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Results for “stem cell model of development”

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At least 325 records · Page 18Linked to original sources
PubMed1999

A mechanism-based pharmacokinetic-enzyme model for cyclophosphamide autoinduction in breast cancer patients.

AIMS: This study investigated the pharmacokinetics of cyclophosphamide (CP) and its main metabolite 4-hydroxycyclophosphamide (4-OH-CP) in patients with breast cancer undergoing high dose chemotherapy prior to autologous stem cell transplantation. An enzyme turn-over model was also developed to study the time course of cyclophosphamide induction. METHODS: Fourteen patients received a combination of CP (6 g m-2 ), thiotepum (500 mg m-2 ) and carboplatin (800 mg m-2 ) as a 96 h infusion. Plasma concentrations of CP and 4-OH-CP were determined with h.p.l.c. and a pharmacokinetic and enzyme turn-over model applied to data using NONMEM. RESULTS: CP plasma concentrations were described by a two-compartment model with a noninducible and an inducible pathway, the latter forming 4-OH-CP. In the final enzyme model, CP affects the amount of enzymes by increasing the enzyme production rate. CP concentrations decreased during the infusion with no subsequent change in 4-OH-CP concentrations. CP inducible and noninducible clearance were estimated to 1.76 l h-1 (90% C.I. 0.92-2.58) and 1.14 l h-1 (0.31-1.85), respectively. The induction resulted in an approximately doubled CP clearance through the inducible pathway at the end of treatment. The model predicted the enzyme turn-over half-life to be 24 h. CONCLUSIONS: The presented mechanism-based enzyme induction model where the pharmacokinetics of the inducer and the enzyme pool counterbalance each other successfully described CP autoinduction. It is reasonable to believe that CP affects its own elimination by increasing the enzyme production rate and thereby increasing the amount of enzyme by which CP is eliminated.

Adult↗
PubMed1998

Overexpression of HOX11 leads to the immortalization of embryonic precursors with both primitive and definitive hematopoietic potential.

Primitive and definitive erythropoiesis represent distinct hematopoietic programs that differ with respect to stage of development, transcriptional control, and growth regulation. Although these differences have been recognized for some time, the relationship of the two erythroid lineages to each other is not well established. We have used a model system based on the hematopoietic development of embryonic stem (ES) cells in culture to investigate the origins of the earliest hematopoietic populations. Using ES cells transduced with a retrovirus that overexpresses the HOX11 gene, we have established factor-dependent hematopoietic cell lines that represent novel stages of embryonic hematopoiesis. Analysis of three of these cell lines indicates that they differ with respect to cytokine responsiveness, cell surface markers, and developmental potential. Two of the cell lines, EBHX1 and EBHX11, display the unique capacity to generate both primitive and definitive erythroid progeny as defined by morphology and expression of betaH1 and betamajor globin. The third line, EBHX14, has definitive erythroid and myeloid potential, but is unable to generate cells of the primitive erythroid lineage. Analysis of the cytokine responsiveness of the two lines with primitive erythroid potential has indicated that exposure to leukemia inhibitory factor (LIF) results in the upregulation of betaH1 and a change in cellular morphology to that of primitive erythrocytes. These findings are the first demonstration of a clonal cell line with primitive and definitive hematopoietic potential and support the interpretation that these lineages may arise from a common precursor in embryonic life. In addition, they suggest that LIF could play a role in the regulation of primitive erythropoiesis.

Animals↗
PubMed2004

Cancer stem cell biology: from leukemia to solid tumors.

The biology of stem cells and their intrinsic properties are now recognized as integral to tumor pathogenesis in several types of cancer. This observation has broad ramifications in the cancer research field and is likely to impact our understanding of the basic mechanisms of tumor formation and the strategies we use to treat cancers. A role for stem cells has been demonstrated for cancers of the hematopoietic system, breast and brain. Going forward it is likely that stem cells will also be implicated in other malignancies. Hence, a detailed understanding of stem cells and how they mediate tumor pathogenesis will be critical in developing more effective cancer therapies.

