[Changes of the genome-wide DNA methylation level in various regions of the rat brain with incomplete cerebral ischemia]

OBJECTIVE

To quantify genome-wide DNA methylation in the olfactory bulbs, fronto-parietal and occipital regions, and cerebellum in normal male Wistar rats and in modeling incomplete cerebral ischemia caused by permanent bilateral occlusion of the common carotid arteries.

MATERIAL AND METHODS

The study was performed on 23 male Wistar rats divided into groups: «Sham operation» and «Cerebral ischemia». The level of genome-wide methylation of CCGG sites was determined by methyl-sensitive restriction using MspI/HpaII endonucleases followed by densitometric analysis of electrophoregrams by ImageJ software.

RESULTS

Incomplete cerebral ischemia on the 7th day leads to 56.3% (95% CI: 33.2-76.90) mortality. In the surviving rats of the «Cerebral ischemia» group, compared with the animals of the «Sham operation» group, a pronounced neurological deficit was observed, which was accompanied by changes in the level of whole-genome DNA methylation in the nervous tissue of brain structures (p<0.05). Incomplete cerebral ischemia in male Wistar rats was characterized by interhemispheric asymmetry in the severity and direction of the epigenomic reaction of the nervous tissue in both ischemic and non-ischemic areas of the brain.

CONCLUSION

It is likely that it is precisely this dynamics of changes in the status of genome-wide DNA methylation in the nervous tissue that imparts plasticity to neuronal function during ischemic damage.

The possible effect of lactoferrin on the epigenetic characteristics of early mammalian embryos exposed to bisphenol A

BACKGROUND

The main objective of this review was to state a hypothetical mechanism of the antitoxic effect of lactoferrin (Lf) on embryos exposed to bisphenol A (BPA). On this basis, it is possible to suggest Lf as a potential protective health component before conception upon toxic effects and viral infections.

METHODS

The narrative review was performed using systematic review methods to identify relevant literature. The resources required for this study were obtained by searching the electronic database PubMed (MEDLINE). Articles were searched using the keywords "BPA," "lactoferrin," "DNA-methylation," "epigenetic," "mammals," "human," and "mouse." The inclusion criteria were as follows: (a) primary or original research; (b) study of epigenetic modification; and (c) study focuses on early mammalian development.

RESULTS

Presented data demonstrate that Lf can modulate epigenetical characteristic, such as DNA methylation and reactive oxygen species (ROS), and, thereby, may serve as a potential readily available pharmaceutical product.

CONCLUSION

Suggested hypothesis is based on the important interrelated role of changes in epigenetic modifications and oxidative stress in early embryogenesis under the influence of BPA and virus infection as a cause of the development of pathologies in the adult organism.

Length Polymorphism and Methylation Status of UPS29 Minisatellite of the ACAP3 Gene as Molecular Biomarker of Epilepsy. Sex Differences in Seizure Types and Symptoms

Epilepsy is a neurological disease with different clinical forms and inter-individuals heterogeneity, which may be associated with genetic and/or epigenetic polymorphisms of tandem-repeated noncoding DNA. These polymorphisms may serve as predictive biomarkers of various forms of epilepsy. ACAP3 is the protein regulating morphogenesis of neurons and neuronal migration and is an integral component of important signaling pathways. This study aimed to carry out an association analysis of the length polymorphism and DNA methylation of the UPS29 minisatellite of the ACAP3 gene in patients with epilepsy. We revealed an association of short UPS29 alleles with increased risk of development of symptomatic and cryptogenic epilepsy in women, and also with cerebrovascular pathologies, structural changes in the brain, neurological status, and the clinical pattern of seizures in both women and men. The increase of frequency of hypomethylated UPS29 alleles in men with symptomatic epilepsy, and in women with both symptomatic and cryptogenic epilepsy was observed. For patients with hypomethylated UPS29 alleles, we also observed structural changes in the brain, neurological status, and the clinical pattern of seizures. These associations had sex-specific nature similar to a genetic association. In contrast with length polymorphism epigenetic changes affected predominantly the long UPS29 allele. We suppose that genetic and epigenetic alterations UPS29 can modify ACAP3 expression and thereby affect the development and clinical course of epilepsy.

