Maintain Stem Cell Populations Research Articles

Overview of the molecular mechanisms of migration and invasion in glioblastoma multiforme.

Glioblastoma (GBM) is one of the most devastating cancers, with an approximate median survival of only 16 months. Although some new insights into the fantastic heterogeneity of this kind of brain tumor have been revealed in recent studies, all subclasses of GBM still demonstrate highly aggressive invasion properties to the surrounding parenchyma. This behavior has become the main obstruction to current curative therapies as invasive GBM cells migrate away from these foci after surgical therapies. Therefore, this review aimed to provide a relatively comprehensive study of GBM invasion mechanisms, which contains an intricate network of interactions and signaling pathways with the extracellular matrix (ECM). Among these related molecules, TGF-β, the ECM, Akt, and microRNAs are most significant in terms of cellular procedures related to GBM motility and invasion. Moreover, we also review data indicating that Musashi-1 (MSI1), a neural RNA-binding protein (RBP), regulates GBM motility and invasion, maintains stem cell populations in GBM, and promotes drug-resistant GBM phenotypes by stimulating necessary oncogenic signaling pathways through binding and regulating mRNA stability. Importantly, these necessary oncogenic signaling pathways have a close connection with TGF-β, ECM, and Akt. Thus, it appears promising to find MSI-specific inhibitors or RNA interference-based treatments to prevent the actions of these molecules despite using RBPs, which are known as hard therapeutic targets. In summary, this review aims to provide a better understanding of these signaling pathways to help in developing novel therapeutic approaches with better outcomes in preclinical studies.

BMP signalling is required for extra-embryonic ectoderm development during pre-to-post-implantation transition of the mouse embryo

At implantation, the mouse embryo undergoes a critical transformation which requires the precise spatiotemporal control of signalling pathways necessary for morphogenesis and developmental progression. The role played by such signalling pathways during this transition are largely unexplored, due to the inaccessibility of the embryo during the implantation when it becomes engulfed by uterine tissues. Genetic studies demonstrate that mutant embryos for BMPs die around gastrulation. Here we have aimed to dissect the role of BMPs during pre-to post-implantation transition by using a protocol permitting the development of the embryo beyond implantation stages in vitro and using stem cells to mimic post-implantation tissue organisation. By assessing both the canonical and non-canonical mechanisms of BMP, we show that the loss of canonical BMP activity compromises the extra-embryonic ectoderm development. Our analyses demonstrate that BMP signalling maintains stem cell populations within both embryonic/extra-embryonic tissues during pre-to post-implantation development. These results may provide insight into the role played by BMP signalling in controlling early embryogenesis.

Opioids Impair Intestinal Epithelial Repair in HIV-Infected Humanized Mice.

Intestinal barrier dysfunction and subsequent microbial translocation play crucial roles in persistent immune activation leading to HIV disease progression. Opioid use is associated with worse outcome in HIV-infected patients. The exacerbated disease progression by opioids is mainly driven by excessive intestinal inflammation and increased gut permeability. The objective of this study is to investigate how opioids potentiate HIV disease progression by compromising intestinal barrier function and impairing intestinal epithelial self-repair mechanism. In the present study, abnormal intestinal morphology and reduced epithelial proliferation were observed in bone marrow-liver-thymus humanized mice and in HIV-infected patients who were exposed to opioids. In bone marrow-liver-thymus mice, HIV, and morphine independently, and additively induced gut dysbiosis, especially depletion of Lachnospiraceae, Ruminococcaceae, and Muribaculaceae. We also observed that the abundance of Lachnospiraceae, Ruminococcaceae, and Muribaculaceae negatively correlated with apoptosis of epithelial cells, and intestinal IL-6 levels. Previous studies have shown that these bacterial families play crucial roles in maintaining intestinal homeostasis because they include most short-chain fatty acid-producing members. Short-chain fatty acids have been shown to maintain stem cell populations and suppress inflammation in the gut by inhibiting histone deacetylases (HDAC). In addition, we demonstrate that morphine exposure inhibited growth of intestinal organoids derived from HIV transgenic mice by suppressing Notch signaling in an HDAC-dependent manner. These studies implicate an important role for HDAC in intestinal homeostasis and supports HDAC modulation as a therapeutic intervention in improving care of HIV patients, especially in opioid-abusing population.

