Role of DNA methylation and the DNA methyltransferases in learning and memory

Epigenetic Processes of DNA Methylation Are Selectively Involved in the Mechanisms of Retrograde and Anteograde Amnesia

The participation of DNA methylation processes in the mechanisms of anterograde and retrograde amnesia caused by impaired reconsolidation of conditioned food aversion memory by NMDA glutamate receptor antagonists or serotonin receptor antagonists, respectively, were studied on grape snails. Anterograde amnesia was characterized by impaired formation of long-term memory during repeated learning. Administration of a DNA methyltransferase (DNMT) inhibitor to amnestic animals resulted in accelerated formation of long-term memory during 1 day of repetitive training vs 3 days during initial training. In serotonin-dependent retrograde amnesia, repeated learning without DNMT inhibitor administration or after inhibitor injections led to the formation of long-term memory. The dynamics of memory formation was similar in both cases and did not differ from that during the initial training: the memory was formed within 3 days of training. Thus, epigenetic processes of DNA methylation are selectively involved in the mechanisms of anterograde amnesia, but do not participate in the mechanisms of retrograde amnesia.

DNA Methylation in Alcohol Use Disorder

Excessive drinking damages the central nervous system of individuals and can even cause alcohol use disorder (AUD). AUD is regulated by both genetic and environmental factors. Genes determine susceptibility to alcohol, and the dysregulation of epigenome drives the abnormal transcription program and promotes the occurrence and development of AUD. DNA methylation is one of the earliest and most widely studied epigenetic mechanisms that can be inherited stably. In ontogeny, DNA methylation pattern is a dynamic process, showing differences and characteristics at different stages. DNA dysmethylation is prevalent in human cancer and alcohol-related psychiatric disorders, resulting in local hypermethylation and transcriptional silencing of related genes. Here, we summarize recent findings on the roles and regulatory mechanisms of DNA methylation, the development of methyltransferase inhibitors, methylation alteration during alcohol exposure at different stages of life, and possible therapeutic options for targeting methylation in human and animal studies.

Epidrugs in the Therapy of Central Nervous System Disorders: A Way to Drive on?

The polygenic nature of neurological and psychiatric syndromes and the significant impact of environmental factors on the underlying developmental, homeostatic, and neuroplastic mechanisms suggest that an efficient therapy for these disorders should be a complex one. Pharmacological interventions with drugs selectively influencing the epigenetic landscape (epidrugs) allow one to hit multiple targets, therefore, assumably addressing a wide spectrum of genetic and environmental mechanisms of central nervous system (CNS) disorders. The aim of this review is to understand what fundamental pathological mechanisms would be optimal to target with epidrugs in the treatment of neurological or psychiatric complications. To date, the use of histone deacetylases and DNA methyltransferase inhibitors (HDACis and DNMTis) in the clinic is focused on the treatment of neoplasms (mainly of a glial origin) and is based on the cytostatic and cytotoxic actions of these compounds. Preclinical data show that besides this activity, inhibitors of histone deacetylases, DNA methyltransferases, bromodomains, and ten-eleven translocation (TET) proteins impact the expression of neuroimmune inflammation mediators (cytokines and pro-apoptotic factors), neurotrophins (brain-derived neurotropic factor (BDNF) and nerve growth factor (NGF)), ion channels, ionotropic receptors, as well as pathoproteins (β-amyloid, tau protein, and α-synuclein). Based on this profile of activities, epidrugs may be favorable as a treatment for neurodegenerative diseases. For the treatment of neurodevelopmental disorders, drug addiction, as well as anxiety disorders, depression, schizophrenia, and epilepsy, contemporary epidrugs still require further development concerning a tuning of pharmacological effects, reduction in toxicity, and development of efficient treatment protocols. A promising strategy to further clarify the potential targets of epidrugs as therapeutic means to cure neurological and psychiatric syndromes is the profiling of the epigenetic mechanisms, which have evolved upon actions of complex physiological lifestyle factors, such as diet and physical exercise, and which are effective in the management of neurodegenerative diseases and dementia.

On the origin and nature of nongenetic information in eumetazoans

Nongenetic information implies all the forms of biological information not related to genes and DNA in general. Despite the deep scientific relevance of the concept, we currently lack reliable knowledge about its carriers and origins; hence, we still do not understand its true nature. Given that genes are the targets of nongenetic information, it appears that a parsimonious approach to find the ultimate source of that information is to trace back the sequential steps of the causal chain upstream of the target genes up to the ultimate link as the source of the nongenetic information. From this perspective, I examine seven nongenetically determined phenomena: placement of locus-specific epigenetic marks on DNA and histones, changes in snRNA expression patterns, neural induction of gene expression, site-specific alternative gene splicing, predator-induced morphological changes, and cultural inheritance. Based on the available evidence, I propose a general model of the common neural origin of all these forms of nongenetic information in eumetazoans.

Pilot Study of the Long-Term Effects of Radiofrequency Electromagnetic Radiation Exposure on the Mouse Brain

The increasing radiofrequency (RF) electromagnetic radiation pollution resulting from the development and use of technologies utilizing RF has sparked debate about the possible biological effects of said radiation. Of particular concern is the potential impact on the brain, due to the close proximity of communication devices to the head. The main aim of this study was to examine the effects of long-term exposure to RF on the brains of mice in a real-life scenario simulation compared to a laboratory setting. The animals were exposed continuously for 16 weeks to RF using a household Wi-Fi router and a laboratory device with a frequency of 2.45 GHz, and were compared to a sham-exposed group. Before and after exposure, the mice underwent behavioral tests (open-field test and Y-maze); at the end of the exposure period, the brain was harvested for histopathological analysis and assessment of DNA methylation levels. Long-term exposure of mice to 2.45 GHz RF radiation increased their locomotor activity, yet did not cause significant structural or morphological changes in their brains. Global DNA methylation was lower in exposed mice compared to sham mice. Further research is needed to understand the mechanisms behind these effects and to understand the potential effects of RF radiation on brain function.

The Emerging Role of Epigenetics in Metabolism and Endocrinology

Each cell in a multicellular organism has its own phenotype despite sharing the same genome. Epigenetics is a somatic, heritable pattern of gene expression or cellular phenotype mediated by structural changes in chromatin that occur without altering the DNA sequence. Epigenetic modification is an important factor in determining the level and timing of gene expression in response to endogenous and exogenous stimuli. There is also growing evidence concerning the interaction between epigenetics and metabolism. Accordingly, several enzymes that consume vital metabolites as substrates or cofactors are used during the catalysis of epigenetic modification. Therefore, altered metabolism might lead to diseases and pathogenesis, including endocrine disorders and cancer. In addition, it has been demonstrated that epigenetic modification influences the endocrine system and immune response-related pathways. In this regard, epigenetic modification may impact the levels of hormones that are important in regulating growth, development, reproduction, energy balance, and metabolism. Altering the function of the endocrine system has negative health consequences. Furthermore, endocrine disruptors (EDC) have a significant impact on the endocrine system, causing the abnormal functioning of hormones and their receptors, resulting in various diseases and disorders. Overall, this review focuses on the impact of epigenetics on the endocrine system and its interaction with metabolism.