Animals↗
PubMed2004

Modeled microgravity inhibits osteogenic differentiation of human mesenchymal stem cells and increases adipogenesis.

Space flight-induced bone loss has been attributed to a decrease in osteoblast function, without a significant change in bone resorption. To determine the effect of microgravity (MG) on bone, we used the Rotary Cell Culture System [developed by the National Aeronautics and Space Administration (NASA)] to model MG. Cultured mouse calvariae demonstrated a 3-fold decrease in alkaline phosphatase (ALP) activity and failed to mineralize after 7 d of MG. ALP and osteocalcin gene expression were also decreased. To determine the effects of MG on osteoblastogenesis, we cultured human mesenchymal stem cells (hMSC) on plastic microcarriers, and osteogenic differentiation was induced immediately before the initiation of modeled MG. A marked suppression of hMSC differentiation into osteoblasts was observed because the cells failed to express ALP, collagen 1, and osteonectin. The expression of runt-related transcription factor 2 was also inhibited. Interestingly, we found that peroxisome proliferator-activated receptor gamma (PPARgamma2), which is known to be important for adipocyte differentiation, adipsin, leptin, and glucose transporter-4 are highly expressed in response to MG. These changes were not corrected after 35 d of readaptation to normal gravity. In addition, MG decreased ERK- and increased p38-phosphorylation. These pathways are known to regulate the activity of runt-related transcription factor 2 and PPARgamma2, respectively. Taken together, our findings indicate that modeled MG inhibits the osteoblastic differentiation of hMSC and induces the development of an adipocytic lineage phenotype. This work will increase understanding and aid in the prevention of bone loss, not only in MG but also potentially in age-and disuse-related osteoporosis.

Adipocytes↗
PubMed2000

Stem cell research: biology, ethics, and policy.

Human stem cell research may have many promising benefits, including giving us the ability to regenerate human tissue and organs, understand the process of early human development, and provide better models to test new drugs. However, it is very controversial and in many cases presently illegal because stem cells may be derived from human embryos or from a cloning process. This paper outlines the various techniques which may be used for deriving stem cells, the ethical problems such research presents, and suggestions for creating policy for human stem cells research.

Aborted Fetus↗
PubMed2003

Stem cells to tissue: molecular, cellular and anatomical heterogeneity in skeletal muscle.

Multiple waves of muscle precursors are released from skeletal muscle progenitor cells throughout developmental life, and this process is initiated in precise locations in the embryo. Skeletal muscle diversifies not only after the acquisition of muscle identity, but curiously heterogeneity is observed even in the stem cell population. Recent studies on cell lineage, cell fusion and the nature of post-natal satellite cells have expanded on our fundamental knowledge of the formation of this tissue, and how this tissue is replenished by resident and circulating regenerative stem cells during adult life.

Animals↗
PubMed2005

Systems-level dissection of the cell-cycle oscillator: bypassing positive feedback produces damped oscillations.

The cell-cycle oscillator includes an essential negative-feedback loop: Cdc2 activates the anaphase-promoting complex (APC), which leads to cyclin destruction and Cdc2 inactivation. Under some circumstances, a negative-feedback loop is sufficient to generate sustained oscillations. However, the Cdc2/APC system also includes positive-feedback loops, whose functional importance we now assess. We show that short-circuiting positive feedback makes the oscillations in Cdc2 activity faster, less temporally abrupt, and damped. This compromises the activation of cyclin destruction and interferes with mitotic exit and DNA replication. This work demonstrates a systems-level role for positive-feedback loops in the embryonic cell cycle and provides an example of how oscillations can emerge out of combinations of subcircuits whose individual behaviors are not oscillatory. This work also underscores the fundamental similarity of cell-cycle oscillations in embryos to repetitive action potentials in pacemaker neurons, with both systems relying on a combination of negative and positive-feedback loops.

