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G V Lopashov

Publications and source records attributed to G V Lopashov.

14 recordsLinked to original sources
PubMed1991

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

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.

Animals↗
PubMed1983

Transdifferentiation of pigmented epithelium induced by the influence of lens epithelium in frogs.

The influence of lens epithelium (LE) of adult frogs on the character of transdifferentiation of retinal pigmented epithelium (RPE) of adult frogs and tadpoles of Rana temporaria has been studied. After a period of intense proliferation RPE cultured in vivo in contact with LE in the tadpole orbit almost exclusively transforms into retina. RPE precultivated in vitro in contact with LE for three days in protein-free medium does not manifest cell divisions and mostly transdifferentiates into lentoids. The problem of the relative significance of inducing determinants and the role of activation or inhibition of proliferation in transdifferentiation is discussed.

Aging↗
PubMed1978

Developmental approaches to organ restoration.

This paper discusses the problem of applying the achievements of developmental biology to organ restoration. Experiments on artificially induced transdifferentiation as a prerequisite for organ restoration are reviewed. The advantage of using cells that start differentiation from the dedifferentated state is that they can participate in the construction of new organs. However, cell transdifferentiation is not sufficient for biomedical purposes, since the problem of construction of typically formed organs--namely, the morphogenesis of groups of differentiating cells--remains to be solved. Data, where a partial approach to typical organ restoration has been achieved are analysed. This serves as a tentative step in the application of developmental-biological approaches to the problem of organ restoration.

Amphibians↗
PubMed1974

[Cellular heredity, its alteration and organ restoration].

Patterns of cell heredity in vertebrates and possibility of its alteration, i. e. artificial tissue metaplasia, are considered. These problems are compared with the well studied phenomenon of metaplasia in eyes of the newt in which the removal of some parts of the eye leads to natural metaplasia, an initial step for restoration of eye parts. A brief analysis of sequence of inductive processes in development shows that by the end of the period of induction and the onset of terminal differentiation the maximum concentration of specific inducing agents in induced rudiments can be expected. This suggestion was confirmed by the experiments of specific assimilatory induction in gastrula ectoderm and artificial conversion of pigmented epithelium in retina and lens tissues. On the basis of the data reported and in comparison with the theories of intragenomic regulation, a new hypothesis of cell heredity is put forward. The basic idea of this hypothesis is that the regulatory genes can switch on the genes responsible for the synthesis of terminal proteins via inducing proteins; the latter can simultaneously programm the function of regulatory genes, initiating their own synthesis. Due to such a feedback mechanism forming during development, stable cell types arise. Their inheritance can be altered by the introduction of new inducing agents in parallel with the elimination of conditions stabilizing cell differentiation. Possible ways for application of artificial metaplasia for restoration of eye defects in medical practice are considered.

Animals↗
PubMedDate not supplied

[Inductive effect of the eye tissues of adult clawed toads on the gastrula ectoderm].

The inducing influence of adult eye tissues on the early gastrula ectoderm was studied in vitro. Both retina and pigment epithelium induced in the early gastrula ectoderm similar spectra of cell types, including nervous tissue, retina, pigment epithelium, lentoids, ectomesenchyme, and melanophores. It is suggested that the correspondence of these cell types with those arising at a spontaneous transdifferentiation of the isolated retina and pigment epithelium cells in vitro or at the induction of the early gastrula ectoderma by archencephalic endomesoderm during the normal development can be accounted for by that in these eye cells molecular determinants appeared as a result of induction and maintaina the stability of their differentiation and their potencies to transdifferentiation in vitro being reproduced during the lifetime of these cells.

Animals↗
PubMedDate not supplied

[Mechanisms of transdifferentiation and their relation to induction and competence].

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.

Animals↗