Histone Modifications in Stem Cell Development and Their Clinical Implications

Spatially resolved epigenome sequencing via Tn5 transposition and deterministic DNA barcoding in tissue

Spatial epigenetic mapping of tissues enables the study of gene regulation programs and cellular functions with the dependency on their local tissue environment. Here we outline a complete procedure for two spatial epigenomic profiling methods: spatially resolved genome-wide profiling of histone modifications using in situ cleavage under targets and tagmentation (CUT&Tag) chemistry (spatial-CUT&Tag) and transposase-accessible chromatin sequencing (spatial-ATAC-sequencing) for chromatin accessibility. Both assays utilize in-tissue Tn5 transposition to recognize genomic DNA loci followed by microfluidic deterministic barcoding to incorporate spatial address codes. Furthermore, these two methods do not necessitate prior knowledge of the transcription or epigenetic markers for a given tissue or cell type but permit genome-wide unbiased profiling pixel-by-pixel at the 10 μm pixel size level and single-base resolution. To support the widespread adaptation of these methods, details are provided in five general steps: (1) sample preparation; (2) Tn5 transposition in spatial-ATAC-sequencing or antibody-controlled pA-Tn5 tagmentation in CUT&Tag; (3) library preparation; (4) next-generation sequencing; and (5) data analysis using our customed pipelines available at: https://github.com/dyxmvp/Spatial_ATAC-seq and https://github.com/dyxmvp/spatial-CUT-Tag . The whole procedure can be completed on four samples in 2-3 days. Familiarity with basic molecular biology and bioinformatics skills with access to a high-performance computing environment are required. A rudimentary understanding of pathology and specimen sectioning, as well as deterministic barcoding in tissue-specific skills (e.g., design of a multiparameter barcode panel and creation of microfluidic devices), are also advantageous. In this protocol, we mainly focus on spatial profiling of tissue region-specific epigenetic landscapes in mouse embryos and mouse brains using spatial-ATAC-sequencing and spatial-CUT&Tag, but these methods can be used for other species with no need for species-specific probe design.

Exosomal Epigenetics

Epigenetics is the study of heritable changes in gene expression that occur without changes to the underlying DNA sequence. Epigenetic modifications can include DNA methylation, histone modifications, and non-coding RNAs, among others. These modifications can influence the expression of genes by altering the way DNA is packaged and accessed by transcriptional machinery, thereby affecting cellular function and behavior. Epigenetic modifications can be influenced by a variety of factors, including environmental exposures, lifestyle factors, and aging, whilst abnormal epigenetic modifications have been implicated in a range of diseases, including cancer, neurodegenerative disorders, and cardiovascular disease. The study of epigenetics has the potential to provide new insights into the mechanisms of disease and could lead to the development of new diagnostic and therapeutic strategies. Exosomes can transfer epigenetic information to recipient cells, thereby influencing various physiological and pathological processes, and the identification of specific epigenetic modifications that are associated with a particular disease could lead to the development of targeted therapies that restore normal gene expression patterns. In recent years, the emerging role of exosomal epigenetics in human breast milk, highlighting its significance in infant nutrition and immune development. Milk exosomes are shown to carry epigenetic regulators, including miRNAs and long non-coding RNAs, which can modulate gene expression in recipient cells. These epigenetic modifications mediated by milk exosomal RNAs have implications for the development of the gastrointestinal tract, immune system, and metabolic processes in infants.

Ptip is essential for tooth development via regulating Wnt pathway

OBJECTIVE

Epigenetic regulation plays important role in stem cell maintenance. Ptip was identified as epigenetic regulator, but the role in dental progenitor cells remains unclear.

SUBJECTS AND METHODS

Dental mesenchymal progenitor cells were targeted by Sp7-icre and visualized in mTmG; Sp7-icre mice. The Ptipf/f; Sp7-icre mice were generated and the phenotype of incisors and molars were shown by micro-computerized tomography, scanning electron microscope, hematoxylin & eosin staining, and immunofluorescence. Dental mesenchymal progenitor cells were sorted by fluorescence-activated cell sorting from lower incisors and RNA sequencing was performed.

