A transit-amplifying progenitor with biphasic behavior contributes to epidermal renewal.

Transit-amplifying (TA) cells are progenitors that undergo an amplification phase followed by transition into an extinction phase. A long postulated epidermal TA progenitor with biphasic behavior has not yet been experimentally observed in vivo. Here, we identify such a TA population using clonal analysis of Aspm-CreER genetic cell-marking in mice, which uncovers contribution to both homeostasis and injury repair of adult skin. This TA population is more frequently dividing than a Dlx1-CreER-marked long-term self-renewing (e.g. stem cell) population. Newly developed generalized birth-death modeling of long-term lineage tracing data shows that both TA progenitors and stem cells display neutral competition, but only the stem cells display neutral drift. The quantitative evolution of a nascent TA cell and its direct descendants shows that TA progenitors indeed amplify the basal layer before transition and that the homeostatic TA population is mostly in extinction phase. This model will be broadly useful for analyzing progenitors whose behavior changes with their clone age. This work identifies a long-missing class of non-self-renewing biphasic epidermal TA progenitors and has broad implications for understanding tissue renewal mechanisms.

Depletion of NIMA-related kinase Nek2 induces aberrant self-renewal and apoptosis in stem/progenitor cells of aged muscular tissues.

Frailty of the locomotory organs has become a widespread problem in the geriatric population. The major factor leading to frailty is an age-associated decrease in muscular mass and a reduced number of muscular cells and myofibers. In aged muscular tissues, muscular satellite cells (MuSCs) are reduced due to abnormalities in their self-renewal and the induction of apoptosis. However, the molecular mechanisms connecting aging-associated physiological changes and the reduction of MuSCs are largely unknown. NIMA-related kinase 2 (Nek2), a member of the Nek family of serine/threonine kinases, was found to be downregulated in aged MuSCs/progenitors. Further, Nek2 downregulation was found to inhibit self-renewal and apoptotic cell death by activating the p53-dependent checkpoint. Attenuated NEK2 expression was also observed in the muscular tissues of elderly donors, and its function was confirmed to be conserved in humans. Overall, this study proposes a novel mechanism for inducing muscular atrophy to understand aging-associated muscular diseases.

Differentiation of fetal hematopoietic stem cells requires ARID4B to restrict autocrine KITLG/KIT-Src signaling.

Balance between the hematopoietic stem cell (HSC) duality to either possess self-renewal capacity or differentiate into multipotency progenitors (MPPs) is crucial for maintaining homeostasis of the hematopoietic stem/progenitor cell (HSPC) compartment. To retain the HSC self-renewal activity, KIT, a receptor tyrosine kinase, in HSCs is activated by its cognate ligand KITLG originating from niche cells. Here, we show that AT-rich interaction domain 4B (ARID4B) interferes with KITLG/KIT signaling, consequently allowing HSC differentiation. Conditional Arid4b knockout in mouse hematopoietic cells blocks fetal HSC differentiation, preventing hematopoiesis. Mechanistically, ARID4B-deficient HSCs self-express KITLG and overexpress KIT. As to downstream pathways of KITLG/KIT signaling, inhibition of Src family kinases rescues the HSC differentiation defect elicited by ARID4B loss. In summary, the intrinsic ARID4B-KITLG/KIT-Src axis is an HSPC regulatory program that enables the differentiation state, while KIT stimulation by KITLG from niche cells preserves the HSPC undifferentiated pool.

The tumor suppression theory of aging.

Despite continued increases in human life expectancy, the factors determining the rate of human biological aging remain unknown. Without understanding the molecular mechanisms underlying aging, efforts to prevent aging are unlikely to succeed. The tumor suppression theory of aging introduced here proposes somatic mutation as the proximal cause of aging, but postulates that oncogenic transformation and clonal expansion, not functional impairment, are the relevant consequences of somatic mutation. Obesity and caloric restriction accelerate and decelerate aging due to their effect on cell proliferation, during which most mutations arise. Most phenotypes of aging are merely tumor-suppressive mechanisms that evolved to limit malignant growth, the dominant age-related cause of death in early and middle life. Cancer limits life span for most long-lived mammals, a phenomenon known as Peto's paradox. Its conservation across species demonstrates that mutation is a fundamental but hard limit on mammalian longevity. Cell senescence and apoptosis and differentiation induced by oncogenes, telomere shortening or DNA damage evolved as a second line of defense to limit the tumorigenic potential of clonally expanding cells, but accumulating senescent cells, senescence-associated secretory phenotypes and stem cell exhaustion eventually cause tissue dysfunction and the majority, if not most, phenotypes of aging.

