Chromatin remodeling in oligodendrogenesis.

Oligodendrocytes are one type of glial cells responsible for myelination and providing trophic support for axons in the central nervous system of vertebrates. Thanks to myelin, the speed of electrical-signal conduction increases several hundred-fold because myelin serves as a kind of electrical insulator of nerve f ibers and allows for quick saltatory conduction of action potentials through Ranvier nodes, which are devoid of myelin. Given that different parts of the central nervous system are myelinated at different stages of development and most regions contain both myelinated and unmyelinated axons, it is obvious that very precise mechanisms must exist to control the myelination of individual axons. As they go through the stages of specif ication and differentiation - from multipotent neuronal cells in the ventricular zone of the neural tube to mature myelinating oligodendrocytes as well as during migration along blood vessels to their destination - cells undergo dramatic changes in the pattern of gene expression. These changes require precisely spatially and temporally coordinated interactions of various transcription factors and epigenetic events that determine the regulatory landscape of chromatin. Chromatin remodeling substantially affects transcriptional activity of genes. The main component of chromatin is the nucleosome, which, in addition to the structural function, performs a regulatory one and serves as a general repressor of genes. Changes in the type, position, and local density of nucleosomes require the action of specialized ATPdependent chromatin-remodeling complexes, which use the energy of ATP hydrolysis for their activity. Mutations in the genes encoding proteins of the remodeling complexes are often accompanied by serious disorders at early stages of embryogenesis and are frequently identif ied in various cancers. According to the domain arrangement of the ATP-hydrolyzing subunit, most of the identif ied ATP-dependent chromatin-remodeling complexes are classif ied into four subfamilies: SWI/SNF, CHD, INO80/SWR, and ISWI. In this review, we discuss the roles of these subunits of the different subfamilies at different stages of oligodendrogenesis.

Social defeat stress in adult mice causes alterations in gene expression, alternative splicing, and the epigenetic landscape of H3K4me3 in the prefrontal cortex: An impact of early-life stress.

Chronic stress is the leading risk factor of a broad range of severe psychopathologies. Nonetheless, the molecular mechanisms triggering these pathological processes are not well understood. In our study, we investigated the effects of 15-day social defeat stress (SDS) on the genome-wide landscape of trimethylation at the 4th lysine residue of histone H3 (H3K4me3) and on the transcriptome in the prefrontal cortex of mice that were reared normally (group SDS) or subjected to maternal separation early in life (group MS+SDS). The mice with the history of stress early in life showed increased susceptibility to SDS in adulthood and demonstrated long-lasting genome-wide alterations in gene expression and splicing as well as in the H3K4me3 epigenetic landscape in the prefrontal cortex. Thus, the high-throughput techniques applied here allowed us to simultaneously detect, for the first time, genome-wide epigenetic and transcriptional changes in the murine prefrontal cortex that are associated with both chronic SDS and increased susceptibility to this stressor.

Data of correlation analysis between the density of H3K4me3 in promoters of genes and gene expression: Data from RNA-seq and ChIP-seq analyses of the murine prefrontal cortex.

H3K4me3 is typically found in the promoter region of genes and is a mark associated with an open chromatin state and active gene transcription. Nonetheless, the role of H3K4me3 in the regulation of transcription is still debated. To improve the understanding of the connection between H3K4me3 density in promoters and gene expression, we assessed the correlation between these two parameters. We utilized genome-wide high-throughput RNA sequencing (RNA-seq) data and H3K4me3-based chromatin immunoprecipitation with high-throughput sequencing (ChIP-seq), carried out on the same samples of the prefrontal cortex from 10 male C57Bl6 mice with different stress experience [Social defeat stress in adult mice causes alterations in gene expression, alternative splicing, and the epigenetic landscape of H3K4me3 in the prefrontal cortex: an impact of early-life stress, 1]. In addition, we assessed the correlation between H3K4me3 density and gene expression in datasets of cell-specific genes. Altogether, the results are useful for the elucidation of H3K4me3 involvement in the regulation of transcription in the murine prefrontal cortex.

