Showing papers on "Cellular differentiation published in 1977"
TL;DR: These cell lineages range in length from one to eight sequential divisions and lead to significant developmental changes in the neuronal, muscular, hypodermal, and digestive systems and are determined by direct observation of the divisions, migrations, and deaths of individual cells in living nematodes.
3,407 citations
TL;DR: The derivation from myeloid leukaemic cells of a leukocyte culture is described here for the first time that by morphological and histochemical criteria clearly and persistently differentiates along the myeloids series without an exogenous source of conditioned medium.
Abstract: ATTEMPTS to develop long-term suspension cultures of human myeloid leukaemic cells have met with limited success. Lymphoblastoid lines carrying the Epstein–Barr virus genome occasionally arise during such attempts but these lymphoid cells originate from contaminating B lymphocytes and not from the leukaemic myeloid cells1. A line established from the pleural fluid of a patient with chronic myeloid leukaemia in blast crisis2 (designated K-562) has no B-cell or T-cell markers3–4 and does not seem to be of lymphoid origin4. Its lack of morphological and histochemical differentiation2–4, however, makes it difficult to determine whether these cells are derived from myeloblasts or more primitive stem cells4. Another less documented cell line (8261) derived from the peripheral blood of a patient with acute myelogenous leukaemia showed apparent morphological and functional differentiation in agar in the presence of a feeder layer of peripheral blood leukocytes but did not differentiate in suspension culture5. Our laboratory previously reported that cultures of differentiating myeloid leukaemic cells can be maintained for several months in suspension culture but only when enriched with conditioned media (CM) from certain monolayer fibroblastic cultures of first trimester whole human embryos (ref. 6 and Ruscetti et al. in preparation). We describe here for the first time the derivation from myeloid leukaemic cells of a leukocyte culture that by morphological and histochemical criteria clearly and persistently differentiates along the myeloid series without an exogenous source of conditioned medium.
2,115 citations
TL;DR: The present report describes the isolation of a cloned population of myogenic cells, derived from adult dystrophic mouse muscle, that can proliferate and differentiate in cell culture.
Abstract: THE muscular dystrophies are a group of hereditary disorders manifested by a progressive wasting of the skeletal muscles. In spite of extensive studies, the nature of the primary lesion is unknown (for review see ref. 1). Because of the complex interaction between tissues, it is difficult to study this question in vivo. Therefore attempts have been made to investigate this question in cultures of dystrophic muscles of human or animal origin. Tissue explants as well as monolayer primary cell cultures contain, in addition to the myogenic cells, a heterogeneous cell population, the composition of which might differ in normal and dystrophic muscle cultures. It is difficult in such experiments to distinguish between properties intrinsic to the myogenic cells and effects exerted by other cell types. Indeed, previous experiments have yielded conflicting conclusions2–6. We therefore tested the possibility of obtaining cell cultures consisting of pure populations of myogenic cells obtained from dystrophic muscles. The present report describes the isolation of a cloned population of such cells, derived from adult dystrophic mouse muscle, that can proliferate and differentiate in cell culture.
2,039 citations
TL;DR: Dissociated normal mammary epithelial cells from prelactating mice were plated on different substrates in various medium-serum-hormone combinations to find conditions that would permit maintenance of morphological differentiation.
Abstract: Dissociated normal mammary epithelial cells from prelactating mice were plated on different substrates in various medium-serum-hormone combinations to find conditions that would permit maintenance of morphological differentiation. Cells cultured on floating collagen membranes in medium containing insulin, hydrocortisone and prolactin maintain differentiation through 1 month in culture. The surface cells form a continuous epithelial pavement. Some epithelial cells below the surface layer rearrange themselves to form alveolus-like structures. Cells at both sites display surface polarization; microvilli and tight junctions are present at their medium-facing or luminal surface and a basal lamina separates the epithelial components from the gel and stromal cells. Occasinal myoepithelial cells, characterized by myofilaments and plasmalemmal vesicles, are identified at the basal surface of the secretory epithelium. In contrast, cells cultured on plastic, glass or collagen gels attached to Petri dishes form a confluent epithelial sheet showing surface polarization, but lose secretory and myoepithelial specializations. If these dedifferentiated cells are subsequently maintained on floating collagen membranes, they redifferentiate. There is little DNA synthesis in cells on collagen gels, in contrast to Petri-dish controls. Protein synthesis in cells on floating collagen membranes increases over T0 values and remains constant through 7 days in culture whereas it decreases on attached gels; however, if the gels are freed to float, protein synthesis increases sharply and parallels that seen on floating membranes.