Probing ß-Cell Biology in Space and Time.

ß-Cells in the islet of Langerhans have a central role in maintaining energy homeostasis. Understanding the physiology of ß-cells and other islet cells requires a deep understanding of their structural and functional organization, their interaction with vessels and nerves, the layout of paracrine interactions, and the relationship between subcellular compartments and protein complexes inside each cell. These elements are not static; they are dynamic and exert their biological actions at different scales of time. Therefore, scientists must be able to investigate (and visualize) short- and long-lived events within the pancreas and ß-cells. Current technological advances in microscopy are able to bridge multiple spatiotemporal scales in biology to reveal the complexity and heterogeneity of ß-cell biology. Here, I briefly discuss the historical discoveries that leveraged microscopes to establish the basis of ß-cell anatomy and structure, the current imaging platforms that allow the study of islet and ß-cell biology at multiple scales of resolution, and their challenges and implications. Lastly, I outline how the remarkable longevity of structural elements at different scales in biology, from molecules to cells to multicellular structures, could represent a previously unrecognized organizational pattern in developing and adult ß-cells and pancreas biology.

Cilium induction triggers differentiation of glioma stem cells.

Glioblastoma multiforme (GBM) possesses glioma stem cells (GSCs) that promote self-renewal, tumor propagation, and relapse. Understanding the mechanisms of GSCs self-renewal can offer targeted therapeutic interventions. However, insufficient knowledge of GSCs' fundamental biology is a significant bottleneck hindering these efforts. Here, we show that patient-derived GSCs recruit elevated levels of proteins that ensure the temporal cilium disassembly, leading to suppressed ciliogenesis. Depleting the cilia disassembly complex components is sufficient to induce ciliogenesis in a subset of GSCs via relocating platelet-derived growth factor receptor-alpha (PDGFR-α) to a newly induced cilium. Importantly, restoring ciliogenesis enabled GSCs to switch from self-renewal to differentiation. Finally, using an organoid-based glioma invasion assay and brain xenografts in mice, we establish that ciliogenesis-induced differentiation can prevent the infiltration of GSCs into the brain. Our findings illustrate a role for cilium as a molecular switch in determining GSCs' fate and suggest cilium induction as an attractive strategy to intervene in GSCs proliferation.

DOC-2/DAB2 interactive protein destabilizes c-Myc to impair the growth and self-renewal of colon tumor-repopulating cells.

Colorectal carcinoma (CRC) remains a huge challenge in clinical treatment due to tumor metastasis and recurrence. Stem cell-like colon tumor-repopulating cells (TRCs) are a subpopulation of cancer cells with highly tumorigenic and chemotherapy resistant properties. The core transcription factor c-Myc is essential for maintaining cancer stem-like cell phenotypes, yet its roles and regulatory mechanisms remain unclear in colon TRCs. We report that elevated c-Myc protein supported formation and growth of TRC spheroids. The tumor suppressor DOC-2/DAB2 interactive protein (DAB2IP) suppressed c-Myc expression to inhibit TRC expansion and self-renewal. Particularly, DAB2IP disrupted c-Myc stability through glycogen synthase kinase 3ß/protein phosphatase 2A-B56α-mediated phosphorylation and dephosphorylation cascade on c-Myc protein, leading to its eventual degradation through the ubiquitin-proteasome pathway. The expression of DAB2IP was negatively correlated with c-Myc in CRC specimens. Overall, our results improved mechanistic insight into how DAB2IP suppressed TRC growth and self-renewal.

The related coactivator complexes SAGA and ATAC control embryonic stem cell self-renewal through acetyltransferase-independent mechanisms.