[THE INFLUENCE OF THE PREPARATION PRETREATMENT ON IN SITU DETECTION OF 5-METHYLCYTOSINE IN METAPHASE CHROMOSOMES AND IN INTERPHASE NUCLEI]

Qualitative and quantitate analysis of DNA methylation in situ at the level of cells, chromosomes and chromosomal domains is extremely important for the diagnosis and treatment of various diseases, the study of ageing and the consequences of environmental impacts. An important question arises, whether the revealed in situ methylation pattern reflects DNA methylation per se and (or) availability of the DNA for antibodies, which in turn depends on the peculiarities of chromatin structure and chromosome condensation. These events can lead to an incorrect evaluation of the actual pattern of DNA methylation. To avoid this shortcoming as far as possible, we have modified the most widely used method of revealing 5-methylcytosine in situ with monoclonal antibodies. Here we have shown that the detection of DNA methylation staining of chromosomes including C-heterochromatin, chromosomal arms and sister chromatids is drastically dependent on pretreatment of chromosomal preparations for immunocytochemical study using fluorescent antibodies. Using undifferentiated stem cells of mouse embryonal carcinoma line F9, it has been found that change in preparations storage results in a sharp fluorescence decrease up to complete disappearance of the signal in centromeric heterochromatin. With the help of the method described in the work, we have first revealed the asymmetry of sister chromatids methylation in metaphase chromosomes of F9 cell and lymphocytes of human periphery blood. This may lead to asymmetry of transcriptional signature of daughter cells after division. The proposed here modification of 5-methylcytosine detection in situ provides a more complete characterization of methylation of chromosomes and chromosomal domains, compared to previously published methods.

[[Length polymorphism of minisatellite repeat B2-VNTR of the bradykinin B2 receptor gene in healthy Russians and in patients with coronary heart disease]

Bradykinin B2 receptor is involved in many processes, including the regulation of blood pressure and smooth muscle contraction, vasodilation, inflammation, edema, cell proliferation, pain. It is suggested that this receptor may be one of the factors that have cardioprotective and infarct-limiting effects. It is assumed that certain genetic variants in both coding and non-coding regions ofBDKRB2 gene may influence its expression. In the 3'-untranslated region of BDKRB2 exon 3 the minisatellite repeat B2-VNTR is located. B2-VNTR has previously been shown to affect the BDKRB2 mRNA stability. Therefore, it is important to perform the molecular genetic analysis of this minisatellite in patients with different forms of coronary heart disease in order to reveal possible associations between specific B2-VNTR alleles and certain clinical forms of coronary heart disease. In the present study, a comparative analysis of the allele and genotype frequencies of B2-VNTR was carried out in groups of healthy individuals and patients with two clinical forms of coronary heart disease (angina pectoris and myocardial infarction), ethnically Russian. The results of the B2-VNTR length polymorphism analysis indicate that this tandem repeat may be attributed to a class of low polymorphic and non-hypervariable minisatellite. In all analyzed groups we revealed three B2-VNTR alleles, consisting of 43, 38 and 33 repeat units. Alleles of 43 and 33 repeats were major in all investigated groups. No statistically significant differences were found in the B2-VNTR allele and genotype frequencies between men and women in control group, and also between healthy men and men with angina pectoris and myocardial infarction. Thus, B2-VNTR length polymorphism was not associated with these clinical forms of coronary heart disease in Russian men. However, we do not exclude the possibility of association between the B2-VNTR short alleles (38 and 33 repeats) and cardioprotective effects of bradykinin B2 receptor in women with coronary heart disease. This hypothesis requires further investigation.

[Human intra-intronic minisatellite UPS29 associated with neurological diseases regulates reporter gene EGFP expression depending on cell type]

Earlier, it was established that polymorphism of minisatellite UPS29 located in one of introns of human gene CENTB5 (ACAP3) was associated with Parkinson's disease and epilepsy. The main aim of this work was to elucidate if that minisatellite could regulate reporter gene activity, and if such activity was tissue (cell)-specific. To this end there was used transient transfection of HeLa cells, mouse embryonal carcinoma line F9, and rat astrocytes cultures with plasmides which contained reporter gene EGFP under eukaryotic promoter ROSA26 and different allelles of minisatellite UPS29. It was found that UPS29 possessed enhancer-like activity in neuronal type cells.

