Showing papers on "Transdifferentiation published in 1991"

Basic fibroblast growth factor induces retinal pigment epithelium to generate neural retina in vitro.

Abstract: During embryogenesis, the cells of the eye primordium are initially capable of giving rise to either neural retina or pigmented epithelium (PE), but become restricted to one of these potential cell fates. However, following surgical removal of the retina in embryonic chicks and larval amphibians, new neural retina is generated by the transdifferentiation, or phenotypic switching, of PE cells into neuronal progenitors. A recent study has shown that basic fibroblast growth factor (bFGF) stimulates this process in chicks in vivo. To characterize further the mechanisms by which this factor regulates the phenotype of retinal tissues, we added bFGF to enzymatically dissociated chick embryo PE. We found that bFGF stimulated proliferation and caused several morphological changes in the PE, including the loss of pigmentation; however, no transdifferentiation to neuronal phenotypes was observed. By contrast, when small sheets of PE were cultured as aggregates on a shaker device, preventing flattening and spreading on the substratum, we found that a large number of retinal progenitor cells were generated from the PE treated with bFGF. These results indicate that bFGF promotes retinal regeneration in vitro, as well as in ovo, and suggest that the ability of chick PE to undergo transdifferentiation to neuronal progenitors appears to be dependent on the physical configuration of the cells.

Morphological development and fate of the mouse mesonephros.

Abstract: A study has been made of the development of mesonephric tubules in the mouse to investigate the possible transdifferentiation of tubule epithelial cell to gonadal somatic cells and/or adrenal cortical cells. Immunohistochemical localisation of laminin was carried out to study the development of basal laminae. Cells at the ventral aspect of mesonephric tubules did not show an epithelial phenotype during the period of somatic cell population of the gonadal blastema; a basal lamina appeared ventrally only after this period. Therefore, it is not necessary to postulate transdifferentiation of these cells.

Episome-generated N-myc antisense RNA restricts the differentiation potential of primitive neuroectodermal cell lines.

Abstract: Neuroectodermal tumors of childhood provide a unique opportunity to examine the role of genes potentially regulating neuronal growth and differentiation because many cell lines derived from these tumors are composed of at least two distinct morphologic cell types. These types display variant phenotypic characteristics and spontaneously interconvert, or transdifferentiate, in vitro. The factors that regulate transdifferentiation are unknown. Application of antisense approaches to the transdifferentiation process has allowed us to explore the precise role that N-myc may play in regulating developing systems. We now report construction of an episomally replicating expression vector designed to generate RNA antisense to part of the human N-myc gene. Such a vector is able to specifically inhibit N-myc expression in cell lines carrying both normal and amplified N-myc alleles. Inhibition of N-myc expression blocks transdifferentiation in these lines, with accumulation of cells of an intermediate phenotype. A concomitant decrease in growth rate but not loss of tumorigenicity was observed in the N-myc nonamplified cell line CHP-100. Vector-generated antisense RNA should allow identification of genes specifically regulated by the proto-oncogene N-myc.

Transdifferentiation : flexibility in cell differentiation

Abstract: Introduction Are dormant genes in differentiated cells activated? Does change in differentiated cell phenotypes occur in normal development? Examples of transdifferentiation among single or related cell classes Re-evaluation of classical examples of metaplasia and some related systems Does transdifferentiation occur in regeneration? Transdifferentiation in cell culture conditions Factors influencing transdifferentiation Characteristics of the transdifferentiation process References.

Common mechanisms of retinal regeneration in the larval frog and embryonic chick.

