Showing papers on "Transdifferentiation published in 1984"

Goblet cell density and vascularization during conjunctival transdifferentiation.

Abstract: After debridement of the entire corneal epithelium with n-heptanol, two groups of rabbit corneas were segregated according to the extent of corneal neovascularization. Using a new topographic goblet-cell counting method and routine histology, the authors have reexamined the process of conjunctival transdifferentiation and compared the changes of goblet-cell density and morphology between nonvascularized and vascularized groups for a follow-up period of 167 days. Analysis of the total goblet-cell density disclosed that no goblet cells appeared on the corneal surface during the entire period of reepithelialization. After that, two phases were identified with respect to goblet-cell density: phase I (day 0-17) and phase II (after day 17). In phase I, both groups had a similar surge of goblet cells, with the peak occurring between days 7 and 11, suggesting little correlation with vascularization. Morphologic studies indicated the presence of a prominent centripetal cellular migration. In phase II, the nonvascularized group showed a rapid decline in goblet-cell density, and as a result the morphologic transdifferentiation into a cornea-like epithelium was completed on day 43. The changes of goblet cells to a smaller size and the presence of a more acidic mucin in the centrifugal receding zone, suggested that transdifferentiation on nonvascularized corneas is a process involving changes of cellular differentiation. In contrast, the vascularized group maintained a high plateau of goblet-cell density and an epithelium with conjunctival characteristics until day 167. This result disclosed that retardation of conjunctival transdifferentiation by corneal vascularization was in phase II. The possible role of vascularization in the modulation of conjunctival transdifferentiation is discussed. Invest Ophthalmol Vis Sci 25:1168-1176, 1984

Induction of muscle genes in neural cells

Abstract: The regulation of skeletal muscle genes was examined in heterokaryons formed by fusing differentiated chick skeletal myocytes to four different rat neural cell lines. Highly enriched populations of heterokaryons isolated using irreversible biochemical inhibitors were labeled with [35S]methionine and analyzed on two-dimensional gels. Rat skeletal myosin light chains were induced in three of the four cell combinations. The one exception, the S-20 cholinergic cell line, not only failed to synthesize rat muscle proteins but also suppressed chick myogenic functions. Experiments with heterokaryons between chick myocytes and cells from whole embryonic rat brain cultures demonstrated that rat skeletal myosin light chains are inducible in normal diploid neural cells as well as in established neural cell lines. In contrast, dividing cell hybrids between rat myoblasts and rat glial cells were nonmyogenic. These results demonstrate that although neural cells may contain factors that prevent the decision to differentiate along myogenic lines in cell hybrids, most neural cell lines do not dominantly suppress the expression of muscle structural genes in heterokaryons. Furthermore, the skeletal myosin light chain genes in most neural cell lines are regulated by a mechanism that permits them to respond to putative chick skeletal myocyte-inducing factors. The "open" state of these myogenic genes may explain many of the reports of apparent "transdifferentiation" to muscle in neural cultures and neural tumors.

Factors affecting DNA synthesis in an in vitro system.

Abstract: Mononucleated striated muscle cells and one type of endoderm can be isolated from anthomedusae and cultivated in artificial sea-water. In the cultivated muscle the differentiated state is maintained. In the cultivated endoderm flagella are formed, but no new cell types differentiate and DNA synthesis or mitosis is not observed. When isolated muscle is grafted upon endoderm, regeneration or formation of new cell types is not observed. Following treatingment with bacterial collagenase DNA synthesis and flagellum formation are initiated in the isolated muscle; in the isolated endoderm, collagenase treatment has no effect. When striated muscle treated with collagenase is grafted upon endoderm, DNA synthesis is observed in the endoderm, and a regenerate is formed involving transdifferentiation. Although desmosomal contact between collagenase treated muslce and the endoderm is established, it is not sufficient to induce DNA synthesis; complete covering of the endoderm by the muscle is required.

Expression of Toxin Receptors on Cell Surfaces in Transdifferentiating Cultures of Neural Retina

Abstract: It has often been asked which of the cell types found during the early stages of culturing embryonic chick neural retina can undergo transdifferentiation into lens in vitro. Since neuronal cell-surface toxin receptors are maintained in NR cultures for much longer than internal neuronal enzymes (e.g. choline acetyltransferase), and since the transdifferentiation process can be greatly accelerated by preparing reaggregates of neural retina cells after about 10 days of preculture as “monolayers”, a direct test of this question became feasible. 7 or 9 day embryonic chick neural retina cells, precultured for 10-1 2 days as monolayers, were dissociated and reaggregated under continuous gyration. Reaggregates were maintained for 8 days in the presence of either tetanus toxin or FITCconjugated a-bungarotoxin, to permit surface-bound toxins to become internalised via receptor turnover. The reaggregates were then dissociated, stained with rabbit antitoxin and FITC-conjugated anti-antibody in the case of tetanus toxin-labelled material, and restained with a rat or mouse antibody against chick 6 crystallin followed by the appropriate rhodamine-conjugated anti-antibody. Although both FITC/toxin-labelled cells (putative neurones) and rhodamine/d crystallin-labelled cells (transdifferentiated lens cells) were abundant, no examples of double-labelled cells were observed with 9 day starting material, and only a very few with 7 day starting material. We conclude that the vast majority of differentiated neuronal cells expressing surface receptors for these toxins do not transdifferentiate directly into lens cells.

Mechanisms of transdifferentiation and their relation to induction and competence

Abstract: The ways of transdifferentiation are considered: spontaneous and induced. Spontaneous transdifferentiation taking place after the disaggregation of cells in the clonal and cell cultures is determined by the competence of the transforming cells themselves. Induced transdifferentiation is determined not only by the competence but also by the effect of external inducing factors. It is suggested that the direction of induced transdifferentiation depends on the ratio between the external and internal inducing factors and on the character of cell cycles. It is probable that the inducing factors entering the cells during the early embryonic induction are reproduced in the cells in a dormant state and some of them do not reveal their presence until appropriate conditions are set. When the cells are isolated in the cultures, the ratio of these factors inside the cell changes and a competence to transdifferentiation is revealed which arises as early as during induction.

Transdifferentiation and survival of neural retina cells in relation to illumination.

Abstract: Cultures of chicken embryo neural retina cells were exposed to light of different intensities and colours, in order to identify the wavelengths that promote cell degeneration and transdifferentiation into pigment epithelium. Blue and green light caused cell death; blue, green and yellow light enhanced transdifferentiation; red light had no effect. The relevance of these findings to retinal degeneration in man and the possible mediation of rhodopsin, riboflavin and other chromophores are discussed.