DNA methylation inhibition participates in the anterograde amnesia key mechanism through the suppression of the transcription of genes involved in memory formation in grape snails

The study of the amnesia mechanisms is of both theoretical and practical importance. The mechanisms of anterograde amnesia are the least studied, due to the lack of an experimental model that allows studying this amnesia type molecular and cellular mechanisms. Previously, we found that conditional food aversion memory reconsolidation impairment in snails by NMDA glutamate receptor antagonists led to the amnesia induction, in the late stages of which (>10 days) repeated training did not cause long-term memory formation. In the same animals, long-term memory aversion to a new food type was formed. We characterized this amnesia as specific anterograde amnesia. In the present work we studied the role of epigenetic DNA methylation processes as well as protein and mRNA synthesis in the mechanisms of anterograde amnesia and memory recovery. DNMT methyltransferase inhibitors (iDNMT: zebularine, RG108 (N-Phthalyl-1-tryptophan), and 5-AZA (5-Aza-2'-deoxycytidine)) were used to alter DNA methylation. It was found that in amnesic animals the iDNMT administration before or after shortened repeated training led to the rapid long-term conditional food aversion formation (Ebbinghaus saving effect). This result suggests that amnestic animals retain a latent memory, which is the basis for accelerated memory formation during repeated training. Protein synthesis inhibitors administration (cycloheximide) before or immediately after repeated training or administration of RNA synthesis inhibitor (actinomycin D) after repeated training prevented memory formation under iDNMT action. The earlier protein synthesis inhibitor effect suggests that the proteins required for memory formation are translated from the pre-existing, translationally repressed mRNAs. Thus, we have shown for the first time that the anterograde amnesia key mechanism is DNMT-dependent suppression of the transcription of genes involved in memory mechanisms. Inhibition of DNMT during repeated training reversed these genes expression blockade, opening access to them by transcription factors synthesized during training from the pre-existing mRNAs.

Genes and pathways associated with fear discrimination identified by genome-wide DNA methylation and RNA-seq analyses in nucleus accumbens in mice

Fear memory is critical for individual survival. However, the maladaptive fear response is one of the hallmarks of fear-related disorders, which is characterized by the failure to discriminate threatening signals from neutral or safe cues. The biological mechanisms of fear discrimination remain to be clarified. In this study, we found that the nucleus accumbens (NAc) was indispensable for the formation of cued fear memory in mice, during which the expression of DNA methyltransferase 3a gene (DNMT3a) increased. Injection of Zebularine, a nonspecific DNMT inhibitor, into NAc immediately after conditioning induced a maladaptive fear response to neutral cue (CS^-). Using whole-genome bisulfite sequencing (WGBS), differentially methylated sites and methylated regions (DMRs) were investigated. 16,226 DMRs in the genenome were identified, in which, 214 genes with significant differences in their methylation levels and mRNA expression profiles were identified through correlation analysis. Notably, 15 genes were synaptic function-related and 8 genes were enriched in the cGMP-PKG signaling pathway. Moreover, inhibition of PKG impaired fear discrimination. Together, our results revealed the profile and role of genome-wide DNA methylation in NAc in the regulation of fear discrimination.

Epigenetics in fetal alcohol spectrum disorder

During pregnancy, alcohol abuse and its detrimental effects on developing offspring are major public health, economic and social challenges. The prominent characteristic attributes of alcohol (ethanol) abuse during pregnancy in humans are neurobehavioral impairments in offspring due to damage to the central nervous system (CNS), causing structural and behavioral impairments that are together named fetal alcohol spectrum disorder (FASD). Development-specific alcohol exposure paradigms were established to recapitulate the human FASD phenotypes and establish the underlying mechanisms. These animal studies have offered some critical molecular and cellular underpinnings likely to account for the neurobehavioral impairments associated with prenatal ethanol exposure. Although the pathogenesis of FASD remains unclear, emerging literature proposes that the various genomic and epigenetic components that cause the imbalance in gene expression can significantly contribute to the development of this disease. These studies acknowledged numerous immediate and enduring epigenetic modifications, such as methylation of DNA, post-translational modifications (PTMs) of histone proteins, and regulatory networks related to RNA, using many molecular approaches. Methylated DNA profiles, PTMs of histone proteins, and RNA-regulated expression of genes are essential for synaptic and cognitive behavior. Thus, offering a solution to many neuronal and behavioral impairments reported in FASD. In the current chapter, we review the recent advances in different epigenetic modifications that cause the pathogenesis of FASD. The information discussed can help better explain the pathogenesis of FASD and thereby might provide a basis for finding novel therapeutic targets and innovative treatment strategies.

Comparative Study of the Effect of a DNA Methyltransferase Inhibitor and a Histone Deacetylase Inhibitor on Memory Formation Processes in Anterograde Amnesia

The participation of DNA methylation and histone acetylation in the mechanisms of anterograde amnesia and memory recovery was studied on grape snails trained in conditioned food aversion. Anterograde amnesia developed 10 days after memory reconsolidation impairment with an NMDA glutamate receptor antagonist and was characterized by long-term memory formation impairment upon repeated training. DNA methyltransferase inhibitor injections to snails 1 h before repeated training, as well as 15 min or 4 h after repeated training, caused rapid formation of memory that persisted for at least 10 days. Injections of histone deacetylase inhibitor before repeated training also induced the formation of a stable long-term memory. However, administration of histone deacetylase inhibitor 15 min after repeated training initiated a temporary memory recovery. Injections of the inhibitor 4 h after repeated training were ineffective. These results indicate that histone-dependent chromatin remodeling and DNA methylation are selectively involved in the mechanisms of anterograde amnesia and memory recovery.