608 citations
TL;DR: Three aspects of terminal differentiation of the epidermal keratinocyte have been studied in cell culture—the development of detergent-insoluble cytoplasmic filaments, the formation of a cornified cell envelope and the destruction of the cell nucleus.
515 citations
TL;DR: This chapter discusses the cell polyploidy and its relation to tissue growth and function and the mechanism of supplanting mitotic syntheses by tissue-specific ones as the cause of reduction in the stages of mitosis may be common for different cell populations.
Abstract: Publisher Summary This chapter discusses the cell polyploidy and its relation to tissue growth and function. Cytophotometry established a fundamental similarity between polyploidy and polyteny, their common feature being multiple doubling of DNA in the cell. The occurrence and properties of polyploid cell populations is discussed. Polyploid nuclei have been found in protozoa and in the cells of many metazoa, both animals and plants. The common property of polyploid cell populations is retention of ability to reproduce DNA by differentiating and often fully differentiated cells. The stem cell phenomenon, which is clearly defined in many diploid cell populations, is in polyploid ones deprived of its main function being the only source of proliferation. The mode of polyploidy is briefly explained. Different types of mitotic polyploidization proper, complete abolition of the mitotic mechanism, and other cases of increases in the DNA content of cells are considered. The mechanism of supplanting mitotic syntheses by tissue-specific ones as the cause of reduction in the stages of mitosis may be common for different cell populations. But polyploidy in different tissues may have a different meaning associated with the specific function of the tissue. Polyploidization, as a rule, accompanies cell differentiation.
382 citations
TL;DR: A method is presented for growing large numbers of pure isolated smooth muscle cells from adult human, monkey, and rabbit blood vessels in primary culture to modify or “dedifferentiated” after about 9 days in culture to morphologically resemble fibroblasts.
Abstract: A method is presented for growing large numbers of pure isolated smooth muscle cells from adult human, monkey, and rabbit blood vessels in primary culture. In the first few days in culture these cells closely resembled those in vivo and could be induced to contract with angiotensin II, noradrenaline and mechanical stimulation. They stained intensely with antibodies against smooth muscle actin and myosin. Fibroblasts and endothelial cells did not stain with these antibodies thereby allowing the purity of each batch of cultures to be monitored. This was consistently found to be better than 99%. The smooth muscle cells modified or "dedifferentiated" after about 9 days in culture to morphologically resemble fibroblasts. At this stage cells could no longer be induced to contract and did not stain with the myosin antibodies. Intense proliferation of these cells soon resulted in a confluent monolayer being formed at which stage some differentiated characteristics returned. The modification of "dedifferentiation" process could be inhibited by the presence of a feeder layer of fibroblasts or endothelial cells, or the addition of cAMP to the culture medium. Smooth muscle cells which had migrated from explants in primary culture, and cells in subculture, had morphological and functional properties of "dedifferentiated" cells at all times. The advantages of differentiated rather than "dedifferentiated" smooth muscle cells in culture for the study of mitogenic agents in atherosclerosis is discussed.
374 citations
TL;DR: Experiments are described showing that the multinucleated tubular cells which arise in C3H 10T½ C18 cells treated with aza-CR are in fact functional myotubes.
Abstract: 5-AZACYTIDINE (aza-CR)—a s-triazine nucleoside analogue of cytidine—has strong inhibitory effects in various biological systems including neoplasms: it is a powerful bacteriostatic, antitumour and mutagenic agent1. Aza-CR also exhibits immunosuppressive, antimitotic, radioprotective and virostatic effects1. The cytostatic effect of aza-CR has primarily been directed against leukaemia2 and it has been used to treat human solid tumours3. During a study on the morphological transformation of C3H 10T½ C18 cells by cancer chemotherapeutic agents, it was noted that elongated multinucleated cells arose in cultures exposed to aza-CR4. The C3H 10T½ C18 line is a clonal line of mouse embryo cells developed at the McArdle Laboratory for Cancer Research for use in studies on chemical oncogenesis in vitro5–10. The cells are highly sensitive to post-confluence inhibition of cell division, show a remarkably low rate of spontaneous transformation and grow with a fibroblast-like morphology with long cytoplasmic processes in sparse cultures. When confluent, they form flat even monolayers and appear epithelioid. Scanning electron microscopy has shown the confluent cells to be extremely thin and polygonal with smooth surfaces resembling epithelial cells11. Here we describe experiments showing that the multinucleated tubular cells which arise in C3H 10T½ C18 cells treated with aza-CR are in fact functional myotubes.
