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Neural differentiation is specified for the first time during vertebrate's development in a part of cells of the embryonic ectoderm under the influence of signals emanating from neighboring tissues: the phenomenon of neural induction. As it was established more then 10 years ago by experiments with the Xenopus embryos, the inhibition of BMP signaling cascade in precocious of neural cells plays the main role in this phenomenon. As a result, the epidermal differentiation program is blocked in these cells, and instead the neural program appears to be activated in them on default. This so-called the default model of neural induction was also confirmed by experiments in other organisms. At the same time, an important role of FGF and Wnt signaling cascades in modulation of BMP cascade during neural induction was recently established. Identification and investigation of many novel proteins involved in the process of neural induction allows one to come back at the novel level, namely at the level of mathematical modeling, to one of the basic challenge of developmental biology: the problem of spatial patterning of cell differentiation during embryogenesis.

In the present work, principles of formation of germ line cells are reviewed. Germ line cells separate themselves from the rest of the embryo at the early stages of embryogenesis. In certain animal groups, formation of precursors of germ cells occurs by induction by surrounding cells. However, for most animal taxons, formation of primordial germ cells (PGCs) is determined by inheritance of certain maternal determinants--the so-called germ plasm. It is formed by mitochondria, electron-dense granules with the complex structure, and maternal RNAs and proteins necessary for formation of germ line. In Xenopus, the source of material for germ plasm is a mitochondrial cloud, which also specifically binds and transports to the vegetal pole maternal RNAs important for PGC formation. Cis elements determining the transport of these RNAs are usually located in the 3' untranslated region of RNA, and their function is mediated by binding of trans acting protein factors. In addition to a specific localization of certain macromolecules in germ plasm, special status of germ line cells is provided by degradation of RNA and protein components of germ plasm in somatic cells, silencing of transcription in PGCs until advanced stages of embryogenesis, and specific regulation of RNA translation in somatic and germ cells. In this review, we also briefly discuss results obtained by authors regarding the properties of a novel component of Xenopus germ plasm, namely maternal RNA germes, and encoded protein.

The review considers the advantages of Xenopus embryos as an experimental model to study the molecular-genetic mechanisms of embryo development. The results are described that were obtained with this model in studies on the early brain development within the framework of the Russian program Human Genome.

Acetylcholine (ACh) hyperpolarized the rat diaphragm muscle fibers by 4.5 +/- 0.8 mV (K0.5 = = 36 +/- 6 nmol/l). The AC-induced hyperpolarization was blocked by d-tubocurarine and ouabain in nanomolar concentrations. This effect of ACh was not observed in cultured C2C12 muscle cells and in Xenopus oocytes with expressed embryonic mouse muscle nicotinic acetylcholine receptors (nAChR) or with neuronal alpha 4 beta 2 nAChR. In membrane preparations from the Torpedo californica electric organ, containing both nAChR and Na, K-ATPase, 10 nmol/l ouabain modulated the binding kinetics of the cholinergic ligand dansyl-C6-choline to the nAChR. These results suggest that in-sensitive alpha 2 isoform) and nAChR in a state with high affinity to Ach and d-tubocurarine may form a functional complex in which binding of ACh to nAchR is coupled to activation of the Na, K-ATPase.

The recombinant mouse brain serotonin receptor (5HT1c) was used to study the response of plant cells and oocytes to a stress signal activated by the serotonin-serotonin receptor interaction and associated Ca2+ flow. Based on plant expression vectors, recombinant constructs were obtained to direct production of 5HT1c fused with the green fluorescent protein in plant cells. The mRNAs for hybrid proteins were synthesized in an in vitro transcription system. The expression and function of the hybrid protein and the function of the associated ion channels were electrophysiologically studied in Xenopus laevis oocytes injected with the hybrid mRNA. The hybrid protein was functional and changed the operation of the Ca2+ channel in oocytes. To study the expression of the hybrid constructs in plant cells, the in vitro transcription product was inoculated in tobacco leaves, which then fluoresced.

Xenon (Xe) is being more widely used in medicine owing to its unique physical-and-chemical properties of a noble gas. However, the knowledge about the physiological and patho-physiological changes occurring in the organism and in its separate structures during the interaction with Xe is still scanty. The aim of this survey was to briefly describe the presently known Xe biological-and-medical properties and certain mechanisms of Xe impact produced on cells and receptors as well as on the release of mediators and hormones. Besides, the Xe hemodynamic effects are also defined. The conclusion is that the Xe effect can be of a complex nature and can depend on the conditions of the body vital activity (optimal condition, activation, lesion), which predetermine, in their turn, the performance of the structural-and-functional units of various cellular systems.

