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Biomedical subjects

G V Lopashov

Publications and source records attributed to G V Lopashov.

At least 19 recordsLinked to original sources
PubMed2005

Inductive characteristics of proteins secreted by retinal cells.

The studies of the development of eye rudiments and formation of adult eye tissues have always been among priorities in developmental biology and then in developmental genetics, which is associated with the peculiarities of the development and structure of the eye. In the late 80s, it was established by the group of developmental factors of the Institute of Gene Biology of RAS that many differentiated tissues are able to produce proteins causing homologous differentiations in polypotent cells of early gastrula ectoderm. The aim of our present study was isolation of proteins secreted by mammalian and fish retinal cells and determination of their inductive properties in early gastrula ectoderm of Xenopus laevis. The sets of proteins secreted by retina induce tissues homologous to the inducer, that is, neural tissue, brain, retina, pigmented epithelium, and also lenses and ear vesicles. The retinal inductive proteins retain their homologous inductive capacity after lyophilization. Biological testing shows that a total mixture of proteins secreted by retinal cells induces in polypotent gastrula ectoderm of X. laevis a narrower spectrum of tissues than the fractions obtained from this mixture. The above-outlined results obtained in thecourse of investigations of inductive peculiarities of retina and its fractions help in the elucidation of questions concerning embryonic induction and factors determining it, as well as questions concerning the maintenance of tissue specifity and regenerative capacity of the tissue studied.

Animals↗
PubMed2000

[Isolation and effects of inducing factors secreted by the lens epithelium cells].

Our previous studies showed that, unlike tissue extracts, the cells of living organs secrete substances capable of inducing the same organ rudiments in the early gastrula ectoderm (EGE). In this work, the molecular nature of these substances was studied. The porcine lens epithelium was chosen for the initial analysis. When cultivated, this epithelium secreted a mixture of proteins, which were separated by gel-filtration. Both the total protein mixture and its individual fractions were tested for their inducing capacity using the early gastrula ectoderm of Rana temporaria. Unexpected results were obtained, which indicated that (a) the mixture of native proteins secreted by lens epithelium has a selective inducing capacity differing from those of individual fractions isolated from this mixture and (b) each fraction has a specific effect, but all of them cause the induction of neural tissue or sensory organs. These results (obtained for the first time) suggest that the inducing capacity of individual protein fractions is wider than that of the total protein mixture secreted by lens epithelium. This fact raises a question concerning the relationships between the mechanisms underlying the corresponding inducing effects.

Animals↗
PubMed1997

Inductive capacity of living eye tissues from adult frogs.

The aim of the present work has been to demonstrate the inducing capacity of living homogenous undamaged tissues from adult frogs. Tissues from the eyes of adult frogs Xenopus laevis: retina (R), pigmented epithelium (PE), lens epithelium (LE), and the forebrain (B) as a control, were tested for their inducing capacity using early gastrula ectoderm. To exclude the possibility of ad-mixture of inducing cells in early gastrula ectoderm the transfilter induction technique was used throughout. The results show that the tissues used in the cases of most intense induction tended to induce similar cell types: both R and PE induce R + PE together with adjoining neural cells and secondary lens cells. LE induces lentoids (L) and B cells induce neuroids. In each case epidermis surrounds the explants filled with ectomesenchyme (EM) and melanophores (M). Immunofluorescence reactions clarified the nature of lens cells. This discovery indicates that cells of adult tissues continue throughout life producing substances which are able to promote the appearance of cells of the same type during development. Probably they also serve to mediate interrelations between cells of these tissues, regulating the stability of their differentiation in the adult state, as well.

Age Factors↗
PubMed1997

Hierarchy of inductive events.

Examination of data on the inducing capacity of mesoderm-inducing factors shows that none of them induces mesoderm alone, but that they also induce endoderm and neural tissues, while in the mesoderm itself, they induce tissues belonging to its main levels. Tests on the inducing capacity of living retina have shown that it does not induce mesoderm, but does induce a spectrum of tissues, including retina, pigmented epithelium, lens and a piece of brain. This situation seems to be indispensable because if it evokes only one differentiation, an increase of diversity in development would be impossible. Selectivity occurs only at the end of the sequence of inductions, as it does in the induction of lens tissue by lens epithelium. Such mechanisms, however, are insufficient for the development of different kinds of cells into homogeneous tissues. This is achieved through the aggregation or separation of initially induced cells, their own products determining (or not) their further fate and leading to homogeneity of tissues. These mechanisms of the first two levels of inductive interactions overlap with events that allow or prevent the access of inducing factors and are, therefore, also involved in the manifestation of competence of potentially reactive cells.

Animals↗
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↗