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A T Mikhailov

Publications and source records attributed to A T Mikhailov.

At least 19 recordsLinked to original sources
PubMed2001

Consequences of the Spemann-Mangold organizer concept for embryological research in Russia: personal impressions.

The impact of the organizer concept on Russian experimental embryology is shortly reviewed. Attempts to study embryonic induction in Russia may be grouped into embryological and biochemical approaches. This paper provides a framework for, and overvalue of, the contributions of Russian biologists to the problem of embryonic induction. Two model systems--lens and neural inductions--are of special significance to modern developmental biologists. Moreover, the study of eye lens induction actually gave rise to research on developmental mechanics in Russia. This was one of the reasons why we limited this article to these two model systems. After retrospective consideration of the results of the search for possible lens-inducing factor candidates, the discussion turns towards some of the examples of neural-inducing agents detected in embryonic tissues and the new questions raised by the progress that has been made in the analysis of the Spemann-Mangold organizer.

Animals↗
PubMed2000

Carboxylesterases moonlight in the male reproductive tract: a functional shift pivotal for male fertility.

This essay addresses the carboxylesterase redundancy in the male reproductive tract seemingly conserved across phyla. Evidence is provided which suggests that carboxylesterases are recruited by the male reproductive system in certain animal groups. These provide advantageous metabolic capabilities to sperm protection, sperm maturation, and sperm use. Rather than an archival record of the available data, we seek possible answers to the central question: Why is carboxylesterase over-expression adaptive with the functioning of the male reproductive tract with respect to male fertility? We discuss patterns of carboxylesterase over-expression and accumulation in different compartments of the male reproductive tract. We also provide evidence of how these patterns are associated with a long sperm path to egg through different local effects. The hyper-expression of carboxylesterases can play different physiological roles depending on its localization in the male reproductive system. However, all the "acquired" functions can serve the same purpose; creating conditions which maximize the fertilizing potential of the sperm. To confirm our concept and more clearly illuminate "moonlighting" roles of carboxylesterases in the male reproductive tract, requires a more extensive comparative analysis of a variety of carboxylesterases in a larger number of species.

Carboxylesterase↗
PubMed2000

Frog lim-1-like protein is expressed predominantly in the nervous tissue, gonads, and early embryos of the bivalve mollusc Mytilus galloprovincialis.

In a few well-known cases, the biological consequences of the disruption of lim-1 homeodomain (HD) genes have demonstrated the important roles of these genes in vertebrate development, especially in the nervous tissue, kidney, and gonads. Functional assay approaches require information not only about lim-1 gene organization, but also about properties and tissue localization of Lim-1 proteins. Although lim-1 genes have been identified in certain phyla of invertebrates, no information is available on Lim-1 proteins and genes in bivalve molluscs. Our study represents the beginning stage of identification of the Lim-1-related proteins in marine bivalves. Using antibodies against the C-terminal region of the Xenopus laevis Lim-1 protein, we describe cross-reactive antigen patterns in adults and early embryos of the mussel Mytilus galloprovincialis, as well as in sea urchin and chick embryos. In adult mussels, nervous ganglia and gonads display the most prominent Lim-1 immunoreactivity. Further, the antibodies verified the prediction that mussel Lim-1 antigens, like Lim-1 HD proteins in general, can be localized in the nucleus. Moreover, antibody detection allowed us to identify the Lim-1-like antigens in unfertilized mature eggs, as well as in very early embryos of bivalve molluscs and sea urchins (Strongylocentrotus purpuratus). In mussel eggs and embryos, Lim-1 antigens are expressed in multiple forms (40, 45, and 65 kDa), as detected by SDS-PAGE followed by Western blot. Taken together, the observations emphasize the conservation of the Lim-1 protein expression pattern in the nervous tissue and gonads of different animal groups, and demonstrate that Lim-1-like polypeptides can be maternally accumulated in eggs and, therefore, are present in very early embryos before zygotic expression of the genes begins.

Amino Acid Sequence↗
PubMed1999

Carboxylesterase overexpression in the male reproductive tract: a universal safeguarding mechanism?

Data on expression patterns of carboxylesterases in the male reproductive tract of different animal groups (i.e. bivalve mollusks, fruitflies and rodents) are summarized to highlight some particularly interesting questions in the context of sperm differentiation, maturation and function. The male reproductive system, in spite of extreme variation in the anatomical/morphological organization in different species, is characterized by similar patterns of male-dependent carboxylesterase overexpression. The phenomenon of conserved carboxylesterase overexpression indicates similar male sex-associated functions of the enzymes. There is possible evidence of carboxylesterase recruitment by male reproductive-tract tissues indicating that it could be adaptive for spermatogenesis, sperm maturation and sperm use. Moreover, this idea can be extended to include a sperm cell lineage protection. This issue is discussed in the light of recent data on environmental reproductive xenobiotics that can provide a basis for a hypothetical explanation of carboxylesterase overexpression in the male reproductive tract. Based on a well-known role of carboxylesterases in detoxification of environmental chemicals such as organophosphate pesticides, it is proposed that various male genital tract carboxylesterases may be characterized by a similar physiological function to protect the male reproductive system against xenobiotic influences that could provoke its dysfunction, thus altering sperm differentiation and maturation.