RESULTS

The Sp7-icre targets dental mesenchymal progenitor cells in incisors and molars. The Ptipf/f; Sp7-icre mice showed spontaneous fractures in the cusp of upper incisors and lower incisors at 3 weeks (w), compensative overgrowth of lower incisors at 1 month (M), and overgrowth extended to the outside at 2 M. The molars showed shortened roots. The functions of odontoblasts and dental mesenchymal progenitor cells were impaired. Mechanically, loss of Ptip activates the Wnt pathway and upregulates the expression of Wls in dental mesenchymal progenitor cells. Also, the regenerative ability of lower incisors was significantly impaired.

CONCLUSION

We first demonstrated that Ptip was crucial for tooth development via regulating Wnt signaling.

Expression of stem cell markers as predictors of therapeutic response in metastatic prostate cancer patients

BACKGROUND

Cancer stem cells (CSCs) have been implicated in prostate cancer (PCA) progression and therapeutic resistance. This study aimed to compare the expression levels of CSC CD (CD 44, CD 133, and CD 24) markers in treatment-naive patients with metastatic PCA before and after treatment.

METHODS

The study included 60 treatment-naïve patients with metastatic PCA who received androgen deprivation therapy (ADT) alone (n = 30) and ADT plus chemotherapy (n = 30). The level of CD44, CD133, and CD24 were obtained by flow cytometric analysis before and after treatment. Baseline characteristics were also assessed, including age, pretreatment testosterone levels, and pretreatment prostate-specific antigen (PSA) levels.

RESULTS

The baseline characteristics analysis showed no significant difference in pre-treatment testosterone levels between the ADT+ chemotherapy and ADT-alone groups. In the flow cytometric analysis, no significant difference was observed in pre-treatment CD44+ and CD133+ levels between the 2 treatment groups, although a trend towards higher pretreatment CD24- levels was observed in the ADT+ chemotherapy group. After treatment, significant reductions in testosterone and PSA levels were observed in both treatment arms. The ADT+ chemotherapy group showed a greater reduction in CD44+ and CD133+ levels compared to the ADT-alone group. Bioinformatic analysis using the UALCAN TCGA database also showed a similar trend of CD 44, CD 24, and CD 133 gene expression patterns.

CONCLUSION

Combination therapy involving chemotherapy and ADT appears to have a greater impact on suppressing CSCs compared to ADT alone. These findings highlight the potential of targeting CSCs as a prognostic and predictive marker therapeutic strategy in metastatic PCA.

Dynamic and distinct histone modifications facilitate human trophoblast lineage differentiation

The placenta serves as an essential organ for fetal growth throughout pregnancy. Histone modification is a crucial regulatory mechanism involved in numerous biological processes and development. Nevertheless, there remains a significant gap in our understanding regarding the epigenetic regulations that influence trophoblast lineage differentiation, a fundamental aspect of placental development. Here, through comprehensive mapping of H3K4me3, H3K27me3, H3K9me3, and H3K27ac loci during the differentiation of trophoblast stem cells (TSCs) into syncytiotrophoblasts (STs) and extravillous trophoblasts (EVTs), we reveal dynamic reconfiguration in H3K4me3 and H3K27ac patterns that establish an epigenetic landscape conducive to proper trophoblast lineage differentiation. We observe that broad H3K4me3 domains are associated with trophoblast lineage-specific gene expression. Unlike embryonic stem cells, TSCs lack robust bivalent domains. Notably, the repression of ST- and EVT-active genes in TSCs is primarily attributed to the weak H3K4me3 signal rather than bivalent domains. We also unveil the inactivation of TSC enhancers precedes the activation of ST enhancers during ST formation. Our results provide a comprehensive global map of diverse histone modifications, elucidating the dynamic histone modifications during trophoblast lineage differentiation.

