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At least 1,027 records · Page 57Linked to original sources
PubMed1983

Changes in malignant phenotype of a human carcinoma conditioned by growth environment.

The human epidermoid carcinoma HEp3 exhibits highly malignant growth in chicken embryos that disappears progressively in cell culture. When studied by clonal analysis, loss of tumorigenicity was apparent within 20 generations and essentially complete after 40 generations in culture; affected all clones; and occurred under conditions which excluded the selection of variants based on superior growth rate in culture. Once ostensibly lost, the malignant phenotype reappeared after prolonged exposure of nontumorigenic cells to in vivo conditions. This similarly affected all clones assayed over a wide range of inoculum sizes. There was no evidence that HEp3 populations were heterogeneous with respect to tumorigenicity, or that the results were due to preferential selection of genetically determined subpopulations. It is suggested that the malignant phenotype of HEp3 is expressed in response to conditions in the physiological environment.

Air↗
PubMed1987

Cell diversification within the myogenic lineage: in vitro generation of two types of myoblasts from a single myogenic progenitor cell.

We show that a single myogenic progenitor cell in vitro generates two types of myoblasts committed to two distinct myogenic cell lineages. Using fast and slow myosin heavy chain isoform content to define myotube type, we found that myogenic cells from fetal quail (day 10 in ovo) formed two types of myotubes in vitro: fast and mixed fast/slow. Clonal analysis showed that these two types of myotubes were formed from two types of myoblasts committed to distinct fast and fast/slow lineages. Serial subcloning demonstrated that the initial myoblast progeny of an individual myogenic progenitor cell were in the fast lineage, whereas later progeny were in the fast/slow lineage. Fast and slow myosin expression within particular myotubes reflects the genetic processes underlying myoblast commitment to diverse myogenic lineages.

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PubMed1989

The ski oncogene induces muscle differentiation in quail embryo cells.

Quail embryo cells (QECs) are primary cultures of fibroblastoid cells that become myogenic after infection with avian retroviruses expressing the ski oncogene (SKVs). ski also stimulates proliferation of QECs and induces morphological transformation and anchorage-independent growth. Paradoxically, ski-transformed clones picked from soft agar are capable of muscle differentiation. ski-induced differentiation is essentially indistinguishable from that of uninfected myoblasts in culture with regard to muscle-specific gene expression, commitment, and inhibition by growth factors or other oncogenes. However, ski-induced myoblasts have less stringent requirements for growth and differentiation. Uninfected QECs cannot differentiate and do not express an early marker for the myogenic lineage. Clonal analysis indicates that at least 40% of QECs are converted by ski to differentiating myoblasts. The data suggest that ski induces either the capacity for differentiation in an "incompetent" muscle precursor or the determination of nonmyogenic cells to the myogenic lineage.

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PubMed1994

Glial growth factor restricts mammalian neural crest stem cells to a glial fate.

Growth factors and cytokines are thought to influence the development of uncommitted progenitor cell populations, but the issue of how these factors act on individual cells remains controversial. Such factors may act simply as selective mitogens or survival factors for cells that undergo lineage restrictions stochastically. Alternatively, they may instruct or bias multipotent cells to choose one lineage at the expense of others. Here we show that glial growth factor (GGF), previously defined as a Schwann cell mitogen, strongly suppresses neuronal differentiation of rat neural crest stem cells while promoting or allowing glial differentiation. Quantitative clonal analysis suggests that the action of GGF is likely to be instructive rather than selective. Taken together with the expression pattern of GGF, these data suggest a lateral signaling model for the diversification of cell types within developing peripheral ganglia.

Animals↗
PubMed1986

Inducibility of terminal differentiation in daunomycin- and cytosine arabinoside-resistant mouse myeloid leukemia M1 cells.

Studies were made on whether differentiation and proliferation of antitumor drug-resistant leukemia cells could be controlled by specific inducers of terminal differentiation. Leukemia subclones resistant to daunomycin and/or cytosine arabinoside were isolated from differentiation-inducible mouse myeloid leukemia M1-B24 cells by selection with these antitumor drugs. The drug-resistant cells were found to retain their potential for terminal differentiation induced by various inducers, such as a protein inducer in the conditioned medium of mouse L929 cells, dexamethasone, 1 alpha,25-dihydroxyvitamin D3, 2-[2-(dodecyloxy)ethoxy]ethyl 2-pyridinioethyl phosphate, and poly I. Differentiated cells showed morphological changes to mature macrophage-like cells, increase in phagocytic activity, and decrease in proliferative activity. Clonal analysis of M1-B24 cells showed that the cellular responses to the protein inducer of differentiation were not significantly different between drug-resistant clones selected with anti-tumor drugs and control (drug-sensitive) clones randomly isolated without selection. These results suggest that induction of differentiation of leukemic cells with the specific inducers is another approach to control the drug-resistant leukemia.