333 citations
TL;DR: It is found that tissue mast cells can be derived from grafted bone marrow cells in irradiated mice, using the giant granules of beige mouse5 as a quantitative marker for mast cells.
Abstract: BOTH basophilic granulocytes and tissue mast cells are known to have receptors for immunoglobulin E (IgE) and granules which contain histamine and heparin1,2. In spite of their similar physiological role, these two types of cells are thought to be independent cell lineages; the former are derived from the bone marrow, and the latter are connective tissue cells2. The differentiation of mast cells from their precursors, which were supposed to be undifferentiated mesenchymal cells, and the proliferation of these precursors were reported to occur in the skin of mice3,4. These results do not necessarily exclude the possibility that the precursor cells themselves are originated from the bone marrow, however. To examine such a possibility, we investigated whether mast cells of the donor origin appeared in radiation chimaeras, using the giant granules of beige (Chediak–Higashi syndrome) mouse5 as a quantitative marker for mast cells. We have found that tissue mast cells can be derived from grafted bone marrow cells in irradiated mice.
303 citations
TL;DR: Dfferentiation properties of a cell line, L84, which originated from a non-fusing clone isolated from the myogenic line L8, are described and show that L84 cells retain the programme for their differentiation into muscle fibres.
296 citations
TL;DR: It is reported here that PMA mimics some of the effects of the Rous sarcoma tumour agent on myogenesis, and of the purified phorbol esters, PMA is the most potent as a tumour-promoting agent and as a mitogen.
Abstract: EVIDENCE that viruses and chemical carcinogens alter the ongoing synthetic programme of cells has been presented1,2 Chondroblasts and melanoblasts transformed with a temperature-sensitive Rous sarcoma virus cease synthesising the chondroblast-unique sulphated proteoglycan and melanin, respectively3 Shifted to non-permissive temperature, these cells re-initiate the synthesis of the chondroblast-unique sulphated proteoglycan and melanin Similar results have been obtained using chick myogenic cells4,5 Normal presumptive myoblasts undergo a limited number of replications, yielding postmitotic, mononucleated myoblasts Postmitotic myoblasts initiate the synthesis of muscle-specific myosin heavy and light chains and fuse into myotubes6,7 In contrast, ts-viral transformed myogenic cells continue to replicate, do not initiate the synthesis of muscle-specific myosins and do not fuse 24–48 h after shifting to non-permissive temperature, many transformed myogenic cells withdraw irreversibly from the cell cycle, initiate the synthesis of muscle-specific (unpublished data) myosins and fuse Apparently when the transformation factor is expressed the cells do not withdraw from the cell cycle, and as a consequence of being forced to cycle, do not terminally differentiate To probe the mechanisms that might be common to the generation of terminally differentiated cells from normal precursor cells, and to the generation of malignant cells from normal precursor cells, we studied the effects of phorbol-12-myristate-13-acetate (PMA) on myogenesis Of the purified phorbol esters, PMA is the most potent as a tumour-promoting agent and as a mitogen8–12 We report here that PMA mimics some of the effects of the Rous sarcoma tumour agent on myogenesis
TL;DR: The case for the lymphocyte population of the mouse is presented as material for studying the molecular biology of cellular differentiation from the viewpoint that mechanisms established for the various cell populations termed 'lymphocytes' may be relevant to differentiation generally.
Abstract: We shall present the case for the lymphocyte population of the mouse as material for studying the molecular biology of cellular differentiation. This will be discussed from the viewpoint that mechanisms established for the various cell populations cx)llectively termed 'lymphocytes' may be relevant to differentiation generally. The importance of selecting suitable systems for investigating cellular differentiation is obvious. Each of the better known models has its attraction. The slime mold, Dictyostelium discoideum, offers the advantages of a primitive organism in which the essentials of cellular differentiation are represented without the elaborations of more highly evolved forms. The T/t locus of the mouse is prominent as a model of embryogenetic differentiation, in an organism phylogenetically close to man himself. We describe here several unique opportimities afforded by the mouse lympho^ cyte model.