SAGA (Spt-Ada-Gcn5 acetyltransferase) and ATAC (Ada-two-A-containing) are two related coactivator complexes, sharing the same histone acetyltransferase (HAT) subunit. The HAT activities of SAGA and ATAC are required for metazoan development, but the role of these complexes in RNA polymerase II transcription is less understood. To determine whether SAGA and ATAC have redundant or specific functions, we compare the effects of HAT inactivation in each complex with that of inactivation of either SAGA or ATAC core subunits in mouse embryonic stem cells (ESCs). We show that core subunits of SAGA or ATAC are required for complex assembly and mouse ESC growth and self-renewal. Surprisingly, depletion of HAT module subunits causes a global decrease in histone H3K9 acetylation, but does not result in significant phenotypic or transcriptional defects. Thus, our results indicate that SAGA and ATAC are differentially required for self-renewal of mouse ESCs by regulating transcription through different pathways in a HAT-independent manner.

The transcription factor ZEB1 regulates stem cell self-renewal and cell fate in the adult hippocampus.

Radial glia-like (RGL) stem cells persist in the adult mammalian hippocampus, where they generate new neurons and astrocytes throughout life. The process of adult neurogenesis is well documented, but cell-autonomous factors regulating neuronal and astroglial differentiation are incompletely understood. Here, we evaluate the functions of the transcription factor zinc-finger E-box binding homeobox 1 (ZEB1) in adult hippocampal RGL cells using a conditional-inducible mouse model. We find that ZEB1 is necessary for self-renewal of active RGL cells. Genetic deletion of Zeb1 causes a shift toward symmetric cell division that consumes the RGL cell and generates pro-neuronal progenies, resulting in an increase of newborn neurons and a decrease of newly generated astrocytes. We identify ZEB1 as positive regulator of the ets-domain transcription factor ETV5 that is critical for asymmetric division.

L-myc Gene Expression in Canine Fetal Fibroblasts Promotes Self-Renewal Capacity but Not Tumor Formation.

Canines are useful in mammalian preclinical studies because they are larger than rodents and share many diseases with humans. Canine fetal fibroblast cells (CFFs) are an easily accessible source of somatic cells. However, they are easily driven to senescence and become unusable with continuous in vitro culture. Therefore, to overcome these deficiencies, we investigated whether tetracycline-inducible L-myc gene expression promotes self-renewal activity and tumorigenicity in the production of induced conditional self-renewing fibroblast cells (iCSFCs). Here, we describe the characterization of a new iCSFC line immortalized by transduction with L-myc that displays in vitro self-renewal ability without tumorigenic capacity. We established conditionally inducible self-renewing fibroblast cells by transducing CFF-3 cells with L-myc under the tetracycline-inducible gene expression system. In the absence of doxycycline, the cells did not express L-myc or undergo self-renewal. The iCSFCs had a fibroblast-like morphology, normal chromosome pattern, and expressed fibroblast-specific genes and markers. However, the iCSFCs did not form tumors in a soft agar colony-forming assay. We observed higher expression of three ES modules (core pluripotency genes, polycomb repressive complex genes (PRC), and MYC-related genes) in the iCSFCs than in the CFF-3 cells; in particular, the core pluripotency genes (OCT4, SOX2, and NANOG) were markedly up-regulated compared with the PRC and MYC module genes. These results demonstrated that, in canine fetal fibroblasts, L-myc tetracycline-inducible promoter-driven gene expression induces self-renewal capacity but not tumor formation. This study suggests that L-myc gene-induced conditional self-renewing fibroblast cells can be used as an in vitro tool in a variety of biomedical studies related to drug screening.

Leukemogenesis via aberrant self-renewal by the MLL/AEP-mediated transcriptional activation system.

Homeostasis of the hematopoietic system is achieved in a hierarchy, with hematopoietic stem cells at the pinnacle. Because only hematopoietic stem cells (HSCs) can self-renew, the size of the hematopoietic system is strictly controlled. In hematopoietic reconstitution experiments, 1 HSC can reconstitute the entire hematopoietic system, whereas 50 multipotent progenitors cannot. This indicates that only HSCs self-renew, whereas non-HSC hematopoietic progenitors are programmed to differentiate or senesce. Oncogenic mutations of the mixed lineage leukemia gene (MLL) overcome this "programmed differentiation" by conferring the self-renewing ability to non-HSC hematopoietic progenitors. In leukemia, mutated MLL proteins constitutively activate a broad range of previously transcribed CpG-rich promoters by an MLL-mediated transcriptional activation system. This system promotes self-renewal by replicating an expression profile similar to that of the mother cell in its daughter cells. In this transcriptional activation system, MLL binds to unmethylated CpG-rich promoters and recruits RNA polymerase II. MLL recruits p300/CBP through its transcriptional activation domain, which acetylates histone H3 at lysines 9, 18, and 27. The AF4 family/ENL family/P-TEFb complex (AEP) binds to acetylated H3K9/18/27 to activate transcription. Gene rearrangements of MLL with AEP- or CBP/p300-complex components generate constitutively active transcriptional machinery of this transcriptional activation system, which causes aberrant self-renewal of leukemia stem cells. Inhibitors of the components of this system effectively decrease their leukemogenic potential.

