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Query: EC:2.7.10.1 (ERK)
 95,504 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Little is known about postnatal enteric nervous system (ENS) development, but some reports suggest that the postnatal bowel may contain neural stem cells. Therefore, we created an in vitro model of desegregation using an enzymatic and mechanical tissue technique. This approach yielded a group of cells from the small intestine of lactating and adult mice, which ex vivo attach to the culture dish; actively proliferate; and express nestin, vimentin, and the pro-neural transcription factors neurogenin-2 (ngn-2), Sox-10, and Mash-1. In the conditions grown, double immunostains suggest that they differentiate into various cell types, particularly neurons, smooth muscle, and glia including 04 protein-positive cells. They also express the neurotrophic-protein tyrosine kinase (Trk) receptors TrkA, TrkB, and TrkC; the low-affinity neurotrophin receptor p75NTR; and the glial-derived neurotrophic factor receptors (GFR)alpha-1, GFRalpha-2, and GFRalpha-3. The neurons expressed several sensory and motor neurotransmitters present in the central and enteric nervous systems, including calcitonin gene-related peptide, neuropeptideY, peptideYY, substance P, vasoactive intestinal polypeptide, and galanin; along with glia, these neurons formed elaborate intercellular connections. They also express c-KIT, CD34, CD20, and CD45RO, suggesting they either have a hematogenous origin or may differentiate toward hematogenous lines. These findings suggest that these cells may be enteric neural stem cells (ENSCs); may normally be present in the small intestine; and may have the capacity to proliferate and differentiate into neurons, glia, and smooth muscle. Further identification and purification of intestinal ENSCs will provide a means to study the regulation of their differentiation and should give insight into the mechanisms involved in development and remodeling of the ENS. The possible therapeutic application of postnatal stem cells such as ENSCs needs to be evaluated, including their use for transplantation in the central nervous system.
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PMID:Cultured nestin-positive cells from postnatal mouse small bowel differentiate ex vivo into neurons, glia, and smooth muscle. 1557 54

The non-angiogenic role of vascular endothelial growth factor (VEGF), and its receptors flt-1 and flk-1, together with downstream signaling pathways were examined in fetal and postnatal rat cerebral cortical organotypic explants. VEGF application in both paradigms caused a significant increase in astroglial proliferation and a dose-dependent increase in GFAP and nestin immunoreactivity. The VEGF receptor flt-1 was observed on most, though not all astrocytes, while flk-1 receptor immunoexpression was absent. Treatment with antisense oligonucleotides (AS-ODNs) to flt-1 resulted in a dramatic decrease in GFAP and nestin immunoreactivity, which further confirmed the role of flt-1 in mediating VEGF's gliotrophic effects, while AS-ODNs to flk-1 had no effect. VEGF-induced gliotrophic effects were found to be mediated by the MAPK/ERK and PI-3 kinase signaling pathways, since the both the MEK1 inhibitor, PD98059 and the PI-3 kinase inhibitor, Wortmannin abolished VEGF-induced astrocytic GFAP(+) expression. Although high dose VEGF application resulted in strong upregulation of both GFAP and nestin immunoreactivity in astrocytes, overlap of the two proteins was not observed in all cells, suggesting that some of the nestin(+) cells might be neural progenitors. Exposure to VEGF resulted in upregulation of both VEGF and bFGF mRNA at the one-day time point, and bFGF protein by 3 days; VEGF activated astrocytes expressed bFGF to a much greater degree than those in untreated explants. The increased expression of bFGF induced by VEGF, may serve in the proliferation of multipotential neural stem/progenitor cells in vitro. VEGF, an established angiogenic factor, appears to play a significant role in the growth and differentiation of astrocytes in the CNS.
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PMID:Astrocyte growth effects of vascular endothelial growth factor (VEGF) application to perinatal neocortical explants: receptor mediation and signal transduction pathways. 1575 57