[CENTB5 gene expression in human and mouse]

Centaurin beta5 with unclear function belongs to protein family of centaurins. Human centaurin beta5 is encoded by gene CENTB5 whose intron 14-15 contains low variable minisatellite UPS29, and mouse homolog CENTB5 in analogous intron contains imperfect microsatellite repeat (CATG)19. Earlier we found the association between an occurrence of short UPS29 alleles with some forms of Parkinson disease and epilepsy. Besides this, both human and mice CENTB5 are localized in the same synteny group with SCNN1D and ACOT7 genes which are known to be expressed predominantly in nervous system. Mutations in these genes are connected with neurodegenerative processes and epilepsy. It is known that intra-intronic sequences can modulate genes of their location and neighbor and even remote genes. Using RT-PCR we carried out simultaneous analysis of CENTB5, SCNN1D and ACOT7 genes expression. Potential possibility of human intra-intronic tandem repeat UPS29 and of mouse intra-intronic tandem repeat (CATG)19 to regulate/modulate CENTB5, SCNN1D and ACOT7 activity was evaluated in silico. It was found that all these genes were expressed in all studied organs and tissues. It is suggested that minisatellite locus UPS29 can regulate an activity of CENTB5, SCNN1D and ACOT7 in nervous system cells.

Genetically altered animal models for Mas and angiotensin-(1-7)

Mas is the receptor for angiotensin-(1-7) and is involved in cardiovascular and neuronal regulation, in which the heptapeptide also plays a major role. Mas-deficient mice have been generated by us, and their characterization has shown that Mas has important functions in behaviour and cardiovascular regulation. These mice exhibit increased anxiety but, despite an enhanced long-term potentiation in the hippocampus, do not perform better in learning experiments. When Mas-deficient mice are backcrossed to the FVB/N genetic background, a cardiovascular phenotype is uncovered, in that the backcrossed animals become hypertensive. Concordant with our detection by fluorescent in situ hybridization of Mas mRNA in mouse endothelium, this phenotype is caused by endothelial dysfunction based on a dysbalance between nitric oxide and reactive oxygen species in the vessel wall. In agreement with these data, transgenic spontaneously hypertensive stroke-prone rats overexpressing ACE2 in the vessel wall exhibit reduced blood pressure as a result of improved endothelial function. Moreover, angiotensin-(1-7) overexpression in transgenic rats has cardioprotective and haemodynamic effects. In conclusion, the angiotensin-(1-7)-Mas axis has important functional implications for vascular regulation and blood pressure control, particularly in pathophysiological situations.

[Transgenerational transmission of bovine satellite DNA in transgenic mice]

Genetical, cytogenetical and molecular analysis was made for 5 generations of mice transgenic for bovine satellite DNA (Sat). In all cases transgenic mice were generated by crosses of transgenic males and females with normal (CBA x C57B1) mice. No abnormalities in the founder development were noticed. A normal (near 50 %) ratio of transgenic and nontransgenic offsprings was observed in blastocysts. However, profound differences occurred in the rate of transgene bearing offsprings, depending on the sex of grandparents rather than of parents. The grandfather Sat transmission resulted in the appearance of 0-52.4 % transgenic grandchildren, whereas the grandmother transmission ended in the theoretically expected rate. This means that stabilization of transsatellite took place upon the female germ line transmission (a positive grandmother effect). It is essential that in hemizygous transsatellite mice Sat integration led to the occurrence of mammary tumors, inflammation of uterine horns, and infringement of mother care of transgenic females. Simultaneous FISH and G-banding showed Sat to be localized in the internal region of chromosome 12 near Pax 9 and Brms 11 genes. Commonly, these genes are implicated in tumorigenesis as their expression decreases. Thus, a kind of silencing effect of these genes' expression may be supposed.

[Regulatory mechanisms of mammalian imprinting]

Epigenetic modifications, such as monoallelic DNA methylation, covalent histone modifications, nonhistone proteins, chromatin folding, heterochromatinization, spatial nucleus organization are reviewed with regard to establishment and maintenance of imprinting in mammals. Special attention is paid to repeated DNA sequences as intermediates of the above epigenetic modifications. A suggestion is put forward relative to importance of preimplantation development, in particular, to chromosome organization and segregation in the establishment of imprinting. Some futher directions of imprinting mechanisms are also discussed.