The new mechanism of cognitive decline induced by hypertension: High homocysteine-mediated aberrant DNA methylation

The prevalence and severity of hypertension-induced cognitive impairment increase with the prolonging of hypertension. The mechanisms of cognitive impairment induced by hypertension primarily include cerebral blood flow perfusion imbalance, white and gray matter injury with blood–brain barrier disruption, neuroinflammation and amyloid-beta deposition, genetic polymorphisms and variants, and instability of blood pressure. High homocysteine (HHcy) is an independent risk factor for hypertension that also increases the risk of developing early cognitive impairment. Homocysteine (Hcy) levels increase in patients with cognitive impairment induced by hypertension. This review summarizes a new mechanism whereby HHcy-mediated aberrant DNA methylation and exacerbate hypertension. It involves changes in Hcy-dependent DNA methylation products, such as methionine adenosyltransferase, DNA methyltransferases, S-adenosylmethionine, S-adenosylhomocysteine, and methylenetetrahydrofolate reductase (MTHFR). The mechanism also involves DNA methylation changes in the genes of hypertension patients, such as brain-derived neurotrophic factor, apolipoprotein E4, and estrogen receptor alpha, which contribute to learning, memory, and attention deficits. Studies have shown that methionine (Met) induces hypertension in mice. Moreover, DNA hypermethylation leads to cognitive behavioral changes alongside oligodendroglial and/or myelin deficits in Met-induced mice. Taken together, these studies demonstrate that DNA methylation regulates cognitive dysfunction in patients with hypertension. A better understanding of the function and mechanism underlying the effect of Hcy-dependent DNA methylation on hypertension-induced cognitive impairment will be valuable for early diagnosis, interventions, and prevention of further cognitive defects induced by hypertension.

Current understanding of osteoarthritis pathogenesis and relevant new approaches

Osteoarthritis (OA) is the most common degenerative joint disease that causes painful swelling and permanent damage to the joints in the body. The molecular mechanisms of OA are currently unknown. OA is a heterogeneous disease that affects the entire joint, and multiple tissues are altered during OA development. To better understand the pathological mechanisms of OA, new approaches, methods, and techniques need to be used to understand OA pathogenesis. In this review, we first focus on the epigenetic regulation of OA, with a particular focus on DNA methylation, histone modification, and microRNA regulation, followed by a summary of several key mediators in OA-associated pain. We then introduce several innovative techniques that have been and will continue to be used in the fields of OA and OA-associated pain, such as CRISPR, scRNA sequencing, and lineage tracing. Next, we discuss the timely updates concerning cell death regulation in OA pathology, including pyroptosis, ferroptosis, and autophagy, as well as their individual roles in OA and potential molecular targets in treating OA. Finally, our review highlights new directions on the role of the synovial lymphatic system in OA. An improved understanding of OA pathogenesis will aid in the development of more specific and effective therapeutic interventions for OA.

Enriched environment causes epigenetic changes in hippocampus and improves long-term cognitive function in sepsis

Sepsis is defined as a life-threatening organ dysfunction caused by an inappropriate host response to infection. The presence of oxidative stress and inflammatory mediators in sepsis leads to dysregulated gene expression, leading to a hyperinflammatory response. Environmental conditions play an important role in various pathologies depending on the stimulus it presents. A standard environment condition (SE) may offer reduced sensory and cognitive stimulation, but an enriched environment improves spatial learning, prevents cognitive deficits induced by disease stress, and is an important modulator of epigenetic enzymes. The study evaluated the epigenetic alterations and the effects of the environmental enrichment (EE) protocol in the brain of animals submitted to sepsis by cecal ligation and perforation (CLP). Male Wistar rats were divided into sham and CLP at 24 h, 72 h, 10 days and 30 days after sepsis. Other male Wistar rats were distributed in a SE or in EE for forty-five days. Behavioral tests, analysis of epigenetic enzymes:histone acetylase (HAT), histone deacetylase (HDAC) and DNA methyltransferase (DNMT), biochemical and synaptic plasticity analyzes were performed. An increase in HDAC and DNMT activities was observed at 72 h, 10 days and 30 days. There was a positive correlation between epigenetic enzymes DNMT and HDAC 24 h, 10 days and 30 days. After EE, HDAC and DNMT enzyme activity decreased, cognitive impairment was reversed, IL1-β levels decreased and there was an increase in PSD-95 levels in the hippocampus. Interventions in environmental conditions can modulate the outcomes of long-term cognitive consequences associated with sepsis, supporting the idea of the potential benefits of EE.

DNA Methylation-Dependent Gene Expression Regulation of Glutamate Transporters in Cultured Radial Glial Cells

Exposure to xenobiotics has a significant impact in brain physiology that could be liked to an excitotoxic process induced by a massive release of the main excitatory neurotransmitter, L-glutamate. Overstimulation of extra-synaptic glutamate receptors, mainly of the N-methyl-D-aspartate subtype leads to a disturbance of intracellular calcium homeostasis that is critically involved in neuronal death. Hence, glutamate extracellular levels are tightly regulated through its uptake by glial glutamate transporters. It has been observed that glutamate regulates its own removal, both in the short-time frame via a transporter-mediated decrease in the uptake, and in the long-term through the transcriptional control of its gene expression, a process mediated by glutamate receptors that involves the Ca²⁺/diacylglycerol-dependent protein kinase and the transcription factor Ying Yang 1. Taking into consideration that this transcription factor is a member of the Polycomb complex and thus, part of repressive and activating chromatin remodeling factors, it might direct the interaction of DNA methyltransferases or dioxygenases of methylated cytosines to their target sequences. Here we explored the role of dynamic DNA methylation in the expression and function of glial glutamate transporters. To this end, we used the well-characterized models of primary cultures of chick cerebellar Bergmann glia cells and a human retina-derived Müller glia cell line. A time and dose-dependent increase in global DNA methylation was evident upon glutamate exposure. Under hypomethylation conditions, the glial glutamate transporter protein levels and uptake activity were increased. These results favor the notion that a dynamic DNA methylation program triggered by glutamate in glial cells modulates one of its major functions: glutamate removal.

DNA Methylation in Genetic and Sporadic Forms of Neurodegeneration: Lessons from Alzheimer's, Related Tauopathies and Genetic Tauopathies

Genetic and sporadic forms of tauopathies, the most prevalent of which is Alzheimer's Disease, are a scourge of the aging society, and in the case of genetic forms, can also affect children and young adults. All tauopathies share ectopic expression, mislocalization, or aggregation of the microtubule associated protein TAU, encoded by the MAPT gene. As TAU is a neuronal protein widely expressed in the CNS, the overwhelming majority of tauopathies are neurological disorders. They are characterized by cognitive dysfunction often leading to dementia, and are frequently accompanied by movement abnormalities such as parkinsonism. Tauopathies can lead to severe neurological deficits and premature death. For some tauopathies there is a clear genetic cause and/or an epigenetic contribution. However, for several others the disease etiology is unclear, with few tauopathies being environmentally triggered. Here, we review current knowledge of tauopathies listing known genetic and important sporadic forms of these disease. Further, we discuss how DNA methylation as a major epigenetic mechanism emerges to be involved in the disease pathophysiology of Alzheimer's, and related genetic and non-genetic tauopathies. Finally, we debate the application of epigenetic signatures in peripheral blood samples as diagnostic tools and usages of epigenetic therapy strategies for these diseases.