Animals↗
PubMed1994

Regulation of the early development of the nervous system by growth factors.

Development of the nervous system, although patterned by intrinsic genetic expression, appears to be dependent on growth factors for many of the differentiation steps that generate the wide variety of neurons and glia found in the both the central and peripheral nervous system. By using in vitro assays, including clonal analysis, the precise function of the various growth factors and the differentiation potential of the various neural populations has begun to be described. This review discusses some of the recent findings and examines how neuronal differentiation may result from the interaction of several growth factors.

Animals↗
PubMed1993

Immunoreactive fucosylceramide as a B-cell differentiation marker.

The reactivity of PC47H, a monoclonal antibody (mAb) directed against fucosylceramide, with cells of lymphoid lineage was examined. Immunoreactive fucosylceramide (FC) was recognized only in pokeweed mitogen (PWM)-stimulated B blasts, plasma cells and germinal center cells. mAb PC47H did not react with T cells at different stages or with peripheral blood B cells. Furthermore, FC was expressed abundantly in blastic cells of B-cell lymphoma, multiple lymphoma and myeloma cell lines KMS-12-BM and KMS-12-PE. In other words, FC was expressed more strongly in mature than in immature B cells. Immunoelectron microscopy showed that FC was located in the plasma membrane and rough endoplasmic reticulum. mAb PC47H can therefore be used as a unique B-cell differentiation marker for study of B-cell activation and differentiation and clonal analysis of lymphoid malignancies.

Animals↗
PubMed1982

Immunogenic variants obtained by mutagenesis of mouse Lewis lung carcinoma. Recognition of variant-specific antigens by cytolytic T lymphocytes.

By mutagenesis of a cell line derived from Lewis lung carcinoma (3LL), it is possible to obtain at high frequency stable tumor cell variants (tum-) that are rejected by syngeneic mice. The possibility of obtaining a cytolytic T cell (CTL) response directed specifically against these tum- variants was examined. With the four variants that were analysed, a significant cytolytic activity was obtained with peritoneal cells from immune mice collected shortly after an intraperitoneal boost and also with spleen cells after a secondary stimulation in vitro. The CTL populations preferentially lysed the immunizing tum- variant, while also showing a cross-reactive lysis against the other variants and the original 3LL cells. Highly active CTL clones could be isolated from limiting dilution microcultures of these CTL populations. The clonal analysis clearly showed the existence of two distinct CTL populations, one directed exclusively against the immunizing variant and another that lysed all 3LL targets equally. This CTL specificity analysis therefore demonstrates directly the presence of new antigens on the 3LL tum- cell variants.

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PubMed1991

Role of the neurotrophic factors BDNF and NGF in the commitment of pluripotent neural crest cells.

Since trophic factors are increasingly recognized as playing a role in some decision-making steps during development, the influence of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) on the commitment of pluripotent neural crest cells was investigated by in vitro clonal analysis. BDNF caused an increase of up to 21-fold in the number of sensory neuron precursors per colony without a corresponding increase in the total number of cells. By contrast, BDNF treatment caused an equivalent decrease in the number of undifferentiated cells per colony. The data suggest that BDNF, but not NGF, directs pluripotent neural crest cells to differentiate along the primary sensory neuron lineage.

Animals↗
PubMed1994

Cell proliferation patterns in the wing imaginal disc of Drosophila.

Morphogenetic processes, based on the temporal and spatial control of cell proliferation, are involved in determining the size and shape of an organism. We have used clonal analysis, employing X-ray-induced mitotic recombination, to study cell proliferation and differentiation processes in the developing wing imaginal disc of Drosophila. Our results show a non-uniform distribution of mitotic activities during different stages of wing development. This may reflect waves of cell proliferation which derive from distinct centers of cell proliferation within the growing wing imaginal disc. These proliferation centers are located within the major wing compartments (i.e. the anterior, posterior, dorsal and ventral compartments) and they are restricted to the areas which give rise to the intervein regions of the adult wing. The mitotic recombination analysis, combined with the study of Minute and gynandromorph mosaics, show that the presumptive vein regions of the wing represent distinct boundaries which delimit the proliferation centers to the intervein regions. We present a generative model of wing morphogenesis that is consistent with our results.