Universal principles of lineage architecture and stem cell identity in renewing tissues.

Adult tissues in multicellular organisms typically contain a variety of stem, progenitor and differentiated cell types arranged in a lineage hierarchy that regulates healthy tissue turnover. Lineage hierarchies in disparate tissues often exhibit common features, yet the general principles regulating their architecture are not known. Here, we provide a formal framework for understanding the relationship between cell molecular 'states' and cell 'types', based on the topology of admissible cell state trajectories. We show that a self-renewing cell type - if defined as suggested by this framework - must reside at the top of any homeostatic renewing lineage hierarchy, and only there. This architecture arises as a natural consequence of homeostasis, and indeed is the only possible way that lineage architectures can be constructed to support homeostasis in renewing tissues. Furthermore, under suitable feedback regulation, for example from the stem cell niche, we show that the property of 'stemness' is entirely determined by the cell environment, in accordance with the notion that stem cell identities are contextual and not determined by hard-wired, cell-intrinsic characteristics. This article has an associated 'The people behind the papers' interview.

YY2 in Mouse Preimplantation Embryos and in Embryonic Stem Cells.

Yin Yang 2 encodes a mammalian-specific transcription factor (YY2) that shares high homology in the zinc finger region with both YY1 and REX1/ZFP42, encoded by the Yin Yang 1 and Reduced Expression Protein 1/Zinc Finger Protein 42 gene, respectively. In contrast to the well-established roles of the latter two in gene regulation, X chromosome inactivation and binding to specific transposable elements (TEs), much less is known about YY2, and its presence during mouse preimplantation development has not been described. As it has been reported that mouse embryonic stem cells (mESC) cannot be propagated in the absence of Yy2, the mechanistic understanding of how Yy2 contributes to mESC maintenance remains only very partially characterized. We describe Yy2 expression studies using RT-PCR and staining with a high-affinity polyclonal serum in mouse embryos and mESC. Although YY2 is expressed during preimplantation development, its presence appears dispensable for developmental progress in vitro until formation of the blastocyst. Attenuation of Yy2 levels failed to alter either Zscan4 levels in two-cell embryos or IAP and MERVL levels at later preimplantation stages. In contrast to previous claims that constitutively expressed shRNA against Yy2 in mESC prohibited the propagation of mESC in culture, we obtained colonies generated from mESC with attenuated Yy2 levels. Concomitant with a decreased number of undifferentiated colonies, Yy2-depleted mESC expressed higher levels of Zscan4 but no differences in the expression of TEs or other pluripotency markers including Sox2, Oct4, Nanog and Esrrb were observed. These results confirm the contribution of Yy2 to the maintenance of mouse embryonic stem cells and show the preimplantation expression of YY2. These functions are discussed in relation to mammalian-specific functions of YY1 and REX1.

Self­renewal signaling pathways and differentiation therapies of glioblastoma stem cells (Review).

Glioblastoma multiforme (GBM) is a primary brain tumor with a high mortality rate and a median survival time of ~14 months from the initial diagnosis. Although progress has been made in the currently available therapies, the treatment of GBM remains palliative. GBM contains subsets of GBM stem cells (GSCs) that share numerous neural stem/progenitor cell characteristics, such as expression of stem cell markers, self­renewal and multi­lineage differentiation capacity, thus contributing to the heterogeneity and complexity of these tumors. GSCs are potentially associated with tumor initiation and they are considered as the driving force behind tumor formation, as they possess tumor­propagating potential and exhibit preferential resistance to radiotherapy and chemotherapy. Targeting self­renewal signaling pathways in cancer stem cells may effectively reduce tumor recurrence and significantly improve prognosis. The aim of the present review was to summarize the current knowledge on the self­renewal signaling pathways of GSCs and discuss potential future targeting strategies for the design of differentiation therapies.