TL;DR: The pattern of development in the embryoid bodies is remarkably similar to that in normal mouse embryogenesis up to the time of formation of the third germ layer, the mesoderm, which in most cases arises by a process which has not previously been described.
TL;DR: Another cell system, mouse preadipose cells, is described, in which tumour promoters inhibit terminal differentiation, and it is confirmed that there is a good correlation between the ability of a particular phorbol diester to promote tumours in mouse skin and its ability to inhibit terminals differentiation of cells in culture.
Abstract: TUMOUR-PROMOTING compounds are not themselves carcinogenic, but can induce skin tumours in mice pretreated with a subcarcinogenic dose of a chemical carcinogen1–3. They have been shown to produce many different biochemical and biological effects on cells3,4, but the mechanism of promotion is not known. Two recent reports describe the effects of the phorbol diester series of tumour promoters on cell differentiation in vitro. Cohen et al.5 observed that 12-O-tetradecanoyl-phorbol-13-acetate (TPA; phorbol myristate acetate), a potent promoter, inhibits myogenesis in chick embryo muscle cultures. We have reported6,7 that TPA and other tumour-promoting phorbol diesters inhibit spontaneous and induced differentiation of Friend erythroleukaemia cells in culture. We now describe another cell system, mouse preadipose cells, in which tumour promoters inhibit terminal differentiation, and confirm in these cells our original observation6 that there is a good correlation between the ability of a particular phorbol diester to promote tumours in mouse skin and its ability to inhibit terminal differentiation of cells in culture.
TL;DR: The findings suggest that the capability for expression of Hb F in terminally differentiated cells of the adult is determined at the level of less-differentiated erythroid stem cells with characteristics of burst-forming units.
Abstract: The in vitro regulation of fetal hemoglobin (HbF was investigated in clones of cultured adult human erythroid cells by in situ immunofluorescent identification of the hemoglobins synthesized. Formation of Hb F-containing clones was enhanced by erythropoietin and by culture conditions favoring the proliferation of less-differentiated stem cells of the burst-forming-unit type. Burst-forming units differed in their capacity to direct Hb F synthesis in their terminally differentiated progeny. A class of early precursors that can produce descendent stem cells with or without commitment to Hb F production was identified. The findings suggest that the capability for expression of Hb F in terminally differentiated cells of the adult is determined at the level of less-differentiated erythroid stem cells with characteristics of burst-forming units. It is proposed that the regulation of Hb F synthesis in vivo is also linked to the process of differentiation of the erythroid stem cells and that the patterns of Hb F synthesis during ontogeny reflect the attainment of progressively higher levels of differentiation of erythroid stem cells as development proceeds.
TL;DR: Clones of Friend erythroleukemia cells, characterized by the presence of 40-70% benzidine-positive cells synthesizing hemoglobin in the absence of inducing drugs, were treated with several phorbol diesters with a known range of tumor-promoting activity on mouse skin and retained a high potential for spontaneous differentiation.
Abstract: Clones of Friend erythroleukemia cells, characterized by the presence of 40-70% benzidine-positive cells synthesizing hemoglobin in the absence of inducing drugs, were treated with several phorbol diesters with a known range of tumor-promoting activity on mouse skin. Good correlation was found between the reported tumor-promoting activity of a particular phorbol diester and its ability to inhibit spontaneous erythroid differentiation in culture. The inhibition of differentiation by 12-O-tetradecanoyl-phorbol-13-acetate, the most active tumor promoter, was maximum after 4 days of treatment; this inhibition was reversed by removal of the phorbol diester no matter how long the period of treatment. Unlike control cells, which gradually revert to a population with a low percentage of benzidine-positive cells, cells treated with 12-O-tetradecanoyl-phorbol-13-acetate retained a high potential for spontaneous differentiation.
TL;DR: The degree of hypomethylation of DNA and tRNA from FL cells induced to differentiate with dimethylsulfoxide and butyrate, and DNA isolated from cells exposed to any of the three inducers, suggest that methylation ofDNA may play a role in the regulation of gene expression.