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PubMed1992

High frequency of tumour cell reversion to non-tumorigenic phenotype.

Nine spontaneously transformed cell lines were isolated from embryo fibroblasts of mice and rats with different genotypes. In six cell lines highly tumorigenic cell variants were selected. At the start of culture all cell lines were of low or zero tumorigenicity. The same cells in a confluent monolayer in vitro had high contact inhibition of growth and proliferated in response to stimulation by growth factors. Tumour progression of the established lines was accompanied by significant changes of these properties. Clonal analysis of the six most malignant cell lines revealed their capacity to revert simultaneously to the non-tumorigenic state and to their initial growth characteristics. Frequencies of reversion to the non-tumorigenic phenotype were much higher than re-reversion to the tumorigenic phenotype. The reversions occurred in several sequential passages of transformed clones, with some variations in individual clones. These observations suppose that frequencies of tumour reversions are a constant genetic characteristic of every cell line.

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PubMedDate not supplied

Plasticity of human satellite cells.

Satellite cells were isolated from human quadriceps and masseter muscles and the phenotype of these cells examined in vitro. The expression of the different isoforms of the myosin heavy chains (embryonic, fetal, fast and slow) and light chain isoforms was used to assay myotube diversification. We found that fused cultures of human satellite cells express adult fast and slow MHCs in addition to the embryonic and fetal isoforms. Only the four fast light chains (MLC1emb, MLC1F, MLC2F and MLC3F) were synthesized. No slow MLCs were ever detected in these cultures. In order to determine if the human satellite cells were committed to distinct fast and slow myogenic lineages, a clonal analysis was carried out on both cell populations. All myogenic clones expressed fast and slow MHCs, suggesting that there is no evidence for different fast and slow satellite cell lineages in human skeletal muscle.

Biopsy↗
PubMed2006

Adult pancreatic stem/progenitor cells spontaneously differentiate in vitro into multiple cell lineages and form teratoma-like structures.

Cells isolated from pancreas have a remarkable potential for self-renewal and multilineage differentiation. We here present a comprehensive characterisation of stem/progenitor cells derived from exocrine parts of the adult rat pancreas. Using purified cells from either single colonies or even single-cell clones, we specifically demonstrate: (i) the cells contain the typical stem/progenitor cell markers alkaline phophatase, SSEA-1, Oct-4, CD9, Nestin, Pax6, CD44, a-Fetoprotein and Brachyury, demonstrated by immunocytochemistry and RT-PCR; (ii) the cells have the potential to differentiate into lineages of all three germ layers in vitro; (iii) a clonal analysis revealed that even cell lines derived from a single cell have stem/progenitor cell properties such as self-renewal and spontaneous differentiation into various cell lineages; (iv) the cells have the propensity to form three-dimensional, teratoma-like structures in vitro, which contain cells of different lineages; and (v) external stimuli can activate the generation of certain cell types. For instance, cells treated with retinoic acid show an increased expression of alpha-smooth muscle actin. These results suggest that exocrine glands, such as pancreas may be a potential source of adult stem/progenitor cells, suitable for cell therapy of degenerative diseases.

Actins↗
PubMed2004

Mesothelial progenitor cells and their potential in tissue engineering.

The mesothelium consists of a single layer of flattened mesothelial cells that lines serosal cavities and the majority of internal organs, playing important roles in maintaining normal serosal integrity and function. A mesothelial 'stem' cell has not been identified, but evidence from numerous studies suggests that a progenitor mesothelial cell exists. Although mesothelial cells are of a mesodermal origin, they express characteristics of both epithelial and mesenchymal phenotypes. In addition, following injury, new mesothelium regenerates via centripetal ingrowth of cells from the wound edge and from a free-floating population of cells present in the serosal fluid, the origin of which is currently unknown. Recent findings have shown that mesothelial cells can undergo an epithelial to mesenchymal transition, and transform into myofibroblasts and possibly smooth muscle cells, suggesting plasticity in nature. Further evidence for a mesothelial progenitor comes from tissue engineering applications where mesothelial cells seeded onto tubular constructs have been used to generate vascular replacements and grafts to bridge transected nerve fibres. These findings suggest that mesothelial cell progenitors are able to switch between different cell phenotypes depending on the local environment. However, only by performing detailed investigations involving selective cell isolation, clonal analysis together with cell labelling and tracking studies, will we begin to determine the true existence of a mesothelial stem cell.