Amino Acid Sequence↗
PubMed1998

Male-associated polypeptide (MAP) expression in different compartments of the reproductive system of the mussel Mytilus galloprovincialis: immunocytochemical and western blot study.

Mytilus mussels are characterized by annually repeated reproduction which is associated with subsequent growth, morphogenesis, breakdown and redevelopment of the gonad and reproductive tract into mantle mesenchyme. We present a description of the expression of the male-associated polypeptide (MAP; see Mikhailov et al. 1995) in different compartments of the male reproductive system as well as in mantle gonad-supporting tissue. MAP is expressed in both gonad and mantle structures in dynamic patterns that show a substantial overlap in terms of dependence on the stage of gonad development/involution. In general, the total MAP concentration directly correlates with the volume of gonad tubule/duct structures but inversely correlates with mantle connective tissue cell fraction. A maximum of MAP expression is reached in the fully ripe male gonad. MAP is localized around gonad tubules/ducts, in the gonoduct epithelium, membranes of follicle-like structures as well as in the extracellular fiber-like structures of the mantle. However, we also demonstrate unique sites of MAP accumulation in the lumen of gonad follicle-like tubules and in ductal fluid. The latter is characterized by a very high MAP concentration. MAP is also detected in sperm-containing cell suspension obtained by gonad biopsy which we interpret as a result of the adsorption of MAP on mature spermatozoa. The results obtained should be taken into consideration in the interpretation of possible MAP functions since they seem to point to MAP as a major component of ductal (seminal) fluid of the male reproductive tract. It is likely that MAP is able to complement the processes of sperm terminal differentiation and maturation. In addition, we demonstrate that the male-predominant character of MAP expression is restricted by gonad-containing tissues (i.e., mantle and visceral mass) only, although the polypeptide is also detected in other somatic organs in both males and females.

Animals↗
PubMed1997

Male-predominant carboxylesterase expression in the reproductive system of molluscs and insects: immunochemical and biochemical similarity between Mytilus male associated polypeptide (MAP) and Drosophila sex-specific esterase S.

We suggested that sexual differentiation of the reproductive system in gonochoric species of invertebrates can be characterized by common molecular mechanisms in spite of high morphological divergences of reproductive tract organs in different animal groups. The present study focused on this problem and report our observations on biochemical characteristics of male-associated polypeptide (MAP) identified in the gonad tissue of bivalve molluscs, Mytilus galloprovincialis, in comparison to those of male-specific carboxylesterase (esterase S) of Drosophila virilis ejaculatory bulbs. We provide evidences for the immunochemical similarity of Mytilus MAP and Drosophila esterase S. We also show that MAP is characterized by esterase activity toward both, alpha- and beta-naphthyl acetates. Using immunofluorescence, we found MAP in the gonad (mantle) connective tissue, membranes of follicles and around gonad ducts but not in sperm cells. Nevertheless, the levels of MAP expression depend on presence or absence of ripe spermatozoa in the gonad follicles. In mature gonads before spawning, MAP is expressed at high level, while in the spent gonads only traces of this polypeptide could be detected. Using Western immunoblot, MAP was not observed in spermatozoa obtained by biopsy of gonad follicles. In contrast, we found this protein in spawned sperm cells. Thus, we suggest that spawning may be required to establish the trafficking mechanisms that control whether MAP is retained or excreted by the gonad. Taken together, the results indicate that MAP of M. galloprovincialis is structurally and functionally related to esterase S of D. virilis ejaculatory bulbs.

Amino Acids↗
PubMed1997

Developmental patterns of crystallin expression during lens fiber differentiation in amphibians.