A putative role for lncRNAs in epigenetic regulation of memory

The central dogma of molecular genetics is defined as encoded genetic information within DNA, transcribed into messenger RNA, which contain the instructions for protein synthesis, thus imparting cellular functionality and ultimately life. This molecular genetic theory has given birth to the field of neuroepigenetics, and it is now well established that epigenetic regulation of gene transcription is critical to the learning and memory process. In this review, we address a potential role for a relatively new player in the field of epigenetic crosstalk - long non-coding RNAs (lncRNAs). First, we briefly summarize epigenetic mechanisms in memory formation and examine what little is known about the emerging role of lncRNAs during this process. We then focus discussions on how lncRNAs interact with epigenetic mechanisms to control transcriptional programs under various conditions in the brain, and how this may be applied to regulation of gene expression necessary for memory formation. Next, we explore how epigenetic crosstalk in turn serves to regulate expression of various individual lncRNAs themselves. To highlight the importance of further exploring the role of lncRNA in epigenetic regulation of gene expression, we consider the significant relationship between lncRNA dysregulation and declining memory reserve with aging, Alzheimer's disease, and epilepsy, as well as the promise of novel therapeutic interventions. Finally, we conclude with a discussion of the critical questions that remain to be answered regarding a role for lncRNA in memory.

Perinatal exposure to high fat diet alters expression of MeCP2 in the hypothalamus

Obesity is a complex disease that is the result of a number of different factors including genetic, environmental, and endocrine abnormalities. Given that monogenic forms of obesity are rare, it is important to identify other mechanisms that contribute to its etiology. Methyl-Cp-G binding protein 2 (MeCP2) is a neuroepigenetic factor that binds to methylated regions of DNA to influence transcription. Past studies demonstrate that disruption in MeCP2 function produces obesity in mice. Using a diet-induced obesity mouse model, we show that perinatal exposure to high fat diet significantly decreases MeCP2 protein expression in the hypothalamus of female mice, effects not seen when high fat diet is given to mice during adulthood. Moreover, these effects are seen specifically in a subregion of the hypothalamus known as the arcuate nucleus with females having decreased MeCP2 expression in rostral areas and males having decreased MeCP2 expression in intermediate regions of the arcuate nucleus. Interestingly, mice gain more weight when exposed to high fat diet during adulthood relative to mice exposed to high fat diet perinatally, suggesting that perhaps high fat diet exposure during adulthood may be affecting mechanisms independent of MeCP2 function. Collectively, our data demonstrate that there are developmentally sensitive periods in which MeCP2 expression is influenced by high fat diet exposure and this occurs in a sexually dimorphic manner.

Neurodegenerative movement disorders: An epigenetics perspective and promise for the future

Neurodegenerative movement disorders (NMDs) are age‐dependent disorders that are characterised by the degeneration and loss of neurons, typically accompanied by pathological accumulation of different protein aggregates in the brain, which lead to motor symptoms. NMDs include Parkinson's disease, multiple system atrophy, progressive supranuclear palsy, and Huntington's disease, among others. Epigenetic modifications are responsible for functional gene regulation during development, adult life and ageing and have progressively been implicated in complex diseases such as cancer and more recently in neurodegenerative diseases, such as NMDs. DNA methylation is by far the most widely studied epigenetic modification and consists of the reversible addition of a methyl group to the DNA without changing the DNA sequence. Although this research field is still in its infancy in relation to NMDs, an increasing number of studies point towards a role for DNA methylation in disease processes. This review addresses recent advances in epigenetic and epigenomic research in NMDs, with a focus on human brain DNA methylation studies. We discuss the current understanding of the DNA methylation changes underlying these disorders, the potential for use of these DNA modifications in peripheral tissues as biomarkers in early disease detection, classification and progression as well as a promising role in future disease management and therapy.

Epigenetic regulation in Huntington's disease

Huntington's disease (HD) is a devastating and fatal monogenic neurodegenerative disorder characterized by progressive loss of selective neurons in the brain and is caused by an abnormal expansion of CAG trinucleotide repeats in a coding exon of the huntingtin (HTT) gene. Progressive gene expression changes that begin at premanifest stages are a prominent feature of HD and are thought to contribute to disease progression. Increasing evidence suggests the critical involvement of epigenetic mechanisms in abnormal transcription in HD. Genome-wide alterations of a number of epigenetic modifications, including DNA methylation and multiple histone modifications, are associated with HD, suggesting that mutant HTT causes complex epigenetic abnormalities and chromatin structural changes, which may represent an underlying pathogenic mechanism. The causal relationship of specific epigenetic changes to early transcriptional alterations and to disease pathogenesis require further investigation. In this article, we review recent studies on epigenetic regulation in HD with a focus on DNA and histone modifications. We also discuss the contribution of epigenetic modifications to HD pathogenesis as well as potential mechanisms linking mutant HTT and epigenetic alterations. Finally, we discuss the therapeutic potential of epigenetic-based treatments.

DNA Methylation Signatures of Bone Metabolism in Osteoporosis and Osteoarthritis Aging-Related Diseases: An Updated Review

DNA methylation is one of the most studied epigenetic mechanisms that play a pivotal role in regulating gene expression. The epigenetic component is strongly involved in aging-bone diseases, such as osteoporosis and osteoarthritis. Both are complex multi-factorial late-onset disorders that represent a globally widespread health problem, highlighting a crucial point of investigations in many scientific studies. In recent years, new findings on the role of DNA methylation in the pathogenesis of aging-bone diseases have emerged. The aim of this systematic review is to update knowledge in the field of DNA methylation associated with osteoporosis and osteoarthritis, focusing on the specific tissues involved in both pathological conditions.

DNA Methyltransferase 3A Is Involved in the Sustained Effects of Chronic Stress on Synaptic Functions and Behaviors

Emerging evidence suggests that epigenetic mechanisms regulate aberrant gene transcription in stress-associated mental disorders. However, it remains to be elucidated about the role of DNA methylation and its catalyzing enzymes, DNA methyltransferases (DNMTs), in this process. Here, we found that male rats exposed to chronic (2-week) unpredictable stress exhibited a substantial reduction of Dnmt3a after stress cessation in the prefrontal cortex (PFC), a key target region of stress. Treatment of unstressed control rats with DNMT inhibitors recapitulated the effect of chronic unpredictable stress on decreased AMPAR expression and function in PFC. In contrast, overexpression of Dnmt3a in PFC of stressed animals prevented the loss of glutamatergic responses. Moreover, the stress-induced behavioral abnormalities, including the impaired recognition memory, heightened aggression, and hyperlocomotion, were partially attenuated by Dnmt3a expression in PFC of stressed animals. Finally, we found that there were genome-wide DNA methylation changes and transcriptome alterations in PFC of stressed rats, both of which were enriched at several neural pathways, including glutamatergic synapse and microtubule-associated protein kinase signaling. These results have therefore recognized the potential role of DNA epigenetic modification in stress-induced disturbance of synaptic functions and cognitive and emotional processes.