Anaphase-Promoting Complex-Cyclosome↗
PubMed2006

Neural subtype specification from embryonic stem cells.

One of the keys to using embryonic stem cells (ESCs) in brain research and potential application in neurological diseases is directed differentiation of neuronal and glial subtypes. This may be achieved by application of developmental principles in guiding cell lineage specification from naïve stem cells. Establishment of defined ESC differentiation models that recapitulate in vivo development, especially from human ESCs, will most likely provide a dynamic tool for dissecting molecular mechanisms underlying early embryonic development that is otherwise not readily obtainable. This is also a rational and realistic way of producing enriched populations of functional neurons and glia for pathological analyses as well as possible therapeutic applications.

Animals↗
PubMed2003

Mouse and human embryonic stem cell models of hematopoiesis: past, present, and future.

Human embryonic stem (ES) cells provide a unique model and an important resource to analyze early hematopoietic development. Other systems to study mammalian hematopoiesis include mouse ES cells, dissection of timed mouse embryos, or use of human postnatal hematopoietic tissue typically isolated from bone marrow or umbilical cord blood. All these models have particular strengths and weaknesses. The extensive studies on murine hematopoiesis provide a basis for work on the human developmental system. Since there are likely some important species differences, use of human ES cells now provides an optimal means to evaluate basic cellular and molecular mechanisms that regulate the beginning stages of human blood development, prior to derivation of hematopoietic stem cells (HSCs). Eventually, research on human ES cells may provide an alternative source of HSCs and other blood products for hematopoietic cell transplantation or other cellular therapies.

Animals↗
PubMed2026

Altered ECM deposition and cell adhesion signaling in a human cortical organoid model of fragile X syndrome.

Fragile X Syndrome (FXS) is the most common inherited intellectual disability, and the most common monogenic cause of autism spectrum disorder (ASD). It is caused by epigenetic silencing of the FMR1 gene leading to the loss of FMRP, an RNA-binding protein that regulates local mRNA translation in neuronal dendrites, crucial for synapse development. Three-dimensional (3D) brain organoid models derived through in vitro differentiation of pluripotent stem cells offer a powerful tool to dissect the underlying mechanisms of neurodevelopmental disorders. Here, we generated human FXS and control organoids using isogenic human embryonic stem cell clones with and without the FXS mutation. Our results show that mature FXS cortical brain organoids can be derived by inhibiting the TGFβ and Wnt pathways. Moreover, expression analyses including immunofluorescence, qRT-PCR, proteomics and western blotting reveal altered levels of neuronal markers and ECM deposition along with modulated downstream signaling molecules. Interestingly, in silico analysis of proteomics revealed several altered pathways, such as cell adhesion, regulation of neurogenesis and cell cycle that are implicated in FXS. Collectively, our unique FXS-organoids derived from isogenic hESC lines may serve as a model for studying the pathology of FXS disorder and for developing therapeutical intervention.

Humans↗
PubMed2003

Assessment of the ultrastructural and proliferative properties of human embryonic stem cell-derived cardiomyocytes.