Data on activation of crystallin synthesis during lens fiber (LF) formation in amphibians are summarized to point out the questions particularly interesting in the context of lens cell lineage-specific expression programming under different developmental conditions. LFs are known to differentiate throughout life along the same pathway that includes at least five compartments. Using the amphibian eye lens as a model, we have studied how crystallins are expressed in the course of: (1) embryonic LF formation, (2) LF differentiation in adults, and (3) LF transdifferentiation from other (non-lens) eye tissues. Our experiments showed that synthesis of crystallins during morphologically similar LF differentiation in embryonic and adult amphibian lens has different spatial-temporal patterns (i.e., is apparently activated according to different programs). Certain results obtained in our studies suggest the absence of any direct relationship between the capacity of adult newt iris cells to transdifferentiate into LFs and crystallin synthesis (< > to such transdifferentiation) in them. Crystallins appear at the advanced stages of iris transdifferentiation into the lens and dynamics of their synthesis in the < > lens resembles that in the embryonic lens, although a new lens rudiment develops from the adult iris epithelium. Data on alternative patterns of the crystallin gene activation are summarized and compared with recent observations on spatial-temporal expression of Pax genes, which play an essential role in lens cell commitment and crystallin synthesis. On this basis, it is suggested that ontogenetic and tissue- or cell-specific changes in Pax gene expression may result in altered programs for activation of crystallin genes in embryonic, adult, and regenerating lens.

Animals↗
PubMed1995

Sexual differentiation of reproductive tissue in bivalve molluscs: identification of male associated polypeptide in the mantle of Mytilus galloprovincialis Lmk.

We have addressed the question of sexual reproductive tissue dimorphism in bivalve molluscs, Mytilus galloprovincialis Lmk, which is a stable gonochoric species although with no apparent differences in gonad morphology of both sexes. At all periods of the annual cycle the proteins specific of male/female gonads were identified. One of these proteins, "male-associated polypeptide" with apparent MW 39 kDa (MAP-39), has been biochemically and immunochemically characterized. MAP-39 concentration in male mature gonads achieved up to 10% of the total soluble protein while in female ones only traces of this protein could be detected. In male mantle, MAP-39 expression was associated with the process of gonad development and maturation as well as gamete spawning, although this polypeptide has been localized in fibroblast-like cells, membrane of follicles and connective tissue matrix of the mantle but not in germinal cells.

Animals↗
PubMed1995

Partially purified factor from embryonic chick brain can provoke neuralization of Rana temporaria and Triturus alpestris but not Xenopus laevis early gastrula ectoderm.

A high neuralizing activity has been determined in forebrain of 7.5-day old chick embryos using Rana temporaria early gastrula ectoderm as reacting tissue (Mikhailov and Gorgolyuk, Soviet Scientific Reviews, Section of Physiology and General Biology, Vol. 1: 267-306, 1987). The corresponding protease-sensitive agent was extracted, partially purified by chromatography on DEAE-Toyopearl and Heparin-Ultragel columns, and its neuralizing activity was tested in vitro on ectoderm isolated from early gastrulae of R. temporaria, Triturus alpestris, and Xenopus laevis at different concentrations and for different periods of time (animal cap assay). Induction of neural structures was found in R. temporaria and T. alpestris explants (up to 100 and 60%, respectively), but not in cultures of X. laevis ectoderm. Under our experimental conditions, so-called "autoneuralization" of the ectoderm explants can safely be excluded. The results are discussed in relation to the neural competence of amphibian ectoderm and the mechanisms of neuralizing actions of different factors which might be involved in neural induction and patterning.

Animals↗
PubMed1989

Gangliosides of sea urchin embryos. Their localization and participation in early development.

The influence of antibodies to gangliosides of sea urchin Strongylocentrotus intermedius eggs on early embryos of this species was studied. gamma-Globulins were isolated from rabbit anti-ganglioside serum by micropreparative electrophoresis. These gamma-globulins produced anomalies in the development of embryos permeabilized in Triton X-100. The anomalies were not observed when anti-ganglioside gamma-globulins were added to the incubation medium together with gangliosides or when the permeabilized embryos were incubated with gamma-globulins of normal rabbit serum. Pretreatment of S. intermedius embryos with serotonin, tryptamine or some other indole derivatives led to the disappearance of ganglioside determinants from the cell surface and sharply increased immunofluorescence within the cell. Such pretreatment of embryos increased the amount of cell-associated gangliosides more than threefold as compared to untreated embryos. Serotonin was shown to bind specifically to sea urchin gangliosides immobilized on octyl-Sepharose. These observations suggest that cell-surface gangliosides, after binding drugs, are internalized and that serotonin and its antagonists inhibit the transport of newly synthesized gangliosides to the cell-surface membrane.

Animals↗
PubMed1988

Concanavalin A induces neural tissue and cartilage in amphibian early gastrula ectoderm.

We have studied in vitro differentiation of explants of the amphibian (Rana temporaria) early gastrula ectoderm after treatment with various concentrations (50-300 micrograms/ml) of 'free' and Sepharose-bound concanavalin A (Con A). The explants were incubated with Con A for 3 h at 20 degrees C; the rolling up of the explants was prevented by using special weights. We have demonstrated that: (1) free Con A has an inducing action on the explants in the concentration range 100-300 micrograms/ml medium; (2) when treated with Con A the explants produce neural tissue (50-70%), cartilage (20-40%) and, rarely, lentoids (5-10%); (3) the frequency of neural and cartilage inductions was similar at various Con A concentrations; (4) alpha-methyl-D-mannoside pyranoside inhibited the Con A effects; (5) Sepharose-bound Con A had no effect on the explants, although it was bound to the cell surface of the ectoderm inner layer. Possible mechanisms of the neutralizing and chondrogenic effects of Con A on ectodermal explants are discussed.