Abstract: Amphibians and embryonic chicks possess the ability to regenerate retinal neurons by the transdifferentiation of pigment epithelium into neuronal progenitors. Recent studies have begun to identify the molecular factors involved in this process. Laminin (a component of the extracellular matrix) has been shown to be important in the process of retinal regeneration in the larval frog both in vitro and in vivo and basic fibroblast growth factor (bFGF) stimulates the same process in chicks in vivo. To determine the mechanisms by which these factors induce retinal regeneration we studied their effects on cultured chick pigment epithelium cells. bFGF was added to enzymically dissociated chick embryo pigment epithelial cells plated at several different densities on various substrates including laminin. We found that bFGF stimulated proliferation but although the cells lost pigmentation and demonstrated distinct morphological changes, no definitive transdifferentiation could be demonstrated using several neuron-specific antibodies as markers. When the pigment epithelium was cultured as aggregates on a shaker device which prevented flattening and spreading on the substrate a large number of retinal progenitor cells were generated from the pigment epithelium treated with bFGF. The ability of chick pigment epithelium to undergo transdifferentiation thus appears to be dependent on the physical configuration of the cells.

Short term retinol treatment in vitro induces stable transdifferentiation of chick epidermal cells into mucus-secreting cells.

Abstract: Epidermal mucous metaplasia of cultured skin can be induced by treatment with excess retinol for several days (Fell 1957). In the induction of mucous metaplasia, retinol primarily affects the dermal cells and retinol-pretreated dermis can alter epidermal differentiation towards secretory epithelium (Obinata et al. 1987). In this work, we found that mucous metaplasia could be induced by culturing 13-day-old chick embryonic tarsometatarsal skin in medium containing retinol (20 μM) for only 8-24 h, followed by culture in a chemically defined medium (BGJb) without retinol or serum for 6 days. The application of cycloheximide together with retinol during the first 8 h of culture inhibited epidermal mucous metaplasia during subsequent culture for 6 days in BGJb, indicating that induction of a signal(s) in the dermis by excess retinol requires protein synthesis. However, the presence of 20 nM hydrocortisone (Takata et al. 1981) throughout the culture period did not inhibit retinol-induced epidermal mucous metaplasia of the epidermis. This indicates that a brief treatment of the skin with excess retinol determines the direction of epithelial differentiation toward secretory epithelium; this is a simpler in vitro system for the induction of epidermal mucous metaplasia than those established before.

Molecules specific to pigment epithelial cells: expression during in situ development and in vitro lens transdifferentiation of chick embryo pigment epithelium

Abstract: The retinal pigment epithelium (PE) is a monolayer of cells and plays a vital role in the regulation of the neural retina. We prepared monoclonal antibodies directed against retinal PE cells to analyze the specificity and differentiation of these cells. Spleen cells from BALB/c mice immunized with chick embryo retinal PE cells were fused with myeloma cells. Seven independent monoclonal antibodies were obtained which specifically recognized PE cells but did not react with any other tissues examined. None of the monoclonal antibodies reacted with the choroid and skin of pigmented chicks, suggesting that these antigens were unrelated to melanogenesis. Two of the 7 antibodies reacted with the PE cells in the retina, ciliary body and iris; the remaining 5 antibodies were specific to the PE cells in the retina. In the process of in vitro lens transdifferentiation from PE cells, the distribution of an antigen detected by one monoclonal antibody changed from the cytoplasmic granules to the actin fibers and then its immunoreactivity declined. The other monoclonal antibodies did not react with the differentiated PE cells and transdifferentiated lens cells, suggesting that the antibodies might be specific to the PE cells in the differentiated state, both in vivo and in vitro. During the in situ developmental process, each monoclonal antibody began to be immunoreactive to future PE cells in the optic eye cup at various stages from 72 to 120 h. The molecules common to all types of PE cells were expressed earlier than those specific to PE cells of the retina. Future ciliary and iridial PE cells appeared to transiently express the molecules specific to the retinal PE cells before the tip of eye cup contacted the lens vesicle. These data suggest that the monoclonal antibodies established in this study are powerful probes for exploring the functions and differentiation of PE cells.

Ageing in the chick lens: in vitro studies.