Functional genomics in Spiralia

Our understanding of the mechanisms that modulate gene expression in animals is strongly biased by studying a handful of model species that mainly belong to three groups: Insecta, Nematoda and Vertebrata. However, over half of the animal phyla belong to Spiralia, a morphologically and ecologically diverse animal clade with many species of economic and biomedical importance. Therefore, investigating genome regulation in this group is central to uncovering ancestral and derived features in genome functioning in animals, which can also be of significant societal impact. Here, we focus on five aspects of gene expression regulation to review our current knowledge of functional genomics in Spiralia. Although some fields, such as single-cell transcriptomics, are becoming more common, the study of chromatin accessibility, DNA methylation, histone post-translational modifications and genome architecture are still in their infancy. Recent efforts to generate chromosome-scale reference genome assemblies for greater species diversity and optimise state-of-the-art approaches for emerging spiralian research systems will address the existing knowledge gaps in functional genomics in this animal group.

Talazoparib enhances the quinacrine-mediated apoptosis in patient-derived oral mucosa CSCs by inhibiting BER pathway through the modulation of GCN5 and P300

The presence of cancer stem cells (CSCs) in the tumor microenvironment (TME) is majorly responsible for the development and recurrence of cancer. Earlier reports suggested that upon DNA damage, poly-(ADP-ribose) polymerase-1 (PARP-1) helps in chromatin modulation and DNA repair process, thereby promoting CSC survival. But whether a combination of DNA damaging agents along with PARP inhibitors can modulate chromatin assembly, inhibit DNA repair processes, and subsequently target CSCs is not known. Hence, we have investigated the effect of nontoxic bioactive compound quinacrine (QC) and a potent PARP inhibitor Talazoparib in patient-derived oral mucosa CSCs (OM-CSCs) and in vivo xenograft mice preclinical model systems. Data showed that QC + Talazoparib inhibited the PARP-1-mediated chromatin remodelers' recruitment and deregulated HAT activity of GCN5 (general control nonderepressible-5) and P300 at DNA damage site, thereby preventing the access of repair proteins to the damaged DNA. Additionally, this combination treatment inhibited topoisomerase activity, induced topological stress, and induced apoptosis in OM-CSCs. Similar results were observed in an in vivo xenograft mice model system. Collectively, the data suggested that QC + Talazoparib treatment inhibited BER pathway, induced genomic instability and triggered apoptosis in OM-CSCs through the deregulation of PARP-1-mediated chromatin remodelers (GCN5 and P300) activity. Schematic representation of QC + Talazoparib-induced apoptosis in oral mucosa CSCs. (1) Induction of DNA damage takes place after QC treatment (2) PARP1-mediated PARylation at the site of DNA damage, which recruits multiple chromatin remodelers (3) Acetylation at the histone tails relax the structure of chromatin and recruits the BER pathway proteins at the site of DNA damage. (4) BER pathway activated at the site of DNA damage. (5) CSCs survive after successful repair of DNA damage. (6) Treatment of QC-treated CSCs with PARP inhibitor Talazoparib (7) Inhibition of PARylation results in failure of chromatin remodelers to interact with PARP1. (8) Inhibition of acetylation status leads to chromatin compaction. (9) BER pathway proteins are not recruited at the site of DNA damage, resulting in inhibition of BER pathway and accumulation of unrepaired DNA damage, leading to apoptosis and cell death.

Epigenetic control of cell signalling in cancer stem cells

The self-renewing cancer stem cells (CSCs) represent one of the distinct cell populations occurring in a tumour that can differentiate into multiple lineages. This group of sparsely abundant cells play a vital role in tumour survival and resistance to different treatments during cancer. The lack of exclusive markers associated with CSCs makes diagnosis and prognosis in cancer patients extremely difficult. This calls for the identification of unique regulators and markers for CSCs. Various signalling pathways like the Wnt/β-catenin pathway, Hedgehog pathway, Notch pathway, and TGFβ/BMP play a major role in the regulation and maintenance of CSCs. Epigenetic regulatory mechanisms add another layer of complexity to control these signalling pathways. In this chapter, we discuss about the role of epigenetic mechanisms in regulating the cellular signalling pathways in CSCs. The epigenetic regulatory mechanisms such as DNA methylation, histone modification and microRNAs can modulate the diverse effectors of signalling pathways and consequently the growth, differentiation and tumorigenicity of CSCs. In the end, we briefly discuss the therapeutic potential of targeting these epigenetic regulators and their target genes in CSCs.