Assessment of early ultrastructural development and cell-cycle regulation in human cardiac tissue is significantly hampered by the lack of a suitable in vitro model. Here we describe the possible utilization of human embryonic stem cell (ES) lines for investigation of these processes. With the use of the embryoid body (EB) differentiation system, human ES cell-derived cardiomyocytes at different developmental stages were isolated and their histomorphometric, ultrastructural, and proliferative properties were characterized. Histomorphometric analysis revealed an increase in cell length, area, and length-to-width ratio in late-stage EBs (>35 days) compared with early (10-21 days) and intermediate (21-35 days) stages. This was coupled with a progressive ultrastructural development from an irregular myofibrillar distribution to an organized sarcomeric pattern. Cardiomyocyte proliferation, assessed by double labeling with cardiac-specific antibodies and either [3H]thymidine incorporation or Ki-67 immunolabeling, demonstrated a gradual withdrawal from cell cycle. Hence, the percentage of positively stained nuclei in early-stage cardiomyocytes ([3H]thymidine: 60 +/- 10%, Ki-67: 54 +/- 23%) decreased to 36 +/- 7% and 9 +/- 16% in intermediate-stage EBs and to <1% in late-stage cardiomyocytes. In conclusion, a reproducible temporal pattern of early cardiomyocyte proliferation, cell-cycle withdrawal, and ultrastructural maturation was noted in this model. Establishment of this unique in vitro surrogate system may allow to examine the molecular mechanisms underlying these processes and to assess interventions aiming to modify these properties. Moreover, the detailed characterization of the ES cell-derived cardiomyocyte may be crucial for the development of future cell replacement strategies aiming to regenerate functional myocardium.

Cell Differentiation↗
PubMed2004

Dnmt1 deficiency leads to enhanced microsatellite instability in mouse embryonic stem cells.

DNA hypomethylation is frequently seen in cancer and imparts genomic instability in mouse models and some tissue culture systems. However, the effects of genomic DNA hypomethylation on mutation rates are still elusive. We have developed a model system to analyze the effects of DNA methyltransferase 1 (Dnmt1) deficiency on DNA mismatch repair (MMR) in mouse embryonic stem (ES) cells. We generated sibling ES cell clones with and without functional Dnmt1 expression, containing a stable reporter gene that allowed us to measure the slippage rate at a mononucleotide repeat. We found that Dnmt1 deficiency led to a 7-fold increase in the microsatellite slippage rate. Interestingly, the region flanking the mononucleotide repeat was unmethylated regardless of Dnmt1 status, suggesting that it is not the local levels of DNA methylation that direct the increase in microsatellite instability (MSI). The enhanced MSI was associated with higher levels of histone H3 acetylation and lower MeCP2 binding at regions near the assayed microsatellite, suggesting that Dnmt1 loss may decrease MMR efficiency by modifying chromatin structure.

Animals↗
PubMed2004

Corneal development, limbal stem cell function, and corneal epithelial cell migration in the Pax6(+/-) mouse.

PURPOSE: To investigate the etiology of corneal dysfunction in the Pax6(+/-) mouse model of aniridia-related keratopathy. METHODS: Mosaic patterns of X-gal staining were compared in the corneal and limbal epithelia of female Pax6(+/-) and Pax6(+/+) littermates, age 3 to 28 weeks, hemizygous for an X-linked LacZ transgene, and Pax6(+/+), LacZ(-)<-->Pax6(+/+), LacZ(+) and Pax6(+/+), LacZ(-)<-->Pax6(+/-), LacZ(+) chimeras. Histologic examination of chimeric corneas was performed. RESULTS: Disrupted patterns of X-gal staining showed that heterozygosity for Pax6 perturbed clonal patterns of growth and development in the corneal and limbal epithelium. Centripetal migration of Pax6(+/-) corneal epithelial cells was diverted. Normal patterns of centripetal Pax6(+/-) cell migration and epithelial morphology were restored in Pax6(+/+)<-->Pax6(+/-) chimeras. Fewer, larger clones of limbal stem cells were present in Pax6(+/-) eyes, compared with wild-type. In the chimeras, Pax6(+/-) limbal stem cells were cell-autonomously depleted or less efficient than wild-type cells at producing progeny to populate the corneal epithelium. CONCLUSIONS: The correct Pax6 dosage is necessary for normal clonal growth during corneal development, normal limbal stem cell activity, and correct corneal epithelial cell migration. Disruption of normal cell movement in heterozygotes may be the consequence of failure of nonautonomous guidance cues. Degeneration of the corneal surface in aniridia-related keratopathy relates to both a deficiency within the limbal stem cell niche and nonautonomous diversion of corneal epithelial cell migration.