Adrenal cortex renewal in health and disease.

Resident progenitor and/or stem cell populations in the adult adrenal cortex enable cortical cells to undergo homeostatic renewal and regeneration after injury. Renewal occurs predominantly in the outer layers of the adrenal gland but newly formed cells undergo centripetal migration, differentiation and lineage conversion in the process of forming the different functional steroidogenic zones. Over the past 10 years, advances in the genetic characterization of adrenal diseases and studies of mouse models with altered adrenal phenotypes have helped to elucidate the molecular pathways that regulate adrenal tissue renewal, several of which are fine-tuned via complex paracrine and endocrine influences. Moreover, the adrenal gland is a sexually dimorphic organ, and testicular androgens have inhibitory effects on cell proliferation and progenitor cell recruitment in the adrenal cortex. This Review integrates these advances, including the emerging role of sex hormones, into existing knowledge on adrenocortical cell renewal. An in-depth understanding of these mechanisms is expected to contribute to the development of novel therapies for severe endocrine diseases, for which current treatments are unsatisfactory.

Hypothalamic Rax+ tanycytes contribute to tissue repair and tumorigenesis upon oncogene activation in mice.

Hypothalamic tanycytes in median eminence (ME) are emerging as a crucial cell population that regulates endocrine output, energy balance and the diffusion of blood-born molecules. Tanycytes have recently been considered as potential somatic stem cells in the adult mammalian brain, but their regenerative and tumorigenic capacities are largely unknown. Here we found that Rax+ tanycytes in ME of mice are largely quiescent but quickly enter the cell cycle upon neural injury for self-renewal and regeneration. Mechanistically, Igf1r signaling in tanycytes is required for tissue repair under injury conditions. Furthermore, Braf oncogenic activation is sufficient to transform Rax+ tanycytes into actively dividing tumor cells that eventually develop into a papillary craniopharyngioma-like tumor. Together, these findings uncover the regenerative and tumorigenic potential of tanycytes. Our study offers insights into the properties of tanycytes, which may help to manipulate tanycyte biology for regulating hypothalamic function and investigate the pathogenesis of clinically relevant tumors.

Phosphorylation state of the histone variant H2A.X controls human stem and progenitor cell fate decisions.

Histone variants (HVs) are a subfamily of epigenetic regulators implicated in embryonic development, but their role in human stem cell fate remains unclear. Here, we reveal that the phosphorylation state of the HV H2A.X (γH2A.X) regulates self-renewal and differentiation of human pluripotent stem cells (hPSCs) and leukemic progenitors. As demonstrated by CRISPR-Cas deletion, H2A.X is essential in maintaining normal hPSC behavior. However, reduced levels of γH2A.X enhances hPSC differentiation toward the hematopoietic lineage with concomitant inhibition of neural development. In contrast, activation and sustained levels of phosphorylated H2A.X enhance hPSC neural fate while suppressing hematopoiesis. This controlled lineage bias correlates to occupancy of γH2A.X at genomic loci associated with ectoderm versus mesoderm specification. Finally, drug modulation of H2A.X phosphorylation overcomes differentiation block of patient-derived leukemic progenitors. Our study demonstrates HVs may serve to regulate pluripotent cell fate and that this biology could be extended to somatic cancer stem cell control.

Premature ovarian insufficiency: pathogenesis and therapeutic potential of mesenchymal stem cell.

Primary ovarian insufficiency (POI) is defined as a reduction in ovarian function before the expected age of menopause. POI is known to increase the risk of cardiovascular disorders, osteoporosis, cognitive decline, and mood disorders, resulting in a reduced quality of life. Appropriate hormone replacement for premenopausal women decreases these adverse health risks and improves quality of life for women with POI, but does not prolong life expectancy. The potential etiologies of POI include chromosomal abnormalities and genetic mutations, autoimmune factors, and iatrogenic causes, including surgery, chemotherapy, and radiation therapy. A major association is suggested to exist between reproductive longevity and the DNA damage pathway response genes. DNA damage and repair in ovarian granulosa cells is strongly associated with POI. Depletion of oocytes with damaged DNA occurs through different cell death mechanisms, such as apoptosis, autophagy, and necroptosis, mediated by the phosphatase and tensin homolog (PTEN)/phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/forkhead transcription factors 3 (FOXO3) pathway. Mesenchymal stem cells (MSCs) are characterized by the ability of self-renewal and differentiation and play an important role in the regeneration of injured tissues. Transplantation of MSCs has been shown to functionally restore ovarian reserve in a POI mouse model. Recent advances in stem cell therapy are likely to be translated to new therapeutic options bringing new hope to patients with POI. The aim of this review is to summarize the pathogenic mechanisms that involve cell death and DNA damage and repair pathways and to discuss the stem cell-based therapies as potential therapeutic options for this gynecologic pathology.