[Instability of repetitive units of foreign centromeric satellite DNA in transgenic mice and transfected cells]

Cytologically detectable instability of centromeric satellite DNA may cause hereditary disorders in human. To study the mechanisms of such instability, two transgenic mouse lines and 11 clones of transfected F9 mouse embryonic teratocarcinoma cells were obtained with the 3.8-kb repetitive unit (Sat) of Bos taurus satellite DNA IV. Intergeneration and somatic instability of exogenous satellite DNA (satDNA) was observed in transgenic mice and transfected cells as a change in nucleotide sequence of an internal Sat region approximately 1000 bp in size. Since Sat was in the hemizygous state in both cases by the experimental protocol, the instability was attributed to intra-allelic processes. Intergeneration instability probably took place in the premeiotic period of gametogenesis or in early embryo development and led to prenatal death of transgenic embryos after at least one generation. No direct or inverse correlation was observed between methylation and instability of Sat. The results testify that submicroscopic changes in highly repetitive noncoding DNA sequences may already affect the genome function in higher eukaryotes.

Bovine satellite DNA induces heterochromatinization of host chromosomal DNA in cells of trassatellite mouse embryonal carcinoma

Embryonal teratocarcinoma F9 cells were transfected with a fragment (3.8 kb) of bovine satellite DNA IV (Sat), which is not homologous to mouse satellite DNA. FISH analysis revealed various chromosomal integration sites of integrated Sat in different transsatellite clones. After several passages, transsatellite had a tendency to spread along chromosome bearing Sat in one of the studied lines. The integrated transsatellites were enriched with prolonged single-strand DNA regions (SSR) revealed by FISH without previous chromosomal denaturation, and were unmethylated. The observed SSR are presumably supposed to represent intermediates of transsatellite DNA instability via unequal sister chromatid exchanges. DAPI staining demonstrated that the integrated Sat induced the formation of prominent ectopic neoheterochromatin blocks in regions adjacent to integrated Sat. These blocks were located exclusively between integrated Sat and centromeric heterochromatin. Thus, mouse repetitive centromeric DNA (AT-rich, DAPI-positive) "spreads" along the chromosome in response to integration of the bovine satellite GC-rich DNA. The results obtained are discussed in the context of possible position effect variegation mechanisms operating in undifferentiated cells.

Epigenetic mechanisms for primary differentiation in mammalian embryos

This review examines main developments related to the interface between primary mammalian cell differentiation and various aspects of chromosomal structure changes, such as heterochromatin dynamics, DNA methylation, mitotic recombination, and inter- and intrachromosomal differentiation. In particular, X chromosome difference, imprinting, chromosomal banding, methylation pattern, single-strand DNA breaks, sister chromatid exchanges (SCEs), and sister chromatid asymmetry are considered. A hypothesis is put forward which implies the existence of an epigenetic asymmetry versus mirror symmetry of sister chromatids for any DNA sequences. Such epigenetic asymmetry appears as a result of asymmetry of sister chromatid organization and of SCE and is a necessary (not sufficient) condition for creating cell diversity. The sister chromatid asymmetry arises as a result of consecutive rounds of active and passive demethylation which leads after chromatin assembly events to chromatid difference. Single-strand DNA breaks that emerge during demethylation trigger reparation machinery, provend as sister chromatid exchanges, which are not epigenetically neutral in this case. Taken together, chromatid asymmetry and SCE lead to cell diversity regarding their future fate. Such cells are considered pluripotent stem cells which after interplay between a set of chromosomal domains and certain substances localized within the cytoplasmic compartments (and possibly cell interactions) can cause sister cells to express different gene chains. A model is suggested that may be useful for stem cell technology and studies of carcinogenesis.

[Single-strand DNA breaks in brain cells of different rat strains under normal condition and during exposure to stress]

This study was aimed to characterize pattern of occurrence of spontaneous single-strand breaks in situ in glial and neuronal nuclei of the cortex, middle brain and hyppocapmi (CA3 field) of rats selected for a threshold of nervous system excitability, and to study the influence of stress of various modality on such breaks. The results obtained evidence that: 1) intact animals possess a subpopulation of glial and neuronal cells revealed following gap filling in situ in opposite to other types of terminally differentiated non-proliferating cells; 2) the size of such a subpopulation differs depending on the lines of examined rats, parts of brain, and the type of stress.