Microbiota-Derived Natural Products Targeting Cancer Stem Cells: Inside the Gut Pharma Factory

Cancer stem cells (CSCs) have drawn much attention as important tumour-initiating cells that may also be crucial for recurrence after chemotherapy. Although the activity of CSCs in various forms of cancer is complex and yet to be fully elucidated, opportunities for therapies targeting CSCs exist. CSCs are molecularly distinct from bulk tumour cells, so they can be targeted by exploiting their signature molecular pathways. Inhibiting stemness has the potential to reduce the risk posed by CSCs by limiting or eliminating their capacity for tumorigenesis, proliferation, metastasis, and recurrence. Here, we briefly described the role of CSCs in tumour biology, the mechanisms involved in CSC therapy resistance, and the role of the gut microbiota in cancer development and treatment, to then review and discuss the current advances in the discovery of microbiota-derived natural compounds targeting CSCs. Collectively, our overview suggests that dietary intervention, toward the production of those identified microbial metabolites capable of suppressing CSC properties, is a promising approach to support standard chemotherapy.

H H, Bharathavikru RS. Resetting the epigenome: Methylation dynamics in cancer stem cells

The molecular mechanisms that regulate stem cell pluripotency and differentiation has shown the crucial role that methylation plays in this process. DNA methylation has been shown to be important in the context of developmental pathways, and the role of histone methylation in establishment of the bivalent state of genes is equally important. Recent studies have shed light on the role of RNA methylation changes in stem cell biology. The dynamicity of these methylation changes not only regulates the effective maintenance of pluripotency or differentiation, but also provides an amenable platform for perturbation by cellular stress pathways that are inherent in immune responses such as inflammation or oncogenic programs involving cancer stem cells. We summarize the recent research on the role of methylation dynamics and how it is reset during differentiation and de-differentiation.

Single cell cancer epigenetics

Bulk sequencing methodologies have allowed us to make great progress in cancer research. Unfortunately, these techniques lack the resolution to fully unravel the epigenetic mechanisms that govern tumor heterogeneity. Consequently, many novel single cell-sequencing methodologies have been developed over the past decade, allowing us to explore the epigenetic components that regulate different aspects of cancer heterogeneity, namely: clonal heterogeneity, tumor microenvironment (TME), spatial organization, intratumoral differentiation programs, metastasis, and resistance mechanisms. In this review, we explore the different sequencing techniques that enable researchers to study different aspects of epigenetics (DNA methylation, chromatin accessibility, histone modifications, DNA-protein interactions, and chromatin 3D architecture) at the single cell level, their potential applications in cancer, and their current technical limitations.

Dynamic spreading of chromatin-mediated gene silencing and reactivation between neighboring genes in single cells

In mammalian cells genes that are in close proximity can be transcriptionally coupled: silencing or activating one gene can affect its neighbors. Understanding these dynamics is important for natural processes, such as heterochromatin spreading during development and aging, and when designing synthetic gene regulation circuits. Here, we systematically dissect this process in single cells by recruiting and releasing repressive chromatin regulators at dual-gene synthetic reporters, and measuring how fast gene silencing and reactivation spread as a function of intergenic distance and configuration of insulator elements. We find that silencing by KRAB, associated with histone methylation, spreads between two genes within hours, with a time delay that increases with distance. This fast KRAB-mediated spreading is not blocked by the classical cHS4 insulators. Silencing by histone deacetylase HDAC4 of the upstream gene can also facilitate background silencing of the downstream gene by PRC2, but with a days-long delay that does not change with distance. This slower silencing can sometimes be stopped by insulators. Gene reactivation of neighboring genes is also coupled, with strong promoters and insulators determining the order of reactivation. Our data can be described by a model of multi-gene regulation that builds upon previous knowledge of heterochromatin spreading, where both gene silencing and gene reactivation can act at a distance, allowing for coordinated dynamics via chromatin regulator recruitment.