Effects of early-life zinc deficiency on learning and memory in offspring and the changes in DNA methylation patterns

OBJECTIVE

To investigate the effect of maternal zinc deficiency on learning and memory in offspring and the changes in DNA methylation patterns.

METHODS

Pregnant rats were divided into zinc adequate (ZA), zinc deficient (ZD), and paired fed (PF) groups. Serum zinc contents and AKP activity in mother rats and offspring at P21 (end of lactation) and P60 (weaned, adult) were detected. Cognitive ability of offspring at P21 and P60 were determined by Morris water maze. The expression of proteins including DNMT3a, DNMT1, GADD45β, MeCP2 and BDNF in the offspring hippocampus were detected by Western-blot. The methylation status of BDNF promoter region in hippocampus of offspring rats was detected by MS-qPCR.

RESULTS

Compared with the ZA and PF groups, pups in the ZD group had lower zinc levels and AKP activity in the serum, spent more time finding the platform and spent less time going through the platform area. Protein expression of DNMT1 and GADD45b were downregulated in the ZD group during P0 and P21 but not P60 compared with the ZA and PF group, these results were consistent with a reduction in BDNF protein at P0 (neonate), P21. However, when pups of rats in the ZD group were supplemented with zinc ion from P21 to P60, MeCP2 and GADD45b expression were significantly downregulated compared with the ZA and PF group.

CONCLUSION

Post-weaning zinc supplementation may improve cognitive impairment induced by early life zinc deficiency, whereas it may not completely reverse the abnormal expression of particular genes that are involved in DNA methylation, binding to methylated DNA and neurogenesis.

DNA methylation: A mechanism for sustained alteration of KIR4.1 expression following central nervous system insult

Kir4.1, a glial-specific inwardly rectifying potassium channel, is implicated in astrocytic maintenance of K+ homeostasis. Underscoring the role of Kir4.1 in central nervous system (CNS) functioning, genetic mutations in KCNJ10, the gene which encodes Kir4.1, causes seizures, ataxia and developmental disability in humans. Kir4.1 protein and mRNA loss are consistently observed in CNS injury and neurological diseases linked to hyperexcitability and neuronal dysfunction, leading to the notion that Kir4.1 represents an attractive therapeutic target. Despite this, little is understood regarding the mechanisms that underpin this downregulation. Previous work by our lab revealed that DNA hypomethylation of the Kcnj10 gene functions to regulate mRNA levels during astrocyte maturation whereas hypermethylation in vitro led to decreased promoter activity. In the present study, we utilized two vastly different injury models with known acute and chronic loss of Kir4.1 protein and mRNA to evaluate the methylation status of Kcnj10 as a candidate molecular mechanism for reduced transcription and subsequent protein loss. Examining whole hippocampal tissue and isolated astrocytes, in a lithium-pilocarpine model of epilepsy, we consistently identified hypermethylation of CpG island two, which resides in the large intronic region spanning the Kcnj10 gene. Strikingly similar results were observed using the second injury paradigm, a fifth cervical (C5) vertebral hemi-contusion model of spinal cord injury. Our previous work indicates the same gene region is significantly hypomethylated when transcription increases during astrocyte maturation. Our results suggest that DNA methylation can bidirectionally modulate Kcnj10 transcription and may represent a targetable molecular mechanism for the restoring astroglial Kir4.1 expression following CNS insult.

Epigenetics, Development, and Psychopathology

Epigenetic mechanisms govern the transcription of the genome. Research with model systems reveals that environmental conditions can directly influence epigenetic mechanisms that are associated with interindividual differences in gene expression in brain and neural function. In this review, we provide a brief overview of epigenetic mechanisms and research with relevant rodent models. We emphasize more recent translational research programs in epigenetics as well as the challenges inherent in the integration of epigenetics into developmental and clinical psychology. Our objectives are to present an update with respect to the translational relevance of epigenetics for the study of psychopathology and to consider the state of current research with respect to its potential importance for clinical research and practice in mental health.

Integrated Epigenetics, Transcriptomics, and Metabolomics to Analyze the Mechanisms of Benzo[a]pyrene Neurotoxicity in the Hippocampus

Benzo[a]pyrene (B[a]P) is a common environmental pollutant that is neurotoxic to mammals, which can cause changes to hippocampal function and result in cognitive disorders. The mechanisms of B[a]P-induced impairments are complex .To date there have been no studies on the association of epigenetic, transcriptomic, and metabolomic changes with neurotoxicity after B[a]P exposure. In the present study, we investigated the global effect of B[a]P on DNA methylation patterns, noncoding RNAs (ncRNAs) expression, coding RNAs expression, and metabolites in the rat hippocampus. Male Sprague Dawley rats (SD rats) received daily gavage of B[a]P (2.0 mg/kg body weight [BW]) or corn oil for 7 weeks. Learning and memory ability was analyzed using the Morris water maze (MWM) test and change to cellular ultrastructure in the hippocampus was analyzed using electron microscope observation. Integrated analysis of epigenetics, transcriptomics, and metabolomics was conducted to investigate the effect of B[a]P exposure on the signaling and metabolic pathways. Our results suggest that B[a]P could lead to learning and memory deficits, likely as a result of epigenetic and transcriptomic changes that further affected the expression of CACNA1C, Tpo, etc. The changes in expression ultimately affecting LTP, tyrosine metabolism, and other important metabolic pathways.

Sex Differences in the Epigenome: A Cause or Consequence of Sexual Differentiation of the Brain?

Females and males display differences in neural activity patterns, behavioral responses, and incidence of psychiatric and neurological diseases. Sex differences in the brain appear throughout the animal kingdom and are largely a consequence of the physiological requirements necessary for the distinct roles of the two sexes in reproduction. As with the rest of the body, gonadal steroid hormones act to specify and regulate many of these differences. It is thought that transient hormonal signaling during brain development gives rise to persistent sex differences in gene expression via an epigenetic mechanism, leading to divergent neurodevelopmental trajectories that may underlie sex differences in disease susceptibility. However, few genes with a persistent sex difference in expression have been identified, and only a handful of studies have employed genome-wide approaches to assess sex differences in epigenomic modifications. To date, there are no confirmed examples of gene regulatory elements that direct sex differences in gene expression in the brain. Here, we review foundational studies in this field, describe transcriptional mechanisms that could act downstream of hormone receptors in the brain, and suggest future approaches for identification and validation of sex-typical gene programs. We propose that sexual differentiation of the brain involves self-perpetuating transcriptional states that canalize sex-specific development.