Retinoic Acid Is Required for Neural Stem and Progenitor Cell Proliferation in the Adult Hippocampus.

SummaryNeural stem and precursor cell (NSPC) proliferation in the rodent adult hippocampus is essential to maintain stem cell populations and produce new neurons. Retinoic acid (RA) signaling is implicated in regulation of adult hippocampal neurogenesis, but its exact role in control of NSPC behavior has not been examined. We show RA signaling in all hippocampal NSPC subtypes and that inhibition of RA synthesis or signaling significantly decreases NSPC proliferation via abrogation of cell-cycle kinetics and cell-cycle regulators. RA signaling controls NSPC proliferation through hypoxia inducible factor-1α (HIF1α), where stabilization of HIF1α concurrent with disruption of RA signaling can prevent NSPC defects. These studies demonstrate a cell-autonomous role for RA signaling in hippocampal NSPCs that substantially broadens RA's function beyond its well-described role in neuronal differentiation.

Genetic Insights Into Frailty: Association of 9p21-23 Locus With Frailty.

Frailty is a complex aging phenotype associated with increased vulnerability to disability and death. Understanding the biological antecedents of frailty may provide clues to healthy aging. The genome-wide association study hotspot, 9p21-23 region, is a risk locus for a number of age-related complex disorders associated with frailty. Hence, we conducted an association study to examine whether variations in 9p21-23 locus plays a role in the pathogenesis of frailty in 637 community-dwelling Ashkenazi Jewish adults aged 65 and older enrolled in the LonGenity study. The strongest association with frailty (adjusted for age and gender) was found with the SNP rs518054 (odds ratio: 1.635, 95% CI = 1.241–2.154; p-value: 4.81 × 10−04) intergenic and located between LOC105375977 and C9orf146. The prevalence of four SNPs (rs1324192, rs7019262, rs518054, and rs571221) risk alleles haplotype in this region was significantly higher (compared with other haplotypes) in frail older adults compared with non-frail older adults (29.7 vs. 20.8%, p = 0.0005, respectively). Functional analyses using in silico approaches placed rs518054 in the CTCF binding site as well as DNase hypersensitive region. Furthermore, rs518054 was found to be in an enhancer site of NFIB gene located downstream. NFIB is a transcription factor that promotes cell differentiation during development, has antiapoptotic effect, maintains stem cell populations in adult tissues, and also acts as epigenetic regulators. Our study found novel association of SNPs in the regulatory region in the 9p21-23 region with the frailty phenotype; signifying the importance of this locus in aging.

Hedgehog and Vitamin D Signaling Pathways in Development and Disease.

The classic physiological activity associated with the vitamin D scaffold is the maintenance of calcium and phosphorous homeostasis in the bone. This activity is commonly attributed to direct binding of 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3, calcitriol], the hormonally active form of vitamin D, to the vitamin D receptor (VDR). More recently, calcitriol and VDR have been shown to control the expression of genes associated with cellular proliferation and differentiation in a wide variety of cells, suggesting more extensive biological activities for the vitamin D system. Recently, calcitriol and several structurally related members of the vitamin D class of seco-steroids have demonstrated the ability to regulate the hedgehog (Hh) signaling pathway. Hh signaling plays an essential role with respect to tissue differentiation during embryogenesis and maintains stem cell populations in certain adult tissues. Potential mechanisms of cross talk between the two signaling pathways highlight our evolving understanding of the complexities of calcitriol/VDR signaling and suggest a cooperative role during multiple stages of human development and disease.

Periodontal Stem Cells: a Historical Background and Current Perspectives

In this review we discuss the historical perspective of stem cell populations from oral tissues in light of our current understanding of stem cell biology. Stem cells and their niches have been identified in the periodontium starting from the late 1970s. Applying new criteria for the identification and characterization reveals that oral tissues comprise a multipotent primitive neural crest-like stem cell population capable of differentiating into neural crest derived cell lineages of the cranial-facial zone. This population supplies cells to a more restricted stem cell type with tissue specific epigenetic memory that differentiates into cell lineages characteristic of their tissue origin. We believe that the microenvironment plays an essential role in maintaining stem cell populations and directing their migration and differentiation, and that this factor needs to be considered for utilization of stem cell-based therapy for periodontal regeneration and regenerative dental medicine.