Animals↗
PubMed1985

Malignant fibrous histiocytoma in rats at sites of implanted millipore filters.

Soft-tissue tumors developing in rats at the site of implanted Millipore filters showed the structural, cytochemical, and biologic characteristics of the malignant fibrous histiocytomas occurring in man. Evidence from this tumor model suggests that malignant fibrous histiocytomas can arise from pluripotential mesenchymal stem cells which are not derived from the mononuclear/phagocytic system and that chronic inflammation and scarring may predispose to their development.

Animals↗
PubMed2004

Pretumor progression: clonal evolution of human stem cell populations.

Multistep carcinogenesis through sequential cycles of mutation and clonal succession is usually described as tumor progression, or the clonal evolution of tumor cell populations. However, many mutations found in cancers are also compatible with normal appearing phenotypes and therefore genetic progression may precede tumor progression. To better characterize such pretumor progression (mutations in the absence of visible phenotypic changes), a quantitative model was developed that postulates most oncogenic cancer mutations first accumulate in normal appearing colon crypt niche stem cells. Each crypt contains multiple stem cells, and random niche stem cell loss with replacement eventually leads to the loss of all stem cell lineages except one. This niche succession or crypt clonal evolution is similar to the clonal succession of tumor progression except it does not require selection or change visible phenotype. Mutations may sequentially accumulate during stem cell clonal evolution either through drift (passenger mutations) or selection. To determine the feasibility of pretumor progression, mutation rates sufficient to recreate the epidemiology of colorectal cancer were estimated. Pretumor progression may completely substitute for visible tumor progression because it is theoretically possible for all cancer mutations to first accumulate in normal appearing colon with normal replication fidelity. Elevated mutation rates or tumorigenesis may be unnecessary for early progression.

Adult↗
PubMed2005

A germ cell origin of embryonic stem cells?

Because embryonic stem (ES) cells are generally derived by the culture of inner cell mass (ICM) cells, they are often assumed to be the equivalent of ICM cells. However, various evidence indicates that ICM cells transition to a different cell type during ES-cell derivation. Historically, ES cells have been believed to most closely resemble pluripotent primitive ectoderm cells derived directly from the ICM. However, differences between ES cells and primitive ectoderm cells have caused developmental biologists to question whether ES cells really have an in vivo equivalent, or whether their properties merely reflect their tissue culture environment. Here, we review recent evidence that the closest in vivo equivalent of an ES cell is an early germ cell.

Animals↗
PubMed1994

Cloning and characterization of the mouse XPAC gene.

Xeroderma Pigmentosum is a human disease, which is, among others, characterized by a high incidence of (sunlight induced) skin cancer, due to a defect in nucleotide excision repair (NER). The human DNA repair gene XPAC corrects this defect in cells isolated from Xeroderma Pigmentosum complementation group A (XP-A) patients. To enable the development of a transgenic mouse model for XP-A by gene targeting in embryonic stem cells, we cloned and characterized the mouse homologue of the XPAC gene. The mouse XPAC gene was found to consist of 6 exons, spanning approximately 21 kb. The nucleotide sequence of the exons is identical to that of the also cloned the mouse XPAC cDNA. Furthermore, the deduced amino acid sequence of the XPAC protein is the same as the one published previously by Tanaka et al. From CAT assay analysis, the promoter of the XPAC gene appeared to be located within 313 bp upstream of the assumed transcriptional start site. Like the promoters of other eukaryotic DNA repair genes (i.e. ERCC-1 and XPBC/ERCC-3), the mouse XPAC promoter region lacks classical promoter elements like TATA-, GC- and CAAT boxes. However, it contains an unique polypyrimidine-rich box, which is so far only found in genes encoding DNA repair enzymes. The function of this box in the regulation of transcription is still unclear.

Animals↗