Although traditionally recognized for maintaining extracellular matrix integrity during morphogenesis, the function of matrix metallo-proteinases (MMPs) and their inhibitors, the tissue inhibitors of metalloproteinases (TIMPs), in the mature nervous system is essentially unknown. Here, we report that TIMP-2 induces pheochromocytoma PC12 cell-cycle arrest via regulation of cell-cycle regulatory proteins, resulting in differentiation and neurite outgrowth. TIMP-2 decreases cyclins B and D expression and increases p21Cip expression. Furthermore, TIMP-2 promotes cell differentiation via activation of the cAMP/Rap1/ERK (extracellular signal-regulated kinase) pathway. Expression of dominant-negative Rap1 blocks TIMP-2-mediated neurite outgrowth. Both the cell-cycle arrest and neurite outgrowth induced by TIMP-2 was independent of MMP inhibitory activity. Consistent with the PC12 cell data, primary cultures of TIMP-2 knock-out cerebral cortical neurons exhibit significantly reduced neurite length, which is rescued by TIMP-2. These in vitro results were corroborated in vivo. TIMP-2 deletion causes a delay in neuronal differentiation, as demonstrated by the persistence of nestin-positive progenitors in the neocortical ventricular zone. The interaction of TIMP-2 with alpha3beta1 integrin in the cerebral cortex suggests that TIMP-2 promotes neuronal differentiation and maintains mitotic quiescence in an MMP-independent manner through integrin activation. The identification of molecules responsible for neuronal quiescence has significant implications for the ability of the adult brain to generate new neurons in response to injury and neurological disorders, such as Alzheimer's and Parkinson's diseases.
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PMID:Tissue inhibitor of metalloproteinase-2 promotes neuronal differentiation by acting as an anti-mitogenic signal. 1590 73

Epithelial metaplasia occurs when one predominant cell type in a tissue is replaced by another, and is frequently associated with an increased risk of subsequent neoplasia. In both mouse and human pancreas, acinar-to-ductal metaplasia has been implicated in the generation of cancer precursors. We show that pancreatic epithelial explants undergo spontaneous acinar-to-ductal metaplasia in response to EGFR signaling, and that this change in epithelial character is associated with the appearance of nestin-positive transitional cells. Lineage tracing involving Cre/lox-mediated genetic cell labeling reveals that acinar-to-ductal metaplasia represents a true transdifferentiation event, mediated by initial dedifferentiation of mature exocrine cells to generate a population of nestin-positive precursors, similar to those observed during early pancreatic development. These results demonstrate that a latent precursor potential resides within mature exocrine cells, and that this potential is regulated by EGF receptor signaling. In addition, these observations provide a novel example of rigorously documented transdifferentiation within mature mammalian epithelium, and suggest that plasticity of mature cell types may play a role in the generation of neoplastic precursors.
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PMID:Pancreatic epithelial plasticity mediated by acinar cell transdifferentiation and generation of nestin-positive intermediates. 1602 May 18

Cells from human amniotic fluid derived from the fetus are considered a source of multipotent cells. Their properties have not been fully exploited, partially because unlike other embryonic sources such as embryonic stem (ES) cells, cell lines from amniocentesis samples have not been generated. We have established and characterized the properties of eight individual cell lines. Flow cytometry using several cell surface markers showed that all cell lines generated consisted of homogeneous populations that lack HLAII antigenicity. Using a combination of immunocytochemistry, Western blotting, and RT-PCR, we found weak expression of Oct4 and nestin and strong expression of tubulin-betaIII, MAP2, and tau. Specific markers for cholinergic, (nor)adrenergic, and GABAergic neurons or glia were weakly expressed or absent, whereas expression of factors implicated in early induction of dopaminergic neurons, TGF-beta3 and beta-catenin were present. Further analysis showed strong expression of EN-1, c-RET, PTX3, and NURR1 essential for induction and survival of midbrain dopaminergic neurons, TH, AADC, and VMAT2 components of dopamine synthesis and secretion, and syntaxin1A and SNAP-25 necessary for neurotransmitter exocytosis. This phenotype was retained throughout passages and up to the current passage 36. Expression of neuronal and dopaminergic markers in individual AF cell lines was comparable to expression in neurons induced from ES cells and in IMR-32 and SH-SY5Y neuroblastomas. Our data show that cell lines can be derived from subcultures of amniocentesis, and are primarily composed of a population of progenitors with a phenotype similar to that of committed mesencephalic dopaminergic neurons.
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PMID:Stable expression of a neuronal dopaminergic progenitor phenotype in cell lines derived from human amniotic fluid cells. 1655 79