Abstract: This report identifies l-ethionine as an inducer of differentiation in murine erythroleukemia cells. When Friend erythroleukemia cells are grown in the presence of 4 mM l-ethionine, globin mRNA accumulates and in 4–5 days, 25–30% of the cells in the culture contain hemoglobin. Incubation of the cells with bromodeoxyuridine prevents both ethionine-induced accumulation of globin mRNA and erythroid differentiation.
At the concentration where l-ethionine acts as an inducer of FL cell differentiation it inhibits methylation of DNA and tRNA in vivo but does not prevent macromolecular synthesis or cell division.
To establish whether a link existed between inhibition of a specific methyltransferase and activation of globin synthesis in FL cells, we examined the degree of hypomethylation of DNA and tRNA from FL cells induced to differentiate with dimethylsulfoxide and butyrate.
In contrast to the tRNA from ethionine-treated cells, tRNA from cells induced by butyrate or Me2SO cannot be methylated in vitro using homologous enzymes.
DNA isolated from cells exposed to any of the three inducers, however, was significantly hypomethylated when compared with DNA from uninduced cells. These data suggest that methylation of DNA may play a role in the regulation of gene expression.
TL;DR: It is suggested that control of murine leukemia virus replication in the cells is a function of the stage of differentiation and perhaps also of the genetic composition of the teratocarcinoma stem cells.
TL;DR: The observed localization of nerve and nematocyte differentiation in whole hydra probably occurs at the level of stemcell determination, suggesting that a stem cell's decision to proliferate or differentiate is regulated by shortrange feedback signals which are already saturated in young clones.
TL;DR: The action of testosterone on the differentiation and secretory activity of a target organ and the secretory tubules of the submaxillary gland constitute an original material for studying the controlling action ofosterone since they are different from the classic testosterone effectors.
Abstract: Publisher Summary This chapter discusses the action of testosterone on the differentiation and secretory activity of a target organ. In spite of their functional complexity, the secretory tubules of the submaxillary gland constitute an original material for studying the controlling action of testosterone since they are different from the classic testosterone effectors. Indeed, in the male accessory sexual organs, testosterone induces a cellular differentiation toward secretory activity. In its absence, the glandular epithelium reverts to an undifferentiated state. Such is not the case for the tubular cells of the submaxillary gland which possesses two distinct poles of functional activity: the basal pole where cellular exchanges take place and the apical pole where secretions occur. These two functions are more or less developed, depending on the hormonal environment, so that cell differentiation may be oriented toward one function or the other by manipulation of this environment. When deprived of testosterone by castration in the male mouse, the actively secreting tubular cells do not undergo a simple involution, but reorient their differentiation in the direction of cellular exchanges. When once again exposed to the action of the androgen steroid they rapidly redevelop the structures directly involved in their renewed secretory functions.
TL;DR: Induction by insulin in receptor-specific changes in 125I-labeled insulin binding to 3T3-L1 cells appears to be differentiation-dependent and not a general response of cells to the culture conditions.
Abstract: Expression of the adipocyte phenotype by differentiating 3T3-L1 preadipocytes occurs upon exposure of the cells to insulin. Differentiation-linked changes in 125I-labeled insulin binding to 3T3-L1 cells were monitored and compared with those in nondifferentiating 3T3-C2 controls treated similarly. Without chronic insulin treatment, 3T3-L1 cells failed to express the adipocyte phenotype but maintained a level of 25,000-35,000 insulin-binding sites per cell. Treatment of 3T3-L1 cells with insulin resulted in an initial suppression of insulin binding followed by a 12-fold increase that paralleled the appearance of differentiated cells. A maximum of 170,000 insulin-binding sites per cell was attained for a population in which greater than 75% of the cells had differentiated. The increase of insulin receptor level appears to be differentiation-dependent and is not a general response of cells to the culture conditions. 3T3-C2 cells maintained in the presence of insulin for 30 days exhibited the undifferentiated phenotype and suppressed levels of insulin binding (35,000 sites per cell). The binding capacity of 3T3-L1 cells for epidermal growth factor remained unchanged between 25,000 and 40;000 sites per cell and was independent of the state of differentiation. Thus, induction by insulin in receptor-specific changes. Insulin receptors increase in number but epidermal growth factor receptors remain constant.