[Satellite DNA and disease--possible mechanisms. Minisatellite instability]

The main possible molecular mechanisms of minisatellite DNA instability are reviewed and compared with those of the trinucleotide repeat instability. Evidence indicating that some human diseases are associated with minisatellite DNA instability is presented including data on minisatellite DNA expansion.

[Modeling heterochromatin regions in transgenic mice]

Transgenic mice carrying bovine satellite DNA IV were obtained. The size of the transgene integrated into the mouse genome was approximately 390 kb (about 100 transgene copies) as determined by a semiquantitative PCR. Restriction analysis with isoschizomeric restrictases HpaII and MspI, showed that the alien DNA was methylated. In the genome of a transgenic founder male, two integration sites for satellite DNA IV were revealed by in situ hybridization and in situ PCR. These sites are situated on two different chromosomes: in pericentromeric heterochromatin and within a chromosomal arm. In transgenic mice, de novo formation of heterochromatin regions (C-block and the CMA3 disk within the centromeric heterochromatin of another chromosome) was revealed by C-banding and staining with chromomycin A3. This formation is not characteristic of mice, because their chromosomes normally contain no interstitial C-blocks or sequences intensely stained by chromomycin A3.

[Satellite DNA and disease--possible mechanisms. Trinucleotide repeats]

The new data on the mechanisms underlying trinucleotide repeat expansion are reviewed with special reference to the role of chromatin structure, DNA replication, methylation, and amplification in repeat expansion during ontogeny. A hypothesis is advanced as to the crucial role of processes that occur at the preimplantation developmental stage, such as sister chromatid exchanges, single-strand DNA breaks, and demethylation. The molecular and cellular events responsible for association between trinucleotide expansion and various diseases are discussed.

[Noninduced single-stranded breaks in DNA in murine F9 teratocarcinoma cells]

Our previous study demonstrated the high incidence of non-induced DNA single strand breaks (SSB) in preimplantation mouse embryo genom (Patkin et al., 1994). F9 mouse teratocarcinoma cell line is an in vitro model for early embryonal differentiation, since F9 cells remind in many respects the inner cell mass cells of mouse blastocyst and are capable of differentiation under retinoic acid (RA) and dibutyryl cAMP (db-cAMP) treatment. Using gap filling reaction of F9 metaphase chromosomes and single-cell DNA electrophoresis, we have observed multiple SSB in undifferentiated F9 cells as well as in F9 cells at the early steps of RA-induced differentiation (days of RA treatment), but not in terminally differentiated F9 cells and in mouse embryonal fibroblasts. Rad51 nuclear protein that binds specifically single stranded DNA is highly expressed in all cells of undifferentiated F9 population and is not expressed in terminally differentiated F9 population. Multiple SSB could lead to enhanced rate of sister chromatid exchanges (SCE) in F9 cells. In undifferentiated F9 population the level of SCE was 9.6 +/- 0.44 per metaphase, that was not higher than in NIH 3T3 cell line. However, RA treatment for 48 h led to rising the SCE level up to 16.68 +/- 0.72 followed by its decrease to the initial rate by 72 h of RA treatment. Since the enhanced level of SSB in undifferentiated F9 cells and in mouse blastocyst does not normally lead to chromosomal instability, we consider SSB to be a natural consequence of fast-going DNA replication in these cells.

[The detection of transgenic animals using a polymerase chain reaction in situ]

The technique for detecting both foreign and host specific DNA sequences inside nuclei and chromosomes of single cells of transgenic mice with the help of polymerase chain reaction (PCR) in situ is described. The mouse preimplantation and postimplantation embryonic and adult cells were studied. The methodology is described in detail with particular attention to the optimization of composition of reaction mixture, kind of fixation and preliminary denaturation of target DNA. The reaction takes only several hours and needs no sophisticated equipment.

Persistence of human mitochondrial DNA throughout the development to the blastocyst of mouse zygotes microinjected with human mitochondria

The conditions for transfer of human mitochondria into fertilised mouse ova were elaborated. Species-specific primers were designed to discriminate human mitochondrial DNA (mtDNA) and the endogenous mtDNA in the preimplantation embryos. Human mitochondria isolated from the HepG2 cell line were microinjected into murine zygotes, and the latter cultured for 96 h to the blastocyst stage. The polymerase chain reaction allowed the detection of human mtDNA at every stage of embryo cleavage. In some cases a clear disparity in distribution of human mtDNA among blastomeres was evident.