Nestin, an intermediate filament protein, is widely used as stem cell marker. Nestin has been shown to interact with other cytoskeleton proteins, suggesting a role in regulating cellular cytoskeletal structure. These studies examined renal nestin localization and developmental expression in mice. In developing kidney, anti-nestin antibody revealed strong immunoreactivity in vascular cleft of the S-shaped body and vascular tuft of capillary loop-stage glomerulus. The nestin-positive structures also were labeled by endothelial cell markers FLK1 and CD31 in immature glomeruli. Nestin was not detected in epithelial cells of immature glomeruli. In contrast, in mature glomerular, nestin immunoreactivity was observed only outside laminin-positive glomerular basement membrane, and co-localized with nephrin, consistent with podocyte nestin expression. In adult kidney, podocytes were the only cells that exhibited persistent nestin expression. Nestin was not detected in ureteric bud and its derivatives throughout renal development. Cell lineage studies, using a nestin promoter-driven Cre mouse and a ROSA26 reporter mouse, showed a strong beta-galactosidase activity in intermediate mesoderm in an embryonic day 10 embryo and all of the structures except those that were derived from ureteric bud in embryonic kidney through adult kidney. These studies show that nestin is expressed in progenitors of glomerular endothelial cells and renal progenitors that are derived from metanephric mesenchyme. In the adult kidney, nestin expression is restricted to differentiated podocytes, suggesting that nestin could play an important role in maintaining the structural integrity of the podocytes.
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PMID:Differential expression of the intermediate filament protein nestin during renal development and its localization in adult podocytes. 1657 84

Glucagon-like peptide-1 (GLP-1) is an insulinotropic hormone expressed by alternative post-translational processing of proglucagon in the intestines, endocrine pancreas, and brain. The multiple antidiabetogenic actions of GLP-1 include stimulation of the proliferation and differentiation of the insulin-producing beta cells in the pancreas. The GLP-1 receptor is widely distributed and has been identified in the endocrine pancreas, intestinal tract, brain, lung, kidney, and heart. Here we report the expression of the GLP-1 receptor and proglucagon in the skin of newborn mice located predominantly in the hair follicles, as well as in cultures of skin-derived cells that also express nestin, a marker of cultured cells that have dedifferentiated by epithelial to mesenchymal transition. In cultured skin cells, GLP-1 activates the MAPK/ERK signal transduction pathway, associated with cellular proliferation, differentiation, and cytoprotection. No evidence was found for the activation of cAMP or Ca2+ signaling pathways. Further, redifferentiation of cultured skin-derived cells by incubation in differentiation medium containing GLP-1 induced expression of the proinsulin-derived peptide, C-peptide. These findings suggest a possible paracrine/autocrine role for GLP-1 and its receptor in skin development and possibly also in folliculogenesis.
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PMID:Glucagon-like peptide-1 receptor and proglucagon expression in mouse skin. 1663 Dec 62