Abstract B59: Polycomb group ring finger protein plays a role in gamma ionizing radiation-induced DNA damage response in MCF7 cell line.

Abstract Polycomb group (PcG) gene product is a family of proteins that were accumulated with complexes in nuclear and plays an important role in development and maintaining stem cell population of hematopoietic and neuronal cell lineages. PcG complexes can regulate the transcriptional activity of many genes by epigenetic silencing involved in embryogenesis. Recent reports showed the overexpressions of PcG proteins were correlated with the severity of many cancers. To investigate the underlying mechanisms of PcG ubiquitin ligase (PCGF1-6) on DNA damage response after exposure to gamma ionizing radiation, we generated the stable knockdown MCF7 breast cancer cell lines capable of silencing each of PcG ubiquitin ligase genes. Cell survival and proliferation analysis in stable PcG ubiquitin ligase knockdown MCF7 cell lines was compared to the analysis in control MCF7 cell lines after treatment of gamma ionizing radiation using MTT and colony forming assay. Furthermore, we found that loss of several PcG ubiquitin ligases sensitizes MCF7 cell lines to gamma ionizing radiation-mediated growth inhibition. We further demonstrate that several PCGF PcG ubiquitin ligases are localized at γ-H2AX foci after treatment of gamma ionizing radiation. These results demonstrate that PCGF family can coordinately regulate the cell resistance mechanism in DNA damage response. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B59.

Identification of an Aurora-A/PinsLINKER/ Dlg Spindle Orientation Pathway using Induced Cell Polarity in S2 Cells

Asymmetric cell division is intensely studied because it can generate cellular diversity as well as maintain stem cell populations. Asymmetric cell division requires mitotic spindle alignment with intrinsic or extrinsic polarity cues, but mechanistic detail of this process is lacking. Here, we develop a method to construct cortical polarity in a normally unpolarized cell line and use this method to characterize Partner of Inscuteable (Pins; LGN/AGS3 in mammals) -dependent spindle orientation. We identify a previously unrecognized evolutionarily conserved Pins domain (Pins(LINKER)) that requires Aurora-A phosphorylation to recruit Discs large (Dlg; PSD-95/hDlg in mammals) and promote partial spindle orientation. The well-characterized Pins(TPR) domain has no function alone, but placing the Pins(TPR) in cis to the Pins(LINKER) gives dynein-dependent precise spindle orientation. This "induced cortical polarity" assay is suitable for rapid identification of the proteins, domains, and amino acids regulating spindle orientation or cell polarity.

Identification of a polymorphism in the RING finger of human Bmi-1 that causes its degradation by the ubiquitin–proteasome system

Bmi-1 is a polycomb protein that plays an important role in tumor cell development and maintaining stem cell populations of many cell lineages. Here we identify a polymorphism in human Bmi-1 that changes a cysteine within its RING domain to tyrosine. This C18Y polymorphism is associated with a significant decrease in Bmi-1 level and its elevated ubiquitination, suggesting that it is being destroyed by the ubiquitin–proteasome system. Consistent with this, treating cells with the proteasome inhibitor MG-132 significantly increases C18Y Bmi-1 levels. This is the first example of a polymorphism in Bmi-1 that reduces levels of this important protein. Structured summary MINT- 6948574: Bmi-1 (uniprotkb: P35226) physically interacts (MI: 0218) with Ubiquitin (uniprotkb: P62988) by anti tag coimmunoprecipitation (MI: 0007)

Arabidopsis CLV3 Peptide Directly Binds CLV1 Ectodomain

CLV1, which encodes a leucine-rich repeat receptor kinase, and CLV3, which encodes a secreted peptide, function in the same genetic pathway to maintain stem cell populations in Arabidopsis shoot apical meristem. Here, we show biochemical evidence, by ligand binding assay and photoaffinity labeling, that the CLV3 peptide directly binds the CLV1 ectodomain with a dissociation constant of 17.5 nM. The CLV1 ectodomain also interacts with the structurally related CLE peptides, with distinct affinities depending on the specific amino acid sequence. Our results provide direct evidence that CLV3 and CLV1 function as a ligand-receptor pair involved in stem cell maintenance.