Animals↗
PubMed2006

Secretion of Wnt ligands requires Evi, a conserved transmembrane protein.

Wnt signaling pathways are important for multiple biological processes during development and disease. Wnt proteins are secreted factors that activate target-gene expression in both a short- and long-range manner. Currently, little is known about how Wnts are released from cells and which factors facilitate their secretion. Here, we identify a conserved multipass transmembrane protein, Evenness interrupted (Evi/Wls), through an RNAi survey for transmembrane proteins involved in Drosophila Wingless (Wg) signaling. During development, evi mutants have patterning defects that phenocopy wg loss-of-function alleles and fail to express Wg target genes. evi's function is evolutionarily conserved as depletion of its human homolog disrupts Wnt signaling in human cells. Epistasis experiments and clonal analysis place evi in the Wg-producing cell. Our results show that Wg is retained by evi mutant cells and suggest that evi is the founding member of a gene family specifically required for Wg/Wnt secretion.

Animals↗
PubMed2006

Stem cells signal to the niche through the Notch pathway in the Drosophila ovary.

Stem cells are maintained and retain their capacity to continue dividing because of the influence of a niche. Although niches are important to maintain "stemness" in a wide variety of tissues, control of these niches is poorly understood. The Drosophila germline stem cells (GSCs) reside in a somatic cell niche. We show that Notch activation can induce the expression of niche-cell markers even in an adult fly; overexpression of Delta in the germline, or activated Notch in the somatic cells, results in extra niche cells, up to 10-fold over the normal number. In turn, these ectopic niche cells induce ectopic GSCs. Conversely, when GCSs do not produce functional Notch ligands, Delta and Serrate, the TGF-beta pathway is not activated in the GSCs, and they differentiate and subsequently leave the niche. Importantly, clonal analysis reveals that the receiving end of the Notch pathway is required in the somatic cells. These data show that a feedback loop exists between the stem cells and niche cells. Demonstration that stem cells can contribute to niche function has far-reaching consequences for stem cell therapies and may provide insight into how cancer can spread throughout an organism via populations of cancer stem cells.

Animals↗
PubMed2004

Properties of cortical precursor cells cultured long term are similar to those of precursors at later developmental stages.

In vitro cultures of neural precursor cells are useful experimental tools for studies on the mechanisms of brain development, as well as for generating renewable sources in cell therapy for neurodegenerative disorders. The systematic characterization of cultured neural precursors is a prerequisite for obtaining basic information on brain development. Here, we examine the cell survival, proliferation, and differentiation potential of cultured neural precursors from different embryonic ages and those of the precursors expanded in vitro for different periods of time. Precursor cells were isolated at rat embryonic days 14 (E14) and 19 (E19) and cultured in the presence of a mitogen basic fibroblast growth factor (bFGF). The numbers of TUNEL+ and BrdU+ cells in E19 cortical precursor cultures were significantly lower than those in E14 cultures, indicating that the programmed cell death and proliferation potential of neural precursors are reduced during the progression of brain development. E14 cells tended to differentiate into neurons, and E19 cells into astrocytes. To determine whether the intrinsic properties of neural precursors are similarly altered during in vitro culture, E14 precursor cells were expanded for different periods. Precursor cells expanded for longer periods displayed lower apoptotic and proliferation indices, as well as astrogenic developmental potential. Clonal analysis data confirmed the transition of precursor differentiation potential from neurogenic to astrogenic over the culture period. Our findings collectively suggest that neural precursor cells undergo time-dependent changes in properties via an intrinsic program, both in vivo and in vitro.

Animals↗
PubMed2004

BMP signaling initiates a neural crest differentiation program in embryonic rat CNS stem cells.

Bone morphogenetic proteins (BMPs) have an important role in neuronal and astrocytic differentiation of embryonic and adult neural stem cells (NSCs). Here, we show that BMP6, BMP7, GDF5, and GDF6 instructively differentiate E12, E14, and E17 rat cortical NSCs into a variety of neural crest lineages. Clonal analysis shows that BMP7-treated NSCs develop mostly into smooth muscle and peripheral glia. We observed a rapid induction of premigratory neural crest markers like p75NTR, and AP-2 alpha followed by Msx1, Msx2, and Slug, transcription factors that participate in neural crest development. These results suggest that NSCs cultured in vitro in the presence of FGF2 display expanded developmental potential.

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