons have markedly enhanced our understanding of conserved and divergent features of mammalian kidney organogenesis. Greater insights into the complex cellular movements that occur as the proximal-distal axis is established have challenged our understanding of nephron patterning and provided important clues to the elaborate developmental context in which human kidney diseases can arise. Studies of kidney development in vivo have also facilitated efforts to recapitulate nephrogenesis in kidney organoids in vitro, by providing a detailed blueprint of signalling events, cell movements and patterning mechanisms that are required for the formation of correctly patterned nephrons and maturation of physiologically functional apparatus that are responsible for maintaining human health.

DNA methylation dynamics and dysregulation delineated by high-throughput profiling in the mouse

We have developed a mouse DNA methylation array that contains 296,070 probes representing the diversity of mouse DNA methylation biology. We present a mouse methylation atlas as a rich reference resource of 1,239 DNA samples encompassing distinct tissues, strains, ages, sexes, and pathologies. We describe applications for comparative epigenomics, genomic imprinting, epigenetic inhibitors, patient-derived xenograft assessment, backcross tracing, and epigenetic clocks. We dissect DNA methylation processes associated with differentiation, aging, and tumorigenesis. Notably, we find that tissue-specific methylation signatures localize to binding sites for transcription factors controlling the corresponding tissue development. Age-associated hypermethylation is enriched at regions of Polycomb repression, while hypomethylation is enhanced at regions bound by cohesin complex members. Apc ^Min/+ polyp-associated hypermethylation affects enhancers regulating intestinal differentiation, while hypomethylation targets AP-1 binding sites. This Infinium Mouse Methylation BeadChip (version MM285) is widely accessible to the research community and will accelerate high-sample-throughput studies in this important model organism.

Single-cell chromatin profiling of the primitive gut tube reveals regulatory dynamics underlying lineage fate decisions

Development of the gastrointestinal system occurs after gut tube closure, guided by spatial and temporal control of gene expression. However, it remains unclear what forces regulate these spatiotemporal gene expression patterns. Here we perform single-cell chromatin profiling of the primitive gut tube to reveal organ-specific chromatin patterns that reflect the anatomical patterns of distinct organs. We generate a comprehensive map of epigenomic changes throughout gut development, demonstrating that dynamic chromatin accessibility patterns associate with lineage-specific transcription factor binding events to regulate organ-specific gene expression. Additionally, we show that loss of Sox2 and Cdx2, foregut and hindgut lineage-specific transcription factors, respectively, leads to fate shifts in epigenomic patterns, linking transcription factor binding, chromatin accessibility, and lineage fate decisions in gut development. Notably, abnormal expression of Sox2 in the pancreas and intestine impairs lineage fate decisions in both development and adult homeostasis. Together, our findings define the chromatin and transcriptional mechanisms of organ identity and lineage plasticity in development and adult homeostasis.

The primitive gut tube gives rise to all major internal organs, while underlying regulatory mechanisms are unclear. Here, the authors analyze its chromatin landscape at the single-cell level and define the epigenetic regulation of lineage fate decisions and plasticity in organ development and homeostasis.

The transcription factor hepatocyte nuclear factor 4A acts in the intestine to promote white adipose tissue energy storage

The transcription factor hepatocyte nuclear factor 4 A (HNF4A) controls the metabolic features of several endodermal epithelia. Both HNF4A and HNF4G are redundant in the intestine and it remains unclear whether HNF4A alone controls intestinal lipid metabolism. Here we show that intestinal HNF4A is not required for intestinal lipid metabolism per se, but unexpectedly influences whole-body energy expenditure in diet-induced obesity (DIO). Deletion of intestinal HNF4A caused mice to become DIO-resistant with a preference for fat as an energy substrate and energetic changes in association with white adipose tissue (WAT) beiging. Intestinal HNF4A is crucial for the fat-induced release of glucose-dependent insulinotropic polypeptide (GIP), while the reintroduction of a stabilized GIP analog rescues the DIO resistance phenotype of the mutant mice. Our study provides evidence that intestinal HNF4A plays a non-redundant role in whole-body lipid homeostasis and points to a non-cell-autonomous regulatory circuit for body-fat management.

HNF4A is a nuclear receptor that regulates liver lipid homeostasis. Here the authors show that HNF4A is not required for intestinal lipid metabolism but controls energy expenditure under diet induced obesity through the fat-induced release of glucose-dependent insulinotropic polypeptide.