The influence of demethylating agents on preimplantation development of mice

The effects of two demethylating drugs with a different mechanism of action (5-azacytidine (Aza) and L-ethionine (Eth)) on mouse preimplantation development were investigated. Preimplantation embryos were cultured for 24 h in the presence of the drug and for an additional 24 or 48 h (depending on the cleavage stage) in medium supplemented with bromodeoxyuridine to reveal sister chromatid exchanges (SCEs) and the number of cell cycles performed before harvesting. Striking differences between the two drugs were observed in their influence on proliferation of blastomeres, primary differentiation and sister chromatid differentiation (SCD), and in the pattern of DNA methylation and the frequency of SCEs per cell. At a final concentration of 1 microM Aza had no effects, whereas higher concentrations stopped development of all stages except the zygote. In contrast Eth treatments (5 mM) resulted in a severe reduction of the mean cell number per embryo in comparison with controls. Moreover both the absence of blastocyst formation and no effects on mitotic activity were detected. The most prominent effect of Eth was detected at the zygote and 4-cell stages. An unexpected decrease in SCE frequency in Eth-treated morulae and 4-cell embryos has been observed. Data are explained taking into account the different mechanisms of action of the agents.

DNA-strand breaks in chromosomes of early mouse embryos as detected by in situ nick translation and gap filling

The nick translation and gap filling procedures, without external addition of nicking enzymes, were performed in situ on fixed chromosomes of mouse preimplantation and postimplantation embryos and of bone marrow in order to detect possible DNA single-strand breaks (nicks and (or) gaps). All chromosome preparations were made using the same technique. Nick translation of chromosomal DNA with DNA polymerase I (Pol I) or gap filling with the Klenow fragment of Pol I in the presence of biotinylated-dUTP, demonstrated a regular absence of label on chromosomes of postimplantation embryos and bone marrow. No difference in sensitivity was found between the holoenzyme and the Klenow fragment. In preimplantation embryos, the chromosome reactivity in nick translation was highest at the blastocyst stage and varied according to cleavage divisions of the zygote.

Single-strand DNA breaks in nuclei of early mouse embryos detected by in situ nick translation

The nick translation procedure without external addition of nicking enzymes was performed in situ on fixed nuclei of mouse preimplantation, and postimplantation embryos, as well as bone marrow in order to detect possible DNA single-strand breaks. All preparations of nuclei were made using the same technique. Nick translation of nuclear DNA with DNA polymerase I in the presence of biotinylated-dUTP demonstrated a characteristic absence of label on nuclei of postimplantation embryos and bone marrow. The nuclear reactivity varied according to the cleavage divisions of the zygote, being highest at the four-cell stage.

Spontaneous sister chromatid differentiation (SCD) and sister chromatid exchange (SCE) in mouse blastocyst chromosomes

The phenomenon of spontaneous differentiation (without bromodeoxyuridine in the culture medium) of sister chromatids of mouse chromosomes at the blastocyst stage of embryogenesis is described. The frequency of sister chromatid exchanges in such differentiated chromosomes was calculated.

[The modelling of the genetic correction of familial hypercholesterolemia by creating cellular clones stably expressing the human low-density lipoprotein receptor]

The stable expression of human low-density lipoprotein receptor (rLDL) was studied in Chinese hamster ovary (CHO) cells transformed by the pMSVL recombinant plasmid. This plasmid contains full-length rLDL cDNA and hybrid promoter consisting of regulatory elements from early SV-40 promoter and glucocorticoid responsive enhancer of Moloney sarcoma virus. The expression of rLDL cDNA in transformed cells was demonstrated using RNA-cDNA blot hybridization, PCR analysis, and immunofluorescent analysis.

[Cytological study of the nucleolus organizer regions in the chromosomes of CBA and C57BL mice and their hybrids]

Transcriptionally active NORs of chromosomes visualized by AgNO3 staining were studied in bone marrow and embryos (day 10 of gestation) of CBA and C57BL mice, as well as of (CBA x C57BL)F1 hybrids. These mouse strains were shown to differ by the average number of Ag-positive NORs in marrow cells; in hybrids, the number of NORs is greater than in the parent strains. During embryogenesis, the number of chromosomes carrying silver-stained NORs increases; however, no significant differences by this parameter was detected between hybrid and C57BL embryos. The average number of silver-stained NORs was the smallest in embryos of CBA mice.