Stem/progenitor cells in amphibian limb and spinal cord regeneration

Amphibian regeneration may replace tissue via homotypic cells, dedifferentiation, transdifferentiation or stem cells. The mechanism may vary with life cycle stage. Expression of Notch signaling components suggests a role for stem cells. We examine the role of stem cells in regeneration-competent and incompetent stages of Xenopus laevis (clawed frog) tadpoles, juvenile and adult axolotls (the Mexican salamander Ambystoma mexicanum) and the regeneration-deficient axolotl mutant short-toes. Notch1 signaling is a key pathway in maintaining stem cell populations. The stem cell marker Musashi (Msi) is an RNA-binding protein inhibiting translation of Numb to maintain Notch1 signaling. Isoforms of Msi1 and Msi2 are expressed in temporal and spatial patterns that correlate with regeneration behavior. Msi-1 is expressed in specific tissue compartments in regeneration-competent Xenopus limb and spinal cord and decreases in incompetent tadpole and adult Xenopus tissues. Msi2 isoforms change between competent and incompetent Xenopus stages. Rapidly growing juvenile axolotls show high levels of Msi1 in both cord and limb, while intact adult axolotl tissues shows low levels of Msi1 that are upregulated following injury. Msi expression is also lost in limbs of the axolotl limb regeneration mutant short-toes, but maintained in the regeneration competent mutant spinal cord. Support: Indiana 21st Century Research and Technology Fund ; W.M. Keck Foundation.

Hedgehog signalling in skin development and cancer

Basal cell carcinoma (BCC) is the most common human malignancy, affecting 750,000 Americans each year. The understanding of mutations that are known to activate hedgehog (Hh) signalling pathway genes, including PATCHED (PTCH), sonic hedgehog (Shh) and smoothened (Smo), has substantially expanded our current understanding of the genetic basis of BCC development. The Hh signalling pathway is one of the most fundamental signal transduction pathways in embryonic development. In skin, the Shh pathway is crucial for maintaining stem cell population, and for regulating hair follicle and sebaceous gland development. This pathway plays a minimal role in adult tissues, but is known to be activated in many neoplasms, including those arising in the skin. In this review, we attempt to summarize the results of published studies on some important aspects of the Shh pathway and its involvement in skin development and carcinogenesis. We also provide a description of various animal models that have been developed, based on our knowledge of the Shh pathway in human skin cancers. Additionally, we include a brief description of studies conducted in our laboratory and by others on the chemoprevention of BCCs. This review therefore provides a current understanding of the role of the Shh pathway in skin development and neoplasia. It also provides a basis for the molecular target-based chemoprevention and therapeutic management of skin cancer.

Stem Cell Signalling Networks in Plants

The essential nature of meristematic tissues is addressed with reference to conceptual frameworks that have been developed to explain the behaviour of animal stem cells. Comparisons are made between different types of plant meristems with the objective of highlighting common themes that might illuminate underlying mechanisms. A more in depth comparison of the root and shoot apical meristems is made which suggests a common mechanism for maintaining stem cells. The relevance of organogenesis to stem cell maintenance is discussed, along with the nature of underlying mechanisms which help ensure that stem cell production is balanced with the depletion of cells through differentiation. Mechanisms that integrate stem cell behaviour in the whole plant are considered, with a focus on the roles of auxin and cytokinin. The review concludes with a brief discussion of epigenetic mechanisms that act to stabilise and maintain stem cell populations.