TL;DR: A microwell culture system was developed for analysis of cell movements and interactions during nervous system histogenesis, identifying granule cells in several stages of differentiation, basket and/or stellate neurons, some larger neurons, and two types of neuroglial cells in reproducible, nonrandom patterns by scanning and transmission electron microscopy.
Abstract: A microwell culture system was developed for analysis of cell movements and interactions during nervous system histogenesis. Cells from trypsinized 7-day-old mouse cerebellum reaggregated within hours into clusters which later developed interconnections consisting of either sheets of migrating cells and cell processes or cables of fiber bundles with cells migrating along their surfaces. Granule cells in several stages of differentiation, basket and/or stellate neurons, some larger neurons, and two types of neuroglial cells were identified in reproducible, nonrandom patterns by scanning and transmission electron microscopy. Axonal and dendritic processes, both with growth cones, and numerous synapses were generated in vitro.
TL;DR: A culture system is described in which bone marrow-derived adherent cells can support prolonged proliferation and differentiation of genetically incompatible stem cells and precursor cells, suggesting that the reactive cells responsible in vivo for host transplantation resistance and for graft-versus-host disease are selectively lost or inhibited in such cultures.
Abstract: A culture system is described in which bone marrow-derived adherent cells can support prolonged proliferation and differentiation of genetically incompatible stem cells and precursor cells. The results suggest that the reactive cells responsible in vivo for host transplantation resistance and for graft-versus-host disease are selectively lost or inhibited in such cultures, which may provide a vehicle for studying some of the cellular mechanisms involved in transplantation resistance.
TL;DR: Functional analysis of the unreactive (TH1-) and reactive T-cell subclasses demonstrated that TH1- cells mounted a good proliferative response to a battery of specific soluble antigens but neither responded in MLC, nor elaborated LMF in response to tetanus toxoid.
Abstract: A heterologous antihuman T-cell serum (anti-TH1), raised against purified peripheral T cells, and absorbed with an autologous Ig+ line, was shown to bind specifically to T- but not to B-lymphoid cells by both a complement-dependent cytotoxic assay and indirect immunofluorescence. Whereas 90% fetal thymocytes and thymocytes were killed by anti-TH1 and complement, a consistently restricted population (50-60%) of peripheral T cells from several normal donors were lysed, indicating that anti-TH1 is directed against one or more thymus-specific antigens which are lost or reduced on a subpopulation of human T cells in the periphery. Functional analysis of the unreactive (TH1-) and reactive (TH1+) T-cell subclasses demonstrated that TH1- cells mounted a good proliferative response to a battery of specific soluble antigens (mumps, PPD, tetanus toxoid) but neither responded in MLC, nor elaborated LMF in response to tetanus toxoid. In contrast TH1+ cells proliferated in MLC and elaborated LMF but did not respond by 3H-incorporation to soluble antigens. The relevance of these findings to human T-cell functions in vivo and to previously described functional subclasses of murine T cells is discussed.
TL;DR: It is reported that, as a primary step in myogenesis in culture, mononucleated myoblasts undergo a sharp decrease in membrane microviscosity, and shortly afterwards fuse rapidly to form multinucleate myotubes.
Abstract: EMBRYONIC skeletal muscle cell cultures are highly suitable for demonstrating the dynamic role of the plasma membrane in cellular differentiation. A primary event in the overt development of muscle in culture is fusion of the plasma membranes of neighbouring mononucleated myoblasts to form multinucleated myotubes1,2. Previous studies of muscle fusion have focused on ultrastructural3 and electrophysiological4 aspects, the requirement for Ca2+ (ref. 5), and the importance of fusion for the subsequent biosynthesis of muscle-specific proteins5. But, understanding of this process has been hampered by the absence of reliable markers for the initiation of myoblast fusion4. In addition, the importance of the lipid properties of the cell membrane in regulation of the onset of muscle fusion has not been unambiguously demonstrated in spite of the well-established role of lipids in other cases of membrane fusion6. We examined the possibility that fusion of myoblasts is regulated by changes in the lipid fluidity of the cell membrane, as measured by the rotational diffusion of a fluorescent probe. We report here that, as a primary step in myogenesis in culture, mononucleated myoblasts undergo a sharp decrease in membrane microviscosity, and shortly afterwards fuse rapidly to form multinucleated myotubes. The microviscosity remains at a minimal value during the period of rapid cell fusion. The subsequent post-fusional differentiation of the muscle cell is accompanied by the regeneration of membrane rigidity.