[Expression of ceruloplasmin gene in mammalian organs from the data of hybridization analysis with complementary DNA probes]

Expression of ceruloplasmin (Cp)-coding gene in rat and human liver and brain tissues was studied by Northern blot hybridization and by in situ hybridization with cloned species-specific cDNA probes. In rat brain structures, different levels of Cp mRNA were detected, the maximal one was found in cerebellum. The steady-state level of Cp mRNA in rat and human brain was several times lower than in parenchymatous liver cells. The size heterogeneity of Cp mRNA was found. Polyadenylated RNA prepared from human liver contains two equally abundant Cp mRNAs differing in their chain length (3.6 and 4.5 kb) while brain polyadenylated RNA contains a single Cp mRNA (4.5 kb).

[An analysis of the action of nonspecific and restriction nucleases on metaphase chromosomes in situ]

Patterns of differential staining of Drosophila, mouse, rat, cattle and pig chromosomes were examined after the treatment with nucleases (DNAase I, DNAase II) and restriction enzymes (AluI, HpaII, MspI, BpE, EcoRI). The above effects depend on the species used, on the enzymes and substitution of thymine for bromodeoxyuridine in the chromosomal DNA. It is supposed that such a phenomenon may not only result from the irregular distribution of specific restriction sites along chromosomes but also depend on the specificity of supramolecular organization of the chromosomal DNA.

[Detection of active genes in mouse metaphase chromosomes using DNAse I in situ]

The active genes of rRNA were localized near the centromere region of metacentric translocation chromosome Rb(9, 19) 163H in early mouse embryos revealed by differential silver staining of NORs. Using nick-translation reaction in situ it was shown that rRNA genes in metaphase chromosomes were in a deoxyribonuclease I sensitive conformation. This method of nick-translation in situ can be used for visualization of various actively transcribed regions of genome at metaphase.

[Nucleolus organizer regions of chromosomes in early embryogenesis of laboratory mice]

Selective silver staining was used to study optimal conditions for demonstration of nucleolus organizer regions (NORs) of chromosomes in early embryogenesis of the laboratory mouse. The NORs were not observable during the first cleavage division. During the second cleavage, 1-7 NORs per metaphase were demonstrable. The time course of NORs demonstration was elucidated from the first cleavage till the 10th day of gestation.

[Study, on isolated nuclei, of the dynamics of chromosome changes in female germ cells in early human embryos]

Sixteen human female embryos at the age of 33-35 days and 7, 9, 10, 11 weeks of development have been studied. Isolated nuclei of the sex and somatic cells have been obtained from embryonic gonads. Total air-dried preparations have been stained with fluorochrome "Hoechst 33258" and studied under the luminescent microscope. In the nuclei of gonocytes, at the moment when incorporation into the gonad takes place, sex chromatin, as well as structural heterochromatin, is absent. Beginning from the oogonia stage up to the preleptotene, a progressive condensation of chromatin is observed; heterocyclic X chromosome appears. When the preleptotene is completed, heterochromatized x chromosome disappears.

[Change in the gonocytic nucleĭ at different stages of their differentiation in early human female embryos]

Fourteen human female embryos at the age of 18, 32, 33 days and 6, 7, 9, 10, 11 weeks fixed in Carnoy's fluid and in 12% neutral formalin have been studied. Paraffin sections stained with hematoxylin, methyl green - pyronine were examined under light microscope. Staining with fluorochrome Xexct 33258" was applied for luminescent microscopy. Gonocyte nuclei both localized in the wall of yolk sac and during their migration differ from somatic cells by "blasomere" type of their nucleus organization. During this stage of development, gonocyte nuclei have no sex chromatin, although it is distinctly detected in the nuclei of surrounding somatic cells in the same embryos. After the gonocytes had contacts with "germinal" epithelium, heterochromatization of one X-chromosome occurs. Sex chromatin is preserved in the nuclei of oogonia disappearing in the course of preleptotene. At differentiation in oogonia, the nucleus of sex chromatin and the structure of their chromatin undergo certain changes.