Evaluation of various RNA-seq approaches for identification of gene outrons in the flatworm Opisthorchis felineus.

The parasitic flatworm Opisthorchis felineus is one of the causative agents of opisthorchiasis in humans. Recently, we assembled the O. felineus genome, but the correct genome annotation by means of standard methods was hampered by the presence of spliced leader trans-splicing (SLTS). As a result of SLTS, the original 5'-end (outron) of the transcripts is replaced by a short spliced leader sequence donated from a specialized SL RNA. SLTS is involved in the RNA processing of more than half of O. felineus genes, making it hard to determine the structure of outrons and bona fide transcription start sites of the corresponding genes and operons, being based solely on mRNA-seq data. In the current study, we tested various experimental approaches for identifying the sequences of outrons in O. felineus using massive parallel sequencing. Two of them were developed by us for targeted sequencing of already processed branched outrons. One was based on sequence-specific reverse transcription from the SL intron toward the 5'-end of the Y-branched outron. The other used outron hybridization with an immobilized single-stranded DNA probe complementary to the SL intron. Additionally, two approaches to the sequencing of rRNA-depleted total RNA were used, allowing the identification of a wider range of transcripts compared to mRNAseq. One is based on the enzymatic elimination of overrepresented cDNAs, the other utilizes exonucleolytic degradation of uncapped RNA by Terminator enzyme. By using the outron-targeting methods, we were not able to obtain the enrichment of RNA preparations by processed outrons, which is most likely indicative of a rapid turnover of these trans-splicing intermediate products. Of the two rRNA depletion methods, a method based on the enzymatic normalization of cDNA (Zymo-Seq RiboFree) showed high efficiency. Compared to mRNA-seq, it provides an approximately twofold increase in the fraction of reads originating from outrons and introns. The results suggest that unprocessed nascent transcripts are the main source of outron sequences in the RNA pool of O. felineus.

Mechanisms of Brain Glucocorticoid Resistance in Stress-Induced Psychopathologies.

Exposure to stress activates the hypothalamic-pituitary-adrenal axis and leads to increased levels of glucocorticoid (GC) hormones. Prolonged elevation of GC levels causes neuronal dysfunction, decreases the density of synapses, and impairs neuronal plasticity. Decreased sensitivity to glucocorticoids (glucocorticoid resistance) that develops as a result of chronic stress is one of the characteristic features of stress-induced psychopathologies. In this article, we reviewed the published data on proposed molecular mechanisms that contribute to the development of glucocorticoid resistance in brain, including changes in the expression of the glucocorticoid receptor (GR) gene, biosynthesis of GR isoforms, and GR posttranslational modifications. We also present data on alterations in the expression of the FKBP5 gene encoding the main component of cell ultra-short negative feedback loop of GC signaling regulation. Recent discoveries on stress- and GR-induced changes in epigenetic modification patterns as well as normalizing action of antidepressants are discussed. GR and FKBP5 gene polymorphisms associated with stress-induced psychopathologies are described, and their role in glucocorticoid resistance is discussed.

[Pro-aggressive effect of diazepam in male mice with repeated experience of aggression].

Previous studies have reported that repeated experience of aggression is attended with the development of increased anxiety in male mice. The paper aimed to investigate effect of anxiolytic, diazepam, on the level of anxiety and aggression in these animals. The drug was chronically administrated for two weeks at the process of aggression experience acquisition. It was shown that diazepam decreased anxiety but didn't influence aggression level assessed by total time of attacks. However, diazepam decreased demonstration of aggressive grooming in part of aggressive males. Group of diazepam-treated aggressive males which displayed aggressive grooming didn't differ in level of anxiety and aggression in saline-treated male mice. Diazepam had anxiolytic and pro-aggressive effects in male mice without demonstrating aggressive grooming. Thus, we can conclude that anxiolytic effect of diazepam is accompanied with increased aggression as side effect in some male mice which have repeated experience of aggression.