Understanding Epigenetics in the Neurodegeneration of Alzheimer's Disease: SAMP8 Mouse Model

Epigenetics is emerging as the missing link among genetic inheritance, environmental influences, and body and brain health status. In the brain, specific changes in nucleic acids or their associated proteins in neurons and glial cells might imprint differential patterns of gene activation that will favor either cognitive enhancement or cognitive loss for more than one generation. Furthermore, derangement of age-related epigenetic signaling is appearing as a significant risk factor for illnesses of aging, including neurodegeneration and Alzheimer’s disease (AD). In addition, better knowledge of epigenetic mechanisms might provide hints and clues in the triggering and progression of AD. Intense research in experimental models suggests that molecular interventions for modulating epigenetic mechanisms might have therapeutic applications to promote cognitive maintenance through an advanced age. The SAMP8 mouse is a senescence model with AD traits in which the study of epigenetic alterations may unveil epigenetic therapies against the AD.

Periconceptional maternal alcohol consumption leads to behavioural changes in adult and aged offspring and alters the expression of hippocampal genes associated with learning and memory and regulators of the epigenome

Maternal alcohol consumption throughout pregnancy can result in long term behavioural deficits in offspring. However, less is known about the impact of alcohol during the periconceptional period (PC). The aim of this study was to examine the effect of PC ethanol (PC:EtOH) exposure on long term cognitive function; including memory and anxiety. Rats were exposed to a liquid diet containing ethanol (EtOH) (12.5% vol;vol) or a control diet from 4 days prior to mating until day 4 of pregnancy. Separate cohorts of animals were tested at 6 months (adult) or 15-18 months of age (aged). Offspring underwent a series of behavioural tests to assess anxiety, spatial and recognition memory. The hippocampus was collected, and mRNA expression of epigenetic modifiers and genes implicated in learning and memory were examined. PC:EtOH exposure resulted in a subtle anxiety like behaviour in adult female offspring with a significant reduction in directed exploring/head dipping behaviour during holeboard testing. In aged male offspring, PC:EtOH exposure resulted in a tendency for increased directed exploring/head dipping behaviour during holeboard testing. No differences between treatments were observed in the elevated plus maze. Aged female offspring exposed to PC:EtOH demonstrated short term spatial memory impairment (P < 0.05). PC:EtOH resulted in an upregulation of hippocampal mRNA expression of bdnf, grin2a and grin2b at 18 months of age along with increased expression of epigenetic modifiers (dnmt1, dnmt3a and hdac2). In conclusion, PC:EtOH can lead to sex specific anxiety-like behaviour and impairments in spatial memory and altered hippocampal gene expression.

Corticosterone is correlated to mediators of neural plasticity and epigenetic potential in the hippocampus of Senegalese house sparrows (Passer domesticus)

Our previous research on range-expanding house sparrows in Kenya revealed that (i) range-edge birds released more corticosterone (CORT) in response to a stressor than range-core birds, ii) that range-edge birds were more exploratory than range-core birds, and that (iii) all birds exhibited extensive variation in genome-wide DNA methylation among individuals, regardless of their position along the range expansion. Within the hippocampus, mediators of neural plasticity such as brain-derived neurotrophic factor (BDNF), can influence and be influenced by CORT, hippocampus-associated behaviors and regulatory epigenetic modification enzymes. Here, we investigated whether individuals and populations colonizing a new geographic range, Senegal, vary in the expression of BDNF and DNA methyltransferases (DNMTs) within the hippocampus and the release of CORT in response to a stressor. DNMT expression is an important mediator of epigenetic potential, the propensity of a genome to capacitate phenotypic variation via mechanisms such as DNA methylation. We surveyed three populations across Senegal, predicting that hippocampal BDNF and DNMT expression would be highest at the range-edge, and that BDNF and DNMT would be inversely related to one another, but would each positively covary with CORT within individuals. We found a nonlinear relationship between CORT and BDNF expression within individuals. Moreover, we found that CORT positively covaried with DNMT1 expression in a more recently established population, while the reverse was true in the oldest population (i.e. at the range-core). Our study is among the first to explore whether and how variation in CORT regulation contributes to variation in mediators of neural plasticity and epigenetic potential within the hippocampus of a range-expanding vertebrate.

Genome-wide DNA methylation changes associated with olfactory learning and memory in Apis mellifera

The honeybee is a model organism for studying learning and memory formation and its underlying molecular mechanisms. While DNA methylation is well studied in caste differentiation, its role in learning and memory is not clear in honeybees. Here, we analyzed genome-wide DNA methylation changes during olfactory learning and memory process in A. mellifera using whole genome bisulfite sequencing (WGBS) method. A total of 853 significantly differentially methylated regions (DMRs) and 963 differentially methylated genes (DMGs) were identified. We discovered that 440 DMRs of 648 genes were hypermethylated and 274 DMRs of 336 genes were hypomethylated in trained group compared to untrained group. Of these DMGs, many are critical genes involved in learning and memory, such as Creb, GABA_BR and Ip3k, indicating extensive involvement of DNA methylation in honeybee olfactory learning and memory process. Furthermore, key enzymes for histone methylation, RNA editing and miRNA processing also showed methylation changes during this process, implying that DNA methylation can affect learning and memory of honeybees by regulating other epigenetic modification processes.

Mecp2 Mediates Experience-Dependent Transcriptional Upregulation of Ryanodine Receptor Type-3

Mecp2 is a DNA methylation reader that plays a critical role in experience-dependent plasticity. Increasing evidence supports a role for epigenetic modifications in activity-induced gene expression. Hence, candidate genes related to such phenomena are of great interest. Ryanodine receptors are intracellular calcium channels that contribute to hippocampal synaptic plasticity, dendritic spine remodeling, and participate in learning and memory processes. Here we exposed mice to the enriched environment (EE) paradigm, which through increased stimulation induces experience dependent-plasticity, to explore a role for methyl-cytosines, and Mecp2 in directing Ryanodine receptor 3 (Ryr3) transcriptional activity. EE induced a hippocampal-specific increase in the methylation of discrete cytosines located at a Ryr3 isoform promoter; chromatin immunoprecipitation experiments revealed that EE increased Mecp2 binding to this Ryr3 isoform promoter. Interestingly, the experimental paradigm induced robust Ryr3 upregulation, accompanied by miR132-dependent suppression of p250GAP, a pathway driving synaptogenesis. In contrast to WT mice, Mecp2-null mice showed diminished levels of Ryr3 and displayed impaired EE-induced Ryr3 upregulation, compromising miR132 dependent suppression of p250GAP and experience-dependent structural plasticity. Based on these results, we propose that Mecp2 acts as a transcriptional activator of Ryr3, contributing to experience-dependent plasticity.

Neuronal DNA Methyltransferases: Epigenetic Mediators between Synaptic Activity and Gene Expression?