Pseudogene RPL32P3 regulates the blood-tumor barrier permeability via the YBX2/HNF4G axis

The existence of the blood–tumor barrier (BTB) severely hinders the transport of anti-tumor drugs to brain tumor tissues. Selectively opening BTB is of great significance to improve the chemotherapy effect of glioma. Pseudogenes have been recognized as important regulators in various biologic processes. In this study, we identified that ribosomal protein L32 pseudogene 3 (RPL32P3) was highly expressed in glioma-exposed endothelial cells (GECs). Knockdown of RPL32P3 decreased the expression of tight junction-related proteins (TJPs) and increased BTB permeability. Subsequent analysis of the underlying mechanism indicated that RPL32P3 recruited lysine methyltransferase 2 A (KMT2A) to the Y-box binding protein 2 (YBX2) promoter region and mediated H3K4me3 to promote YBX2 transcription. Highly expressed YBX2 bound and stabilized hepatocyte nuclear factor 4 gamma (HNF4G) mRNA. Highly expressed HNF4G directly bound to the promoters of TJPs ZO-1, occludin and claudin-5 to promote their transcriptional activities and regulated BTB permeability. The simultaneous knockdown of RPL32P3, YBX2, and HNF4G combined with doxorubicin (DOX) increased the apoptosis of glioma cells. In conclusion, the current study indicated that RPL32P3 knockdown increased BTB permeability through the YBX2/HNF4G pathway. These findings may provide new targets for the comprehensive treatment of glioma.

HNF4A defines tissue-specific circadian rhythms by beaconing BMAL1::CLOCK chromatin binding and shaping the rhythmic chromatin landscape

Transcription modulated by the circadian clock is diverse across cell types, underlying circadian control of peripheral metabolism and its observed perturbation in human diseases. We report that knockout of the lineage-specifying Hnf4a gene in mouse liver causes associated reductions in the genome-wide distribution of core clock component BMAL1 and accessible chromatin marks (H3K4me1 and H3K27ac). Ectopically expressing HNF4A remodels chromatin landscape and nucleates distinct tissue-specific BMAL1 chromatin binding events, predominantly in enhancer regions. Circadian rhythms are disturbed in Hnf4a knockout liver and HNF4A-MODY diabetic model cells. Additionally, the epigenetic state and accessibility of the liver genome dynamically change throughout the day, synchronized with chromatin occupancy of HNF4A and clustered expression of circadian outputs. Lastly, Bmal1 knockout attenuates HNF4A genome-wide binding in the liver, likely due to downregulated Hnf4a transcription. Our results may provide a general mechanism for establishing circadian rhythm heterogeneity during development and disease progression, governed by chromatin structure.

The nuclear receptor HNF4 drives a brush border gene program conserved across murine intestine, kidney, and embryonic yolk sac

The brush border is comprised of microvilli surface protrusions on the apical surface of epithelia. This specialized structure greatly increases absorptive surface area and plays crucial roles in human health. However, transcriptional regulatory networks controlling brush border genes are not fully understood. Here, we identify that hepatocyte nuclear factor 4 (HNF4) transcription factor is a conserved and important regulator of brush border gene program in multiple organs, such as intestine, kidney and yolk sac. Compromised brush border gene signatures and impaired transport were observed in these tissues upon HNF4 loss. By ChIP-seq, we find HNF4 binds and activates brush border genes in the intestine and kidney. H3K4me3 HiChIP-seq identifies that HNF4 loss results in impaired chromatin looping between enhancers and promoters at gene loci of brush border genes, and instead enhanced chromatin looping at gene loci of stress fiber genes in the intestine. This study provides comprehensive transcriptional regulatory mechanisms and a functional demonstration of a critical role for HNF4 in brush border gene regulation across multiple murine epithelial tissues.

Dickkopf-2 regulates the stem cell marker LGR5 in colorectal cancer via HNF4α1

Enhanced stemness in colorectal cancer has been reported and it contributes to aggressive progression, but the underlying mechanisms remain unclear. Here we report a Wnt ligand, Dickkopf-2 (DKK2) is essential for developing colorectal cancer stemness. Genetic depletion of DKK2 in intestinal epithelial or stem cells reduced tumorigenesis and expression of the stem cell marker genes including LGR5 in a model of colitis-associated cancer. Sequential mutations in APC, KRAS, TP53, and SMAD4 genes in colonic organoids revealed a significant increase of DKK2 expression by APC knockout and further increased by additional KRAS and TP53 mutations. Moreover, DKK2 activates proto-oncogene tyrosine-protein kinse Src followed by increased LGR5 expressing cells in colorectal cancer through degradation of HNF4α1 protein. These findings suggest that DKK2 is required for colonic epithelial cells to enhance LGR5 expression during the progression of colorectal cancer.