Why stem/progenitor cells lose their regenerative potential

Nowadays, it is clear that adult stem cells, also called as tissue stem cells, play a central role to repair and maintain the tissue in which they reside by their self-renewal ability and capacity of differentiating into distinct and specialized cells. As stem cells age, their renewal ability declines and their capacity to maintain organ homeostasis and regeneration is impaired. From a molecular perspective, these changes in stem cells properties can be due to several types of cell intrinsic injury and DNA aberrant alteration (i.e epigenomic profile) as well as changes in the tissue microenviroment, both into the niche and by systemic circulating factors. Strikingly, it has been suggested that aging-induced deterioration of stem cell functions may play a key role in the pathophysiology of the various aging-associated disorders. Therefore, understanding how resident stem cell age and affects near and distant tissues is fundamental. Here, we examine the current knowledge about aging mechanisms in several kinds of adult stem cells under physiological and pathological conditions and the principal aging-related changes in number, function and phenotype that determine the loss of tissue renewal properties. Furthermore, we examine the possible cell rejuvenation strategies. Stem cell rejuvenation may reverse the aging phenotype and the discovery of effective methods for inducing and differentiating pluripotent stem cells for cell replacement therapies could open up new possibilities for treating age-related diseases.

Bivalent Regulation and Related Mechanisms of H3K4/27/9me3 in Stem Cells

The "bivalent domain" is a unique histone modification region consisting of two histone tri-methylation modifications. Over the years, it has been revealed that the maintenance and dynamic changes of the bivalent domains play a vital regulatory role in the differentiation of various stem cell systems, as well as in other cells, such as immunomodulation. Tri-methylation modifications involved in the formation of the bivalent domains are interrelated and mutually regulated, thus regulating many life processes of cells. Tri-methylation of histone H3 at lysine 4 (H3K4me3), tri-methylation of histone H3 at lysine 9 (H3K9me3) and tri-methylation of histone H3 at lysine 27 (H3K27me3) are the main tri-methylation modifications involved in the formation of bivalent domains. The three form different bivalent domains in pairs. Furthermore, it is equally clear that H3K4me3 is a positive regulator of transcription and that H3K9me3/H3K27me3 are negative regulators. Enzymes related to the regulation of histone methylation play a significant role in the "homeostasis" and "breaking homeostasis" of the bivalent domains. Bivalent domains regulate target genes, upstream transcription, downstream targeting regulation and related cytokines during the establishment and breakdown of homeostasis, and exert the specific regulation of stem cells. Indeed, a unified mechanism to explain the bivalent modification in all stem cells has been difficult to define, and whether the bivalent modification is antagonistic in inducing the differentiation of homologous stem cells is controversial. In this review, we focus on the different bivalent modifications in several key stem cells and explore the main mechanisms and effects of these modifications involved. Finally, we discussed the close relationship between bivalent domains and immune cells, and put forward the prospect of the application of bivalent domains in the field of stem cells.

Signaling pathways governing breast cancer stem cells behavior

Breast cancer is the second common cancer and the leading cause of malignancy among females overall. Breast cancer stem cells (BCSCs) are a small population of breast cancer cells that play a critical role in the metastasis of breast cancer to other organs in the body. BCSCs have both self-renewal and differentiation capacities, which are thought to contribute to the aggressiveness of metastatic lesions. Therefore, targeting BCSCs can be a suitable approach for the treatment and metastasis of breast cancer. Growing evidence has indicated that the Wnt, NFκB, Notch, BMP2, STAT3, and hedgehog (Hh) signaling pathways govern epithelial-to-mesenchymal transition (EMT) activation, growth, and tumorigenesis of BCSCs in the primary regions. miRNAs as the central regulatory molecules also play critical roles in BCSC self-renewal, metastasis, and drug resistance. Hence, targeting these pathways might be a novel therapeutic approach for breast cancer diagnosis and therapy. This review discusses known signaling mechanisms involved in the stimulation or prevention of BCSC self-renewal, metastasis, and tumorigenesis.

Chromatin and Nuclear Architecture in Stem Cells

Here we outline the contents of Stem Cell Reports' first special issue, on chromatin and nuclear architecture in stem cells. It features both reviews and original research articles, covering emerging topics in nuclear architecture including 3D genome organization in stem cells and early development, membraneless organelles, epigenetics-related therapy, and more.