[Effects of diazepam on mixed anxiety/depression state in male mice].

Chronic social defeat stress in daily agonistic interactions leads to the development of mixed anxiety/depression state in male mice. This paper aimed to study the effects of chronic diazepam treatment on the psychoemotional state of these animals. Diazepam (0.5 mg/kg, i/p, Polfa Tarchomin S. A.) or saline was chronically injected into male mice for two weeks on the background of continuing agonistic interactions (preventive treatment) or into male mice with mixed anxiety/depression state after stopping of social confrontations (therapeutic treatment). Then, the animals were studied in the partition, plus-maze and Porsolt' tests, estimating the levels of communicativeness, anxiety and depressiveness, respectively. Preventive diazepam treatment had a weak protective anxiolytic and pro-depressive effect. The therapeutic diazepam treatment didn't influence on the anxiety and depression-like state. Chronic diazepam was ineffective for the treatment of the mixed anxiety/depression state in male mice. Different effects ofdiazepam on anxiety and depression-like states under preventive treatment confirmed our conclusion shown earlier about the independent development of these pathologies at least in our experimental paradigm.

[Effect of mu- and kappa-opioid receptor antagonists on aggressiveness of male mice with repeated experience of aggression].

Mu and kappa opioid receptors often show opposite actions in the regulation ofphysiological functions and behaviors including aggressive behavior. In the present study, effects ofmu antagonist CTAP (1 and 2 mg/kg, sc) and kappa antagonist nor-BNI (0.5 mg/kg, sc) on the manifestation of aggressive behavior of C57BL/6J male mice with a short (3 days) and a long (20 days) experience of victories in daily intermale confrontations were investigated. It was shown that the mice with a short experience of aggression are tolerant to blockade of both mu and kappa opioid receptors. In the mice with a long experience of aggression, CTAP increased latency of aggression in dose-dependent manner, but did not change the duration of attacks. Nor-BNI had no influence on the behavior of the male mice with a long experience of aggression in the intermale confrontation. The possible changes in opioid receptor sensitivity in C57BL/6J male mice under the influence ofa long experience of aggression are discussed.

Cell cycle arrest in the thymus and spleen in male mice under conditions of chronic social defeat stress: effects of diazepam.

The effects of chronic social defeat stress on the percentage of cells in different phases of the cell cycle and in apoptosis in the thymus and spleen of male mice were studied by the method of flow cytofluorometry. In stressed males, thymus weight decreased, the percent of proliferating thymocytes was significantly lower, and the percentage of G0-G1 cells was higher than in intact males. Stress substantially reduced the percentage of splenocytes in the G0-G1 phase and apoptotic cells, but the percentage of S and G2-M cells and proliferation index significantly increased. Chronic administration of anxiolytic diazepam prevented the majority of the changes in the percentage of cells in different phases of the cell cycle, but apoptosis in the thymus increased under these conditions. Possible association between cell cycle disorders, impairment of cell immunity, and chronic anxiety developing under conditions of long-term social defeat stress is considered.

[Effect of sodium valproate on aggressive behavior of male mice with various aggression experience].

Sector of Social Behavior Neurogenetics, Institute of Cytology and Genetics, Siberian Branch, Effects of sodium valproate on the aggressive behavior of male mice with 2- and 20-day positive fighting experience have been studied. It is established that valproate administered in a singe dose of 100 mg/kg has no effect on the behavior of male mice with a 2-day experience of aggression. The treatment of mice with 300 mg/kg of valproate significantly decreased the level of aggressive motivation and the percentage of animals demonstrating attacks and threats. In male mice with a 20-day experience of aggression, valproate decreased the time of hostile behavior in a dose-dependent manner. Valproate in a single dose of 300 mg/kg significantly decreased the level of aggressive motivation, but also produced a toxic effect, whereby 73% of aggressive males demonstrated long-term immobility and 45% exhibited movement abnormalities (falls) upon the treatment. It is suggested that changes in the brain neurochemical activity, which are caused by a prolonged experience of aggression, modify the effects of sodium valproate.