Abstract: In principle, ageing may be due to the interaction of several factors, including the accumulation of random changes both genomic and non-genomic, secondary changes in a tissue contingent upon the changing function of other tissues, and programmed non-random changes in the tissue-specific expression of various genes. The use of a single tissue comprising one cell type only, in which the major gene products are well defined, in which there is a well attested series of developmental and age-related changes in cell properties and gene expression and which can be studied and compared in vivo and in vitro, offers advantages for investigation of these questions. The vertebrate eye lens possesses these advantages. The crystallins (proteins expressed at super-abundant levels in the lens) are well characterised. The lens epithelial cells (LEC) grow readily and can differentiate into the lens fibre cells in vitrom, and, finally, such terminally differentiated cells may also be derived, by a process of transdifferentiation, from neural retina cells (NRC) in vitro. Thus the effect on ageing changes of the tissue of origin may also be studied. This article reviews our previous studies on long-term changes in growth potential, differentiation capacity and crystallin expression of chick lens cells in ageing cultures, their overall similarity to events in vivo and the effect on ageing changes of genotypes affecting the growth rate. It presents new information on these genetic aspects, and on crystallin expression in long-term ageing cultures of transdifferentiated neural retina, and compares the behaviour of ageing chick lens cells with that reported for mammals.

Effects of tumor promoters and diacylglycerol on the transdifferentiation of striated muscle cells of the medusa Podocoryne carnea to RF-amide positive nerve cells

Abstract: Isolated striated muscle of the anthomedusa of Podocoryne carnea can be stimulated to carry out DNA synthesis and transdifferentiation to RF-amide positive nerve cells by the protein kinase C-activating drugs 12-O-tetradecanoyl-13-acetate (TPA), mezerein and diacylglycerol. Methylether-TPA, which does not activate protein kinase C, is unable to induce transdifferentiation. In isolated muscle tissue treated simultaneously with TPA and K-252a, an inhibitor of protein kinase C, the rate of transdifferentiation is greatly reduced. The role of protein kinase C in transdifferentiation is discussed.

Replicative culture in vitro of pancreatic epithelial oval cells derived from rats after copper deficiency-induced acinar cell depletion

Abstract: Procedures for the isolation and in vitro maintenance of oval (periductular) cells obtained from pancreas of rats maintained on copper-deficient diet for 8 wk are described. Oval cells grew readily in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum, and have been continuously propagated in culture for 6 mo. through 10 passages. Morphologically, these cells showed epithelial features characterized by frequent cell junctions, microvilli, intermediate filaments, and attempted lumen formation. These cells were negative for y-glutamyltranspeptidase but stained positively with OV-6 antibodies. Chromosomal analysis revealed hyperdiploid pattern with a model number of 68. These pancreatic oval cells of rat pancreas should serve as a valuable tool for establishing subcloned cell lines for the study of transdifferentiation and in establishing the stem-cell potential.

Regenerative capacity of retinal cells and the maintenance of their differentiation.

Abstract: Mechanisms underlying cell type stability and the capacity of retinal cells for transdifferentiation are discussed It is shown that cells of amphibian pigmented epithelium can be transformed into retina or lens cells depending on the inducing cell type: the influence of retina enables them to be transformed into retina, the influence of lens epithelium, to lens cells (lentoids or lenses) This led to an attempt to discover the molecular character of cell action by means of transfilter induction in early gastrula ectoderm of Xenopus laevis The results show that the induced cell types correspond to the main inducing cell type, around which a range of neighbouring cell types is produced; this has been shown for five different cell types The inducing factors involved seem to show qualitative differences It is probable that they play a stabilizing role in the maintenance of the differentiated state of tissues, since temporary dissociation into cells leads eye tissues to transdifferentiate into other types Such molecular factors can play a significant role in the maintenance of the type of differentiation and also in conversion into other cell types These mechanisms of maintenance are not restricted to interactions between molecules and cells, since membranes on the surface of the retina and pigmented epithelium contribute to their shaping and consequently to the stability of the cell type