TL;DR: The production and partial characterisation of hybrid cell lines with surface antigens characteristic of T lymphocytes are described.
Abstract: THE hybridisation of established cell lines with differentiated cells provides a useful strategy for the production of cell lines having differentiated properties and unlimited growth potential. Clones of these hybrids could be particularly useful in the dissection of cellular interactions of the immune system, a network involving numerous specific cell types which display characteristic ensembles of surface and internal markers. We describe, here, the production and partial characterisation of hybrid cell lines with surface antigens characteristic of T lymphocytes.
TL;DR: These studies demonstrate that analysis of cell specific types of collagen provides a useful method for detailing the specific events in the differentiation of mesenchymal cells in vitro.
Abstract: This work describes an approach to monitor chondrogenesis of stage-24 chick limb mesodermal cells in vitro by analyzing the onset of type II collagen synthesis with carboxymethyl-cellulose chromatography, immunofluorescence, and radioimmunoassay. This procedure allowed specific and quantitative determination of chondrocytes in the presence of fibroblasts and myoblasts, both of which synthesize type I collagen. Chondrogenesis was studied in high-density cell preparations on tissue culture plastic dishes and on agar base. It was found that stage-24 limb mesenchymal cells initially synthesized only type I collagen. With the onset of chondrogenesis, a gradual transition to type II collagen synthesis was observed. In cell aggregates formed over agar, type II collagen synthesis started after 1 day in culture and reached levels of 80-90 percent of the total collagen synthesis at 6-8 days. At that time, the cells in the center of the aggregates had acquired the typical chondrocyte phenotype and stained only with type II collagen antibodies, whereas the peripheral cells had developed into a "perichondrium" and stained with type I and type II collagen antibodies. On plastic dishes plated with 5 X 10(6) cells per 35mm dish, cartilage nodules developed after 4-6 days, but the type II collagen synthesis only reached levels of 10-20 percent of the total collagen. The majority of the cells differentiated into fibroblasts and myoblasts and synthesized type I collagen. These studies demonstrate that analysis of cell specific types of collagen provides a useful method for detailing the specific events in the differentiation of mesenchymal cells in vitro.
TL;DR: The Ly and Ia phenotypes of T lymphocytes involved in the in vitro generation of helper and suppressor cells were identified and the precursors of both cells are found in adult thymectomized spleen.
Abstract: The Ly and Ia phenotypes of T lymphocytes involved in the in vitro generation of helper and suppressor cells were identified. The precursors of both cells are found in adult thymectomized spleen. Helper precursors are Ly-1+2-3-Ia-, while suppressor precursors are Ly-1-2+3+Ia-, although the suppressor effector is Ia+. In both cases a second 'amplifier' cell is required for differentiation of precursors to occur. This cell is found in anti-lymphocyte serum-treated spleen and has the phenotype Ly-1+2+3+Ia-.
TL;DR: Highly differentiated cells are conceptually relatively simple systems—at least, in terms of quantification of synthesis and accumulation of the characteristic protein products and their mRN A templates, and it is confident that such quantifications will soon enable us to infer at what levels of information flow differential gene expression is controlled in particular systems.
Abstract: Cell differentiation is the consequence of differential gene expression in space and in time. Differential expression in turn depends on cellular differences, initially established through inheritance of non-chromosomal, cytoplasmic determinants from a polarized progenitor, or through interactions with neighboring cells. Determination, the process of setting up and maintaining the control mechanisms underlying differential gene activity, is obviously of ultimate biological interest. Although a molecular description of determination in eukaryotes is beyond our present grasp, a rigorous biochemical description of differential gene expression is certainly possible. This is easiest with highly differentiated cells, i.e., with cells which, at some point in their life, become specialized for the large-scale production of one or a few cell-specific protein products. Their methodological advantages have been enumerated elsewhere (Kafatos, 1972a). Highly differentiated cells are conceptually relatively simple systems—at least, in terms of quantification of synthesis and accumulation of the characteristic protein products and their mRN A templates. We can be confident that such quantifications will soon enable us to infer at what levels of information flow differential gene expression is controlled in particular systems. We suspect that highly differentiated cells may be simple in another, even more fundamental sense: production of “luxury” proteins (those not required for maintenance) may be devoid of a whole intricate network of homeostatic regulation.