[Decrease in sucrose solution consumption by CBA/Lac male mice under chronic social stress].

The influence of repeated experience of social defeats in daily agonistic interactions on voluntary consumption of 1% sucrose solution supplemented with vanillin (0.2%) was studied in male mice of CBA/Lac strain with genetic predisposition to catalepsy as compared to depression-predisposed C57BL/6J mice. Intact mice of both strains prefered sucrose solution to water under conditions of two-bottle free choice. Sucrose solution intake was shown to decrease in losers of both strains exposed to social confrontations as compared to controls. It was suggested that the high level of anxiety revealed in mice of both strains can be the determining factor of the decrease in sucrose solution consumption under conditions of chronic social stress.

[Effect of positive and negative social experiences on sucrose solution intake by male mice].

Hedonic reactions to various rewards play a key role in various forms of motivated behavior. The influence of repeated experience of social victories or defeats in daily agonistic interactions between male mice on voluntary consumption of 1% sucrose solution supplemented with vanillin (0.2%) was studied. Intake of sucrose solution was shown to be decreased in the winners and losers exposed to social confrontations as compared with the controls. Three days of deprivation restored the intake of sucrose solution to the control level in the winners and failed to restore the baseline intake in the losers. The results imply that similar reaction of animals to a hedonic non-drug reinforcer may have different motivational origin depending on positive or negative social experience.

Behavioral effect of terahertz waves in male mice.

We studied the effect of terahertz waves (3.6 THz, 81.5 micro, 15 mW) on the behavior of mice. The mice perceived terahertz waves even after short-term exposure (15 min). The effect of terahertz waves was maximum in direct contact of the mice with the laser. Increased anxiety of experimental animals was observed on the next day after 30-min irradiation.

[Influence of experimental context on the development of anhedonia in male mice exposed to chronic social stress].

Consumption of 1% sucrose solution supplemented with 0.2% vanillin was studied in two experimental contexts in male mice living under chronic social stress induced by daily experience of defeats in agonistic interactions and leading to development of depression. In the first experiment, vanillin sucrose solution was made available as an option along with water during 10 days for mice living in group home cages. Then the mice were subjected to repeated social defeat stress and during exposure to stress they were provided with both vanillin sucrose solution and water using a free two-bottle choice paradigm. In the other experiment, vanillin sucrose solution was first offered to mice after 8 days of exposure to social defeat stress. Males familiar with vanillin sucrose solution showed vanillin sucrose preference while experiencing defeat stress: consumption of vanillin sucrose solution was about 70% of total liquid consumption. However, the consumption of vanillin sucrose solution per gram of body weight in mice exposed to social stress during 20 days was significantly lower than in control males. In the second experiment, males after 8 days of social defeat stress were found to consume significantly less vanillin sucrose solution as compared to control males. On average, during two weeks of measurements, vanillin sucrose solution intake was less than 20% of total liquid consumption in males. Consumption per gram of body weight also appeared to be significantly lower than in control group. The influence of experimental context on the development of anhedonia measured as a reduction of sucrose solution intake by chronically stressed male mice is discussed.

An experimental approach for the study of psychotropic drug effects under simulated clinical conditions.

The sensory contact model can induce various different psychopathological states in male mice (anxious depression, catalepsy, social withdrawal, pathological aggression, cognition disturbances, anhedonia, alcoholism etc.). Additionally, this model facilitates the screening of drugs for therapeutic properties, preventive properties and efficiency under simulated clinical conditions. This approach can reveal the action of drugs at different stages of disease development. It is proposed that this pharmacological approach can be applied for the screening of various novel psychotropic drugs.

[Development of anhedonia under negative experience of social confrontations in male mice].