DNMT3A and 3B are the main de novo DNA methyltransferases (DNMTs) in the brain that introduce new methylation marks to non-methylated DNA in postmitotic neurons. DNA methylation is a key epigenetic mark that is known to regulate important cellular processes in neuronal development and brain plasticity. Accumulating evidence disclosed rapid and dynamic changes in DNA methylation of plasticity-relevant genes that are important for learning and memory formation. To understand how DNMTs contribute to brain function and how they are regulated by neuronal activity is a prerequisite for a deeper appreciation of activity-dependent gene expression in health and disease. This review discusses the functional role of de novo methyltransferases and in particular DNMT3A1 in the adult brain with special emphasis on synaptic plasticity, memory formation, and brain disorders.

The chemistries and consequences of DNA and RNA methylation and demethylation

Chemical modification of nucleobases plays an important role for the control of gene expression on different levels. That includes the modulation of translation by modified tRNA-bases or silencing and reactivation of genes by methylation and demethylation of cytosine in promoter regions. Especially dynamic methylation of adenine and cytosine is essential for cells to adapt to their environment or for the development of complex organisms from a single cell. Errors in the cytosine methylation pattern are associated with most types of cancer and bacteria use methylated nucleobases to resist antibiotics. This Point of View wants to shed light on the known and potential chemistry of DNA and RNA methylation and demethylation. Understanding the chemistry of these processes on a molecular level is the first step towards a deeper knowledge about their regulation and function and will help us to find ways how nucleobase methylation can be manipulated to treat diseases.

Epigenetic determinants of space radiation-induced cognitive dysfunction

Among the dangers to astronauts engaging in deep space missions such as a Mars expedition is exposure to radiations that put them at risk for severe cognitive dysfunction. These radiation-induced cognitive impairments are accompanied by functional and structural changes including oxidative stress, neuroinflammation, and degradation of neuronal architecture. The molecular mechanisms that dictate CNS function are multifaceted and it is unclear how irradiation induces persistent alterations in the brain. Among those determinants of cognitive function are neuroepigenetic mechanisms that translate radiation responses into altered gene expression and cellular phenotype. In this study, we have demonstrated a correlation between epigenetic aberrations and adverse effects of space relevant irradiation on cognition. In cognitively impaired irradiated mice we observed increased 5-methylcytosine and 5-hydroxymethylcytosine levels in the hippocampus that coincided with increased levels of the DNA methylating enzymes DNMT3a, TET1 and TET3. By inhibiting methylation using 5-iodotubercidin, we demonstrated amelioration of the epigenetic effects of irradiation. In addition to protecting against those molecular effects of irradiation, 5-iodotubercidin restored behavioral performance to that of unirradiated animals. The findings of this study establish the possibility that neuroepigenetic mechanisms significantly contribute to the functional and structural changes that affect the irradiated brain and cognition.

Recent developments in the behavioural and pharmacological enhancement of extinction of drug seeking

One of the principal barriers to overcoming addiction is the propensity to relapse, even after months or years of abstinence. Relapse can be precipitated by cues and contexts associated with drug use; thus, decreasing the conditioned properties of these cues and contexts may assist in preventing relapse. The predictive power of drug cues and contexts can be reduced by repeatedly presenting them in the absence of the drug reinforcer, a process known as extinction. The potential of extinction to limit relapse has generated considerable interest and research over the past few decades. While pre-clinical animal models suggest extinction learning assists relapse prevention, treatment efficacy is often lacking when extinction learning principles are translated into clinical trials. Conklin and Tiffany (Addiction, 2002) suggest the lack of efficacy in clinical practice may be due to limited translation of procedures demonstrated through animal research and propose several methodological improvements to enhance extinction learning for drug addiction. This review will examine recent advances in the behavioural and pharmacological manipulation of extinction learning, based on research from pre-clinical models. In addition, the translation of pre-clinical findings-both those suggested by Conklin and Tiffany () and novel demonstrations from the past 13 years-into clinical trials and the efficacy of these methods in reducing craving and relapse, where available, will be discussed. Finally, we highlight areas where promising pre-clinical models have not yet been integrated into current clinical practice but, if applied, could improve upon existing behavioural and pharmacological methods.

Impact of DNMT1 and DNMT3a forebrain knockout on depressive- and anxiety like behavior in mice

DNA methylation has been shown to impact certain forms of synaptic and behavioral plasticity that have been implicated in the development in psychiatric disorders. DNA methylation is catalyzed by DNA methyltransferase (DNMT) enzymes that continue to be expressed in postmitotic neurons in the forebrain. Using a conditional forebrain knockout of DNMT1 or DNMT3a we assessed the role of these DNMTs in anxiety and depressive-like behavior in mice using an array of behavioral testing paradigms. Forebrain deletion of DNMT1 had anxiolytic and antidepressant-like properties as assessed by elevated plus maze, novelty suppressed feeding, forced swim, and social interaction tests. DNMT3a knockout mice, by contrast, did not exhibit significant behavioral alterations in these tests. Given the putative role of altered DNA methylation patterns in the development of schizophrenia, we also assessed DNMT1 and DNMT3a knockout mice in a prepulse inhibition task and found an enhanced prepulse inhibition of startle in DNMT1 knockouts relative to wild type mice, with no change evident in DNMT3a knockout mice. Our data suggest that DNMT1 and DNMT3a are distinctly involved in affective behavior and that DNMT1 may ultimately represent a potential target for treatment of certain affective behavioral disorders.

Effect of vitamin B12 and omega-3 fatty acid supplementation on brain neurotrophins and cognition in rats: A multigeneration study

Vitamin B12 and omega-3 fatty acids are important nutrients required for neuronal functioning. We have demonstrated the beneficial effects of vitamin B12 and omega-3 fatty acid supplementation on brain neurotrophins and cognition in the first and second generation offspring. However, there is a need to examine if the effects are sustained in the third generation offspring. This study reports the effects of vitamin B12 and omega-3 fatty acid supplementation across three consecutive generations on brain neurotrophins like brain derived neurotrophic factor (BDNF); nerve growth factor (NGF) and cognitive performance in the third generation male offspring. Three successive generations of Wistar rats were assigned the following groups throughout pregnancy, lactation and adulthood: i) Control, ii) vitamin B12 deficient (BD), iii) vitamin B12 deficient + omega-3 fatty acid (BDO), iv) vitamin B12 supplemented (BS) and v) vitamin B12 supplemented + omega-3 fatty acid (BSO). The BD group demonstrated lower (p < 0.01) NGF in the cortex but not BDNF levels although the cognition was impaired (p < 0.01). In contrast, in the BDO group, higher NGF levels were observed in the hippocampus and animals demonstrated improved (p < 0.01) cognitive performance. Vitamin B12 supplementation showed comparable BDNF levels in the hippocampus while their levels were lower in the cortex as compared to the control (p < 0.05). These animals showed more reference and working memory errors (p < 0.01) as compared to the control group. A combined supplementation of vitamin B12 and omega-3 fatty acid showed higher (p < 0.01) levels of DHA and NGF in the hippocampus, higher BDNF in both hippocampus and cortex and improved cognitive performance. Our findings have implications for fortification of foods with vitamin B12 and omega-3 fatty acids in improving brain development.