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APC, KRAS, and TP53 mutations induce DKK2 expression in murine colon cancer

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DKK2 increases Src phosphorylation in colon cancer cells

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Activated Src leads to degradation of HNF4α1 protein

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This DKK2 downstream signaling enhances LGR5 expression in colon cancer

Three-dimensional interactions between enhancers and promoters during intestinal differentiation depend upon HNF4

Cells in renewing tissues exhibit dramatic transcriptional changes as they differentiate. The contribution of chromatin looping to tissue renewal is incompletely understood. Enhancer-promoter interactions could be relatively stable as cells transition from progenitor to differentiated states; alternatively, chromatin looping could be as dynamic as the gene expression from their loci. The intestinal epithelium is the most rapidly renewing mammalian tissue. Proliferative cells in crypts of Lieberkühn sustain a stream of differentiated cells that are continually shed into the lumen. We apply chromosome conformation capture combined with chromatin immunoprecipitation (HiChIP) and sequencing to measure enhancer-promoter interactions in progenitor and differentiated cells of the intestinal epithelium. Despite dynamic gene regulation across the differentiation axis, we find that enhancer-promoter interactions are relatively stable. Functionally, we find HNF4 transcription factors are required for chromatin looping at target genes. Depletion of HNF4 disrupts local chromatin looping, histone modifications, and target gene expression. This study provides insights into transcriptional regulatory mechanisms governing homeostasis in renewing tissues.

Chen et al. provide a survey of enhancer-promoter 3D looping in the intestinal epithelium by HiChIP, in vivo. They find that enhancer-promoter interactions are highly dependent upon the key intestinal transcription factor HNF4. Their findings provide insights into transcriptional regulatory mechanisms governing homeostasis in renewing tissues.

Transcriptional programmes underlying cellular identity and microbial responsiveness in the intestinal epithelium

The intestinal epithelium serves the unique and critical function of harvesting dietary nutrients, while simultaneously acting as a cellular barrier separating tissues from the luminal environment and gut microbial ecosystem. Two salient features of the intestinal epithelium enable it to perform these complex functions. First, cells within the intestinal epithelium achieve a wide range of specialized identities, including different cell types and distinct anterior-posterior patterning along the intestine. Second, intestinal epithelial cells are sensitive and responsive to the dynamic milieu of dietary nutrients, xenobiotics and microorganisms encountered in the intestinal luminal environment. These diverse identities and responsiveness of intestinal epithelial cells are achieved in part through the differential transcription of genes encoded in their shared genome. Here, we review insights from mice and other vertebrate models into the transcriptional regulatory mechanisms underlying intestinal epithelial identity and microbial responsiveness, including DNA methylation, chromatin accessibility, histone modifications and transcription factors. These studies are revealing that most transcription factors involved in intestinal epithelial identity also respond to changes in the microbiota, raising both opportunities and challenges to discern the underlying integrative transcriptional regulatory networks.

Control of Cell Identity by the Nuclear Receptor HNF4 in Organ Pathophysiology

Hepatocyte Nuclear Factor 4 (HNF4) is a transcription factor (TF) belonging to the nuclear receptor family whose expression and activities are restricted to a limited number of organs including the liver and gastrointestinal tract. In this review, we present robust evidence pointing to HNF4 as a master regulator of cellular differentiation during development and a safekeeper of acquired cell identity in adult organs. Importantly, we discuss that transient loss of HNF4 may represent a protective mechanism upon acute organ injury, while prolonged impairment of HNF4 activities could contribute to organ dysfunction. In this context, we describe in detail mechanisms involved in the pathophysiological control of cell identity by HNF4, including how HNF4 works as part of cell-specific TF networks and how its expression/activities are disrupted in injured organs.

Epigenetic regulation of intestinal stem cell differentiation

To fulfill the lifelong need to supply diverse epithelial cells, intestinal stem cells (ISCs) rely on executing accurate transcriptional programs. This review addresses the mechanisms that control those programs. Genes that define cell behaviors and identities are regulated principally through thousands of dispersed enhancers, each individually <1 kb long and positioned from a few to hundreds of kilobases away from transcription start sites, upstream or downstream from coding genes or within introns. Wnt, Notch, and other epithelial control signals feed into these cis-regulatory DNA elements, which are also common loci of polymorphisms and mutations that confer disease risk. Cell-specific gene activity requires promoters to interact with the correct combination of signal-responsive enhancers. We review the current state of knowledge in ISCs regarding active enhancers, the nucleosome modifications that may enable appropriate and hinder inappropriate enhancer-promoter contacts, and the roles of lineage-restricted transcription factors.