Possible development of anhedonia in male mice under chronic stress produced by social confrontations was investigated. Cheese, instead of traditional sucrose solution, was used as a positive reinforcement. It has been shown that the controls, the winners with repeated experience of aggression accompanied by victories and the losers with repeated experience of social defeats, irrespective of their social status, preferred to eat cheese, but not pellets, under the free choice conditions--80% of total food. After three days of cheese deprivation, the least food motivation and the least level of cheese consumption were observed in the losers as compared with the controls and winners. Influence of social stress as well as negative psychoemotional state produced by social defeats, on development of anhedonia as a symptom of major depression, is discussed.

[Impaired social recognition in male mice with repeated experience of aggression].

Social recognition is crucial for many aspects of animal behavior in stabilized population. Preliminary data proposed impairment of social recognition in male mice with long experience of aggression. To check this hypothesis, experiments with male mice with different aggressive experience (during 2 and 20 days) were performed. Two types of losers were used as partners: losers with active defense reactions and losers displaying submissive postures. The enhanced aggressive motivation was found in both groups of aggressors. Mice with short aggressive experience demonstrated intensive attacks toward the active losers and decreased aggression directed to submissive losers. Mice with long aggressive experience did not change their behavior depending on a type of the partner and displayed a high level of aggression as a result of dominant aggressive motivation and impaired social recognition.

The effects of the D1 receptor antagonist SCH-23390 on individual and aggressive behavior in male mice with different experience of aggression.

The dopaminergic systems of the brain are known to be involved in the mechanisms of aggression. The present report describes studies of the effects of acute administration of the dopamine D1 receptor antagonist SCH-23390 (0.1 mg/kg, i.p., over 30 min) on the individual and aggressive behavior of male mice of the line C57BL/6J with different experience of aggression. A group of animals with no previous experience of aggression responded to administration of this agent with decreases in direct aggression (attacks), though the total time of hostile behavior, i.e., the sum of the durations of attacks, aggressive grooming, and scattering of foreign litter, showed no change. The agent had no effect on the aggressivity of animals with 20 days of experience of agonistic confrontations. The discussion addresses the possible development of pharmacological densensitization of dopamine D1 receptors in aggressive males in response to prolonged activation of the dopaminergic systems in conditions of repeated experience of aggression, as demonstrated previously.

[Choice of "control" in experimental researches of animal social interactions in mice].

The purpose of the present experiment was to clarify the individuals as an appropriate "control" in research of social interactions in animals. As it has been established for the C57BL/6J mouse strain, the best control animals are individually housed for 5 days males in contrast to males placed with females or with other males in groups of 3-10 mice. Such male mice were less anxious and had high exploratory and motor activities in the elevated plus-maze, open-field, forced swimming and exploratory-activity tests.

[Dynamic changes of brain serotonergic and dopaminergic activities during development of anxious depression: experimental study]. / Dinamicheskue izmeneniia serotonergicheskoi i dofaminergicheskoi aktivnosti mozga v protsesse razvitiia trevozhnoi depressii: éksperimental'noe issledovanie.

Chronic psychoemotional stress of social defeats produces development of experimental anxious depression in male mice similar to this disorder in humans. 5-HT and 5-HIAA levels, TPH and MAO A activities, 5-HT1A-receptors in different brain areas were investigated at different stages of development of experimental disorder. It has been shown that initial stage (3 days of social stress) is accompanied by increase of 5-HT level in some brain areas. Decreased 5-HIAA levels in the hippocampus, amygdala and nucleus accumbens were discovered at the stage of forming depression (10 days of social stress). Pharmacological desensitisation and decreased number of 5-HT1A-receptors were shown in frontal cortex and amygdala. At the stage of pronounced depression (20 days of stress), there were no differences in 5-HT and 5-HIAA levels in all brain areas (excluding hypothalamus) of depressive animals. However increased number of 5-HT1A-receptors and decreased affinity in amygdala and decreased TPH and MAOA activities in hippocampus were found in depressive mice. Hypofunction of serotonergic system is suggested at the stage of pronounced depression state in animals. Similar processes had place in brain dopaminergic systems. It is concluded that dynamic changes of brain monoaminergic activities accompany the development of anxious depression in animals. Various parameters of monoaminergic systems are differently changed depending on brain area, mediator system and stage of disorder.