Role of c-Myc haploinsufficiency in the maintenance of HSCs in mice.

This study was conducted to determine the dosage effect of c-Myc on hematopoiesis and its distinct role in mediating the Wnt/ß-catenin pathway in hematopoietic stem cell (HSC) and bone marrow niche cells. c-Myc haploinsufficiency led to ineffective hematopoiesis by inhibiting HSC self-renewal and quiescence and by promoting apoptosis. We have identified Nr4a1, Nr4a2, and Jmjd3, which are critical for the maintenance of HSC functions, as previously unrecognized downstream targets of c-Myc in HSCs. c-Myc directly binds to the promoter regions of Nr4a1, Nr4a2, and Jmjd3 and regulates their expression. Our results revealed that Nr4a1 and Nr4a2 mediates the function of c-Myc in regulating HSC quiescence, whereas all 3 genes contribute to the function of c-Myc in the maintenance of HSC survival. Adenomatous polyposis coli (Apc) is a negative regulator of the Wnt/ß-catenin pathway. We have provided the first evidence that Apc haploinsufficiency induces a blockage of erythroid lineage differentiation through promoting secretion of IL6 in bone marrow endothelial cells. We found that c-Myc haploinsufficiency failed to rescue defective function of Apc-deficient HSCs in vivo but it was sufficient to prevent the development of severe anemia in Apc-heterozygous mice and to significantly prolong the survival of those mice. Furthermore, we showed that c-Myc-mediated Apc loss induced IL6 secretion in endothelial cells, and c-Myc haploinsufficiency reversed the negative effect of Apc-deficient endothelial cells on erythroid cell differentiation. Our studies indicate that c-Myc has a context-dependent role in mediating the function of Apc in hematopoiesis.

Cross-talk between YAP and RAR-RXR Drives Expression of Stemness Genes to Promote 5-FU Resistance and Self-Renewal in Colorectal Cancer Cells.

The mechanisms whereby the Hippo pathway effector YAP regulates cancer cell stemness, plasticity, and chemoresistance are not fully understood. We previously showed that in 5-fluorouracil (5-FU)-resistant colorectal cancer cells, the transcriptional coactivator YAP is differentially regulated at critical transitions connected with reversible quiescence/dormancy to promote metastasis. Here, we found that experimental YAP activation in 5-FU-sensitive and 5-FU-resistant HT29 colorectal cancer cells enhanced nuclear YAP localization and the transcript levels of the retinoic acid (RA) receptors RARα/γ and RAR target genes CYP26A1, ALDH1A3, and LGR5 through RA Response Elements (RARE). In these two cell models, constitutive YAP activation reinforced the expression of the stemness biomarkers and regulators ALDH1A3, LGR5, and OCT4. Conversely, YAP silencing, RAR/RXR inhibition by the pan-RAR antagonist BMS493, and vitamin A depletion downregulated stemness traits and self-renewal. Regarding the mechanisms engaged, proximity-dependent labeling, nuclear YAP pulldown coupled with mass spectrometry, and chromatin immunoprecipitation (ChIP)/re-ChIP experiments revealed: (i) the nuclear colocalization/interaction of YAP with RARγ and RXRs; and (ii) combined genomic co-occupancy of YAP, RARα/γ, and RXRα interactomes at proximal RAREs of LGR5 and ALDH1A3 promoters. Moreover, activation of the YAP/RAR-RXR cross-talk in colorectal cancer cells promoted RAR self-activation loops via vitamin A metabolism, RA, and active RAR ligands generated by ALDH1A3. Together, our data identify YAP as a bona fide RAR-RXR transcriptional coactivator that acts through RARE-activated stemness genes. IMPLICATIONS: Targeting the newly identified YAP/RAR-RXR cross-talk implicated in cancer cell stemness maintenance may lead to multitarget combination therapies for patients with colorectal cancer.