Animals↗
PubMed1982

Molecular cloning of double-stranded cDNA from the eye lens of the frog Rana temporaria: construction of the cDNA clonotheque and identification of a clone containing the nucleotide sequences of the lambda-crystallin gene.

Poly(A)+ RNA from the lens of the frog Rana temporaria contains three components (1200 +/- 50, 1000 +/- 50, and 900 +/- 50 bp in size) and a more heterogeneous RNA species with a length of 650-750 nucleotides. This RNA was used as a template for the AMV reverse transcriptase and Escherichia coli DNA-polymerase I and the total cDNA obtained was cloned in the PstI site of the pBR322 plasmid vector. Recombinant plasmids corresponding to abundant poly(A)+ RNA classes contain cDNA inserts from less than or equal to 200 to 1200 nucleotides in length. Part of the library (clonotheque) was divided into classes differing in the presence of absence of the restriction sites for BamHI, EcoRI and HindIII restriction endonucleases. The clones belonging to each of the five classes were characterized by the hybridization-translation test. The translation product of mRNA hybridizing with the clone pRT(1)294 has an M4 of about 22 000 and is specifically precipitated by the antiserum to lambda-crystallins of Rana temporaria. The size of the cDNA present in pRT(1)294, equal to 580 +/- 20 bp, is sufficient for coding the greater part of the lambda-crystallin amino acid sequence. On the basis of these data, we conclude that the clone pRT(1)294 codes for one of the frog lambda-crystallins.

Animals↗
PubMed1981

Immunochemical study of gangliosides at the cell surface of sea urchin embryos.

Two main gangliosides (G-1 and G-2) were isolated from eggs and embryos S. intermedius. They contain glucose, N-glucolylneuraminic acids, phytosphyngosine, fatty acids and alpha-hydroxy fatty acids. Molar ratios and sequence of these components are the same for both gangliosides, but G-2 contains sulphate residue which is attached to the terminal neuraminic acid. To obtain specific antisera rabbits were immunized by G-1 or G-2, which were mixed with bovine serum albumin and Freund's adjuvant. Both gangliosides possessed electrophoretic and antigenic heterogeneity. G-1 and G-2 gangliosides have common and individual antigenic determinants. Glucosylceramide of gangliosides is immunologically inactive. Individual antigenic specificity of the gangliosides depends on the presence of N-glycolylneuraminic acid (G-1) and SO3H-group (G-2). Egg gangliosides were demonstrated by immunofluorescence throughout the cell surface. After fertilization of immunofluorescent label was concentrated on one pole of the embryo only. During the development of specific fluorescence was again uniformly distributed at the blastomer surface. The most intense fluorescence was observed in the junction areas of the blastomers.

Animals↗
PubMed1981

Unusual gangliosides of eggs and embryos of the sea urchin Strongylocentrotus intermedius. Structure and density-dependence of surface localization.

From eggs and embryos of the sea urchin Strongylocentrotus intermedius two gangliosides, provisionally named G-1 and G-2, were isolated in the pure state. Both gangliosides contained glucose, N-glycoloylneuraminic acid and sphingosines in a 2:2:1 ratio; G-2 contained also a sulfate group, and yielded G-1 on desulfation. By periodate oxidation/borohydride reduction, permethylation analysis, neuraminidase degradation, analysis of the aldohexitol acetates and mass-spectrometry G-1 and G-2 were shown to have hitherto unknown structures: G-1 was identified as N-glycoloylneuraminosyl-(alpha 2 leads to 6)-glucosyl-(1 leads to 8)-N-glycoloylneuraminosyl-(2 leads to 6)-glucosyl-(1 leads to 1)-ceramide, and G-2 as sulfated G-1, carrying a sulfate ester group at C-8 of the terminal sialic acid. Antisera against the two gangliosides were prepared in rabbits by immunization with ganglioside G-1 or G-2. The specificity of the antisera was revealed by immunoelectrophoresis and immunodiffusion. The antisera did not react with bovine-brain and rat-liver gangliosides, with glucosylceramide and with various hydrolytic fragments of G-1 and G-2. The surface localization of the gangliosides in embryos incubated at different cell densities was studied by immunofluorescence microscopy. The intensity of the immunofluorescence was found to increase with decreasing cell density, indicating a different surface organization in sparse and dense embryos. In the sparse embryos immunofluorescence was seen mainly in the contact regions between the blastomers.

Animals↗