In the present work we describe the construction of expression system for inducible murine macrophage nitric oxide synthase (iNOS) in E.coli. For this purpose a framework of translation iNOS was cloned in the expression vector pCWori +. As biosynthesis of active iNOS requires coexpression of calmodulin (CaM), for obtaining functional expression of this protein we conducted amplification of an appropriate site of the library total cDNA a frog Xenopus laevis, then plasmids for coexpression of calmodulin were constructed under a control tac and T7 promotors. Recombinant iNOS was functionally active as revealed by the analysis of CO-reduced spectrums, detection of derivation NO with the help of reaction conversion HbO2 in metHb, and also identification of a molecule NO by EPR method. The output of recombinant iNOS at usage of different constructions varied from 10 up to 22 mg/l culture, and specific activity was from 0.42 up to 0.64 U/mg of protein. These data coincide with the earlier published results of other investigators. It was established, that the expressed iNOS is associated to a membrane fraction of cells, thus in the 105,000 g-supernatant the activity of an enzyme is not detected. The data on membrane localization iNOS are inconsistent with general notion this enzyme is soluble.

The RNA-binding proteins from amphibian (Rana temporaria and Xenopus laevis) oocytes contain a cAMP-independent caseintype protein kinase activity. This enzyme can phosphorylate casein but does not phosphorylate histones. Using high voltage paper electrophoresis of acid hydrolysate of [32P]casein, it was found that P-O-phosphoserine and [32P]-O-phosphothreonine are formed via the phosphorylation reaction. Protein kinase retains the ability to bind poly(U) under physiological ionic strength values. It was shown that RNA-binding proteins do not contain any detectable forms of phosphatase or protease which might distort the results of phosphorylation of endogenous and exogenous substrates.

RNA-binding proteins isolated from amphibian oocytes ribosome-free extract by affinity chromatography on poly (U)-Sepharose possess an endogenous protein kinase activity. Incubation of these proteins with [gamma-32P] ATP leads to the incorporation of labelled phosphate into 6-7 polypeptide chains with molecular masses from 20 000 to 80 000, which are estimated by disk-electrophoresis in the presence of sodium dodecyl sulphate, followed by autoradiography of dried gels. High-voltage paper electrophoresis of acid hydrolysates of labelled proteins showed that mainly [32P]phosphoserine is formed in this reaction. Phosphorylation is not stimulated by cAMP and reaches its maximum by 20 degrees and pH near 8. The presence of poly(U) in the reactional mixture inhibits phosphorylation considerably. The opportunity of partial decrease or loss of RNA-binding activity due to phosphorylation of RNA-binding proteins is discussed.

As the investigation performed demonstrated, there is no principle differences in cytological organization in kidneys of five species of Amphibia whose mode of life to a certain extent is connected with water environment. Nevertheless, in different species epithelium of proximal parts of nephrons demonstrates various intensity of apocrinic secretion. Granules situating in the supranuclear zone of the epithelial cells of these parts are, in fact, autophagic lysosomes, their function is evidently connected with both lysis of the absorbed proteins and with autolysis of the apical cellular part in the process of secretion. The epithelial cytoplasm in the distal part of the nephron is characterized by a high succinate dehydrogenase activity; it is connected with its main function--osmoregulation. There are dark and light cells, resembling those in higher vertebrates, in the connecting part and in the collecting tubes. Ultrastructural organization of the brown frog nephron cells has much in common with that of epithelium of the secondary kidney urinary canaliculi.

To describe the kinetics of potassium permeability (conductance) changes in the squid giant axon membrane the Hodgkin--Huxley formulation uses a single first-order in time variable n with forward and backward rate constants, respectively alpha-n and beta-n, potential-dependent but time-independent. It has been shown by Frankenhaeuser that in the potassium-carrying system of the myelinated nerve fiber membrane of Xenopus laevis the rate constant beta-n is dependent on the duration of previous depolarization, i. e. the beta-n of this membrane is time-dependent. Started from the FitzHugh--Cole--Moore translation principle for potassium current experimental data of Frankenhaeuser have been analysed to show that the rate constant alpha-n in the X. laevis nerve fiber membrane is also time-dependent. To keep the conventional Hodgkin--Huxley formulation valid in case of the potassium-carrying system of the X. laevis nodal membrane involvement of an additional first--order in time component (n-II) has been postulated, which is compatible with Frankenhaeuser's experimental results. This component n-II appears to be identical to the n-II-component in the potassium-carrying system of the Rana ridibunda nerve fiber membrane. Both are rather slow and activated within the potential range more negative than the basic n-I-component (corresponding to Frankenhaeuser's variable n). The component n-I seems to be identical to the n-component of many other excitable membranes with fast action potentials. The existence of the third, very slow nIII-component is also possible. The independent components in question are believed to be associated with different independent potassium channels within the same membrane. It is likely that the existence of several independent components is a general feature of the potassium-carrying mechanism in the excitable membranes essential for a particular type of electrogenesis.