The Hedgehog Signalling Pathway in the Gastrointestinal Tract: Implications for Development, Homeostasis, and Disease

The hedgehog signalling pathway is critical to normal mammalian gastrointestinal development. Through epithelial-mesenchymal interactions, hedgehog signalling ensures appropriate axial patterning of the embryonic gut. Congenital abnormalities, including malrotations, anorectal malformations, and tracheoesophageal fistula are associated with germ-line mutations/deletion of genes encoding hedgehog signalling components in man and present in genetically engineered animal models. In adults, there is evidence that the pathway plays a role in maintaining stem cell populations in the stomach and directing epithelial cell differentiation in the intestine. Recent data implicate hedgehog signalling in the formation and maintenance of a number of malignancies, including those of the upper gastrointestinal (GI) tract and pancreas, in which abrogation of the pathway offers a novel therapeutic approach in animal models. Most recently, evidence in vitro indicates that there is a recapitulation of embryonic hedgehog signalling in acute epithelial injury and chronic inflammation, a finding with key implications for inflammatory disorders of the intestine, such as inflammatory bowel diseases. This pathway may provide an important link between chronic inflammation and cancer. We summarize the available evidence demonstrating that this developmental pathway has continuing roles in adult homeostasis and is dysregulated in malignancy and inflammation of the gastrointestinal tract.

Wound Dressings Alter the Colony-Forming Efficiency of Keratinocytes in Cultured Sheet Grafts

Cultured keratinocyte grafts transplanted for skin wound repair are often affixed to a wound dressing to facilitate handling. In this study, the ability of five different types of wound dressings to support cell viability and maintain stem cell populations in the cultured grafts was determined. Postconfluent keratinocyte (NHK) sheets were attached to wound dressings for 24 h and then released by trypsinization. Cell viability was determined and NHKs were assessed for clonogenic capacity by colony-forming efficiency (CFE) assays. CFEs for NHKs exposed to a collagen-bonded, bilaminate membrane and a polyurethane film were significantly less than control. On the other hand, CFEs for NHKs exposed to a collagen/alginate dressing and to petrolatum-impregnated gauze were significantly greater than control. The choice of a wound dressing carrier has implications for maintaining long-term viability of the transplanted sheet of epithelium.

A Molecular Link between Stem Cell Regulation and Floral Patterning in Arabidopsis

The homeotic gene AGAMOUS (AG) has dual roles in specifying organ fate and limiting stem cell proliferation in Arabidopsis flowers. We show that the floral identity protein LEAFY (LFY), a transcription factor expressed throughout the flower, cooperates with the homeodomain protein WUSCHEL (WUS) to activate AG in the center of flowers. WUS was previously identified because of its role in maintaining stem cell populations in both shoot and floral meristems. The unsuspected additional role of WUS in regulating floral homeotic gene expression supports the hypothesis that floral patterning uses a general meristem patterning system that was present before flowers evolved. We also show that AG represses WUS at later stages of floral development, thus creating a negative feedback loop that is required for the determinate growth of floral meristems.

Defective epithelial chloride transport in a gene-targeted mouse model of cystic fibrosis : L.L. CLARKE ET AL. Science 257, 1125–1128

The homeotic gene AGAMOUS (AG) has dual roles in specifying organ fate and limiting stem cell proliferation in Arabidopsis flowers. We show that the floral identity protein LEAFY (LFY), a transcription factor expressed throughout the flower, cooperates with the homeodomain protein WUSCHEL (WUS) to activate AG in the center of flowers. WUS was previously identified because of its role in maintaining stem cell populations in both shoot and floral meristems. The unsuspected additional role of WUS in regulating floral homeotic gene expression supports the hypothesis that floral patterning uses a general meristem patterning system that was present before flowers evolved. We also show that AG represses WUS at later stages of floral development, thus creating a negative feedback loop that is required for the determinate growth of floral meristems.

Cystic fibrosis in the mouse by targeted insertional mutagenesis : J.R. DORIN ET AL. Nature 359, 211–215

The homeotic gene AGAMOUS (AG) has dual roles in specifying organ fate and limiting stem cell proliferation in Arabidopsis flowers. We show that the floral identity protein LEAFY (LFY), a transcription factor expressed throughout the flower, cooperates with the homeodomain protein WUSCHEL (WUS) to activate AG in the center of flowers. WUS was previously identified because of its role in maintaining stem cell populations in both shoot and floral meristems. The unsuspected additional role of WUS in regulating floral homeotic gene expression supports the hypothesis that floral patterning uses a general meristem patterning system that was present before flowers evolved. We also show that AG represses WUS at later stages of floral development, thus creating a negative feedback loop that is required for the determinate growth of floral meristems.