Brain size is precisely regulated during development and involves coordination of neural progenitor cell proliferation, differentiation, and survival. The adapter protein ShcA transmits signals from receptor tyrosine kinases via MAPK (mitogen-activated protein kinase)/ERK (extracellular signal-regulated kinase) and PI3K (phosphatidylinositol 3-kinase)/Akt signaling pathways. In the CNS, ShcA expression is high during embryonic development but diminishes as cells differentiate and switches to ShcB/Sck/Sli and ShcC/N-Shc/Rai. To directly test ShcA function in brain development, we used Cre/lox technology to express a dominant-negative form of ShcA (ShcFFF) in nestin-expressing neural progenitors. ShcFFF-expressing mice display microencephaly with brain weights reduced to 50% of littermate controls throughout postnatal and adult life. The cerebrum appeared most severely affected, but the gross architecture of the brain is normal. Body weight was mildly affected with a delay in reaching mature weight. At a mechanistic level, the ShcFFF microencephaly phenotype appears to be primarily attributable to elevated apoptosis levels throughout the brain from embryonic day 10.5 (E10.5) to E12, which declined by E14.5. Apoptosis remained at normal basal levels throughout postnatal development. Proliferation indices were not significantly altered in the embryonic neuroepithelium or within the postnatal subventricular zone. In another approach with the same nestin-Cre transgene, conditional deletion of ShcA in mice with a homozygous floxed shc1 locus also showed a similar microencephaly phenotype. Together, these data suggest a critical role for ShcA in neural progenitor survival signaling and in regulating brain size.
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PMID:Neural-specific inactivation of ShcA results in increased embryonic neural progenitor apoptosis and microencephaly. 1687 Jul 34

In the adult nervous system, neuronal subpopulations sustain a hierarchical pattern of selective vulnerability to hypoxia. Hypoxia also activates quiescent neural progenitor cells (NPCs) resulting in their amplification and subsequent differentiation into neurons and glia. Use of rat organotypic hippocampal cultures facilitates examination of early signaling events in response to hypoxia and reoxygenation that result in neurogenesis. Cultures were exposed to hypoxia for up to 6 h followed by reoxygenation. CA1 neurons showed focal nuclear condensation by 2 h of hypoxia, but CA2 and CA3 neurons were spared. JNKs and c-Jun reached peak activation by 4 h, returning to basal levels by 6 h. Expression of oxygen sensors, hemoxygenase 2 and HIF1, were elevated by 30 min and 2 h, respectively. By 24 h of reoxygenation, there was proliferation of nestin-positive NPCs. With U0126, an upstream inhibitor of ERK activation, BrdU labeling was markedly reduced immunohistochemically as well as PCNA protein expression, suggesting a role for ERKs in the proliferation response. Immunohistochemically, antinestin detected NPCs and on Western blots reached peak levels by 24-48 h of reoxygenation. Proliferation and differentiation of endogenous NPCs in the area of neuronal loss further suggests that mechanisms potentially exist in vitro for replacement with functional neurons.
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PMID:Mitogen-activated protein kinase signaling, oxygen sensors and hypoxic induction of neurogenesis. 1690 37

We propose a new methodology to enhance the vascular differentiation of human embryonic stem cells (hESCs) by encapsulation in a bioactive hydrogel. hESCs were encapsulated in a dextran-based hydrogel with or without immobilized regulatory factors: a tethered RGD peptide and microencapsulated VEGF(165). The fraction of cells expressing vascular endothelial growth factor (VEGF) receptor KDR/Flk-1, a vascular marker, increased up to 20-fold, as compared to spontaneously differentiated embryoid bodies (EBs). The percentage of encapsulated cells in hydrogels with regulatory factors expressing ectodermal markers including nestin or endodermal markers including alpha-fetoprotein decreased 2- or 3-fold, respectively, as compared to EBs. When the cells were removed from these networks and cultured in media conditions conducive for further vascular differentiation, the number of vascular cells was higher than the number obtained through EBs, using the same media conditions. Functionalized dextran-based hydrogels could thus enable derivation of vascular cells in large quantities, particularly endothelial cells, for potential application in tissue engineering and regenerative medicine.
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PMID:Bioactive hydrogel scaffolds for controllable vascular differentiation of human embryonic stem cells. 1734 88


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