The cytoplasm of the egg vegetal hemisphere plays the determining role in the isolation and differentiation of germ cells. Cytoplasmic factors of unknown nature prevent certanin blastomeres from somatic differentiation. In the developing germ cells, a large amount of material (in which acid proteins are a constant component) passes from the nucleus to the cytoplasm. This fine fibrous material may take the form of nucleolus-like bodies or dense granules (polar granules in the insect eggs, dense bodies in the amphibian germ plasm, intermitochondrial cement in oocytes of various animals, chromatoid body in spermatocytes). The application of the term "determinants of germ cells" for designation of these structure, as it takes in the electron microscopy literature, appears to be incorrect. Their appearance is a consequence of the determining influence of cytoplasmic factors, rather than their cause. In lower invertebrates, the germ cells may arise in adult specimens due to the embryonic reserve of totipotent elements (neoblasts or interstitial cells). The transformation of these cells in the germ ones is accompanied by the release of a great amount of fine fibrous material from the nucleus to the cytoplasm as well. The problem of determinants of germ cells is considered with respect to the problem of ooplasmic segregation.

After the injury of the thalamus right hemisphere in tadpoles and young frogs X. laevis, 3H-thymidine incorporated in the cells of the thalamus ventricular zone, but not in the middle and large neurons of the type of neurons of the trigeminal nerve mesencephalic nucleus and the large ganglion cells of VI and VIII layers of the thalamus cortex. The brain trauma in tadpoles resulted in the activation of cell proliferation in the ventricular zone, whereas in young frogs the proliferation of glyocytes was activated. The relation of the proliferative reaction of certain types of brain cells to the trauma to the loss of ability for brain regeneration is discussed.

Localization of specific proteins at preliminary stained with azan and embedded in balsam sections of amphibian eye lens (Rana temporaria, Xenopus laevis) was studied by indirect immunofluorescence. The analysis was performed on the lens of intact animals as well as on lens induced in amphibia gastrula ectoderm in vitro. To remove balsam the lens sections were successively washed by xylene, ethanol and saline (pH 7.1). Then they were treated according to the general principles of immunohistochemical analysis. Specific antigens have been thus shown to be detectable at lens sections which had been kept in balsam for over a year. The immunofluorescent reaction to lens proteins was negative at more prolonged storage of the sections (2--3 years).

There was studied the effect of cycloheximide on the changes in the X. laevis and A. stellatus oocytes maturing under the influence of active cytoplasm, taken from the maturing oocytes, and, in the control series, under the influence of progesterone. The suppression of protein synthesis in the X. laevis oocytes by means of cycloheximide by 90--95% did not prevent the amplification of the factor of disintegration of the germinal vesicle membrane after 4 and 5 transfers of the active cytoplasm through the cycloheximide-treated oocytes; no pseudogastrulation was observed in such oocytes. Under the similar suppression of protein synthesis in the A. stellatus oocytes, the germinal vesicle did not break down already after the first injection of active cytoplasm; such oocytes acquried, however, the ability of cortical reaction. The cycloheximide-treated oocytes of both the species did not mature under the effect of progesterone. The fully grown A. stellatus oocytes matured after the injection of active cytoplasm from the mature X. laevis oocytes.

The intracellular injection of cytoplasm from the maturing oocytes of X. laevis and A. stellatus in oocytes of the same species which did not complete the vitellogenesis and are not able to mature under the effect of progesterone resulted in the disintegration of the germinal vesicle membrane in the oocytes of all sizes under study. In X. laevis the ability to mature under the effect of progesterone appears in the oocytes with the diameter over 1.1 mm. Cycloheximide inhibits the germinal vesicle membrane disintegration in the X. laevis oocytes, but not in those of A. stellatus. Cycloheximide inhibits the pseudogastrulation which was observed in the X. laevis oocytes with the diameter from 0.8 to 1.4 mm.

Some present-day conceptions on the structure and physiochemical and functional properties of mitochondrial ribosomes of higher and lower eukaryotes are reviewed. Mitochondrial ribosomes are compared to the ribosomes of prokaryotic and eukaryotic types and plastid ribosomes; biogenesis and functions of mitochondrial ribosomes are also discussed.

The suspension of mitochondria isolated from the loach embryos or the frog heart were injected in the oocytes or fertilized eggs of the loach, newt, toad and frog in the amount roughly equivalent to the content of mitochondria in the egg. After the injection the oocytes did not differ during several days from the normal ones and the fertilized eggs of the loach, newt and South Afican clawed toad developed normally. The activity of cytochrome oxidase in the injected oocytes was kept at a somewhat higher level (1.4 to 1.9 vs 1.0 in the control) during several days. In the developing eggs the activity of cytochrome oxidase began to decrease from the blastula stage and attained rapidly the control level. The decrease of the enzyme activity is due to non-specific degradation of excessive mitochondria or to compensatory inactivation of the enzyme ensuring the maintenance of its normal activity during the development.

When cultivating the nervous tissue of newborn rats, rabbit embryos and tadpoles (as whole fragments or dissociated cells), 3 groups of neuroblasts are distinguished: differentiating, migrating and with growing processes. These groups correspond to different stages of neuroblast development in vivo and their presence in the tissue cultures of different brain regions reflects the heterochrony of cell development in these regions. The neuroblasts realize their morphogenetic potential within several days of cultivation irrespective of the contact with the other cells but the subsequent differentiation (dendrite branching, nuclear clearance etc.) proceeds only in cells united in aggregates.