Possible Involvement of Standardized Bacopa monniera Extract (CDRI-08) in Epigenetic Regulation of reelin and Brain-Derived Neurotrophic Factor to Enhance Memory

Bacopa monniera extract (CDRI-08; BME) has been known to improve learning and memory, and understanding the molecular mechanisms may help to know its specificity. We investigated whether the BME treatment alters the methylation status of reelin and brain-derived neurotropic factor (BDNF) to enhance the memory through the interaction of N-methyl-D-aspartate receptor (NMDAR) with synaptic proteins. Rat pups were subjected to novel object recognition test following daily oral administration of BME (80 mg/kg) in 0.5% gum acacia (per-orally, p.o.; PND 15–29)/three doses of 5-azacytidine (5-azaC; 3.2 mg/kg) in 0.9% saline (intraperitoneally, i.p.) on PND-30. After the behavioral test, methylation status of reelin, BDNF and activation of NMDAR, and its interactions with synaptic proteins were tested. Rat pups treated with BME/5-azaC showed higher discrimination towards novel objects than with old objects during testing. Further, we observed an elevated level of unmethylated DNA in reelin and BDNF promoter region. Up-regulated reelin along with the splice variant of apolipoprotein E receptor 2 (ApoER 2, ex 19) form a cluster and activate NMDAR through disabled adopter protein-1 (DAB1) to enhance BDNF. Observed results suggest that BME regulate reelin epigenetically, which might enhance NMDAR interactions with synaptic proteins and induction of BDNF. These changes may be linked with improved novel object recognition memory.

Epigenetic basis of sensitization to stress, affective episodes, and stimulants: implications for illness progression and prevention

OBJECTIVES

The process of sensitization (increased responsivity) to the recurrence of stressors, affective episodes, and bouts of substance abuse that can drive illness progression in the recurrent affective disorders requires a memory of and increased reactivity to the prior exposures. A wealth of studies now supports the postulate that epigenetic mechanisms underlie both normal and pathological memory processes.

METHODS

We selectively reviewed the literature pertinent to the role of epigenetics in behavioral sensitization phenomena and discuss its clinical implications.

RESULTS

Epigenetics means above genetics and refers to environmental effects on the chemistry of DNA, histones (around which DNA is wound), and microRNA that change how easily genes are turned on and off. The evidence supports that sensitization to repeated stressor, affective episodes, and substance is likely based on epigenetic mechanisms and that these environmentally based processes can then become targets for prevention, early intervention, and ongoing treatment. Sensitization processes are remediable or preventable risk factors for a poor illness outcome and deserve increased clinical, public health, and research attention in the hopes of making the recurrent unipolar and bipolar affective disorders less impairing, disabling, and lethal by suicide and increased medical mortality.

CONCLUSIONS

The findings that epigenetic chemical marks, which change in the most fundamental way how genes are regulated, mediate the long-term increased responsivity to recurrent stressors, mood episodes, and bouts of substance abuse should help change how the affective disorders are conceptualized and move treatment toward earlier, more comprehensive, and sustained pharmacoprophylaxis.

Epigenetic Mechanisms in Developmental Alcohol-Induced Neurobehavioral Deficits

Alcohol consumption during pregnancy and its damaging consequences on the developing infant brain are significant public health, social, and economic issues. The major distinctive features of prenatal alcohol exposure in humans are cognitive and behavioral dysfunction due to damage to the central nervous system (CNS), which results in a continuum of disarray that is collectively called fetal alcohol spectrum disorder (FASD). Many rodent models have been developed to understand the mechanisms of and to reproduce the human FASD phenotypes. These animal FASD studies have provided several molecular pathways that are likely responsible for the neurobehavioral abnormalities that are associated with prenatal alcohol exposure of the developing CNS. Recently, many laboratories have identified several immediate, as well as long-lasting, epigenetic modifications of DNA methylation, DNA-associated histone proteins and microRNA (miRNA) biogenesis by using a variety of epigenetic approaches in rodent FASD models. Because DNA methylation patterns, DNA-associated histone protein modifications and miRNA-regulated gene expression are crucial for synaptic plasticity and learning and memory, they can therefore offer an answer to many of the neurobehavioral abnormalities that are found in FASD. In this review, we briefly discuss the current literature of DNA methylation, DNA-associated histone proteins modification and miRNA and review recent developments concerning epigenetic changes in FASD.

Genome Engineering with TALE and CRISPR Systems in Neuroscience

Recent advancement in genome engineering technology is changing the landscape of biological research and providing neuroscientists with an opportunity to develop new methodologies to ask critical research questions. This advancement is highlighted by the increased use of programmable DNA-binding agents (PDBAs) such as transcription activator-like effector (TALE) and RNA-guided clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated (Cas) systems. These PDBAs fused or co-expressed with various effector domains allow precise modification of genomic sequences and gene expression levels. These technologies mirror and extend beyond classic gene targeting methods contributing to the development of novel tools for basic and clinical neuroscience. In this Review, we discuss the recent development in genome engineering and potential applications of this technology in the field of neuroscience.

Epigenetic mechanisms in sexual differentiation of the brain and behaviour

Circumstantial evidence alone argues that the establishment and maintenance of sex differences in the brain depend on epigenetic modifications of chromatin structure. More direct evidence has recently been obtained from two types of studies: those manipulating a particular epigenetic mechanism, and those examining the genome-wide distribution of specific epigenetic marks. The manipulation of histone acetylation or DNA methylation disrupts the development of several neural sex differences in rodents. Taken together, however, the evidence suggests there is unlikely to be a simple formula for masculine or feminine development of the brain and behaviour; instead, underlying epigenetic mechanisms may vary by brain region or even by dependent variable within a region. Whole-genome studies related to sex differences in the brain have only very recently been reported, but suggest that males and females may use different combinations of epigenetic modifications to control gene expression, even in cases where gene expression does not differ between the sexes. Finally, recent findings are discussed that are likely to direct future studies on the role of epigenetic mechanisms in sexual differentiation of the brain and behaviour.

The lasting impact of early-life adversity on individuals and their descendants: potential mechanisms and hope for intervention

The adverse effects of early-life stress are pervasive, with well-established mental and physical health consequences for exposed individuals. The impact of early adverse experiences is also highly persistent, with documented increases in risk for mental illness across the life span that are accompanied by stable alterations in neural function and hormonal responses to stress. Here, we review some of these 'stress phenotypes', with a focus on intermediary factors that may signal risk for long-term mental health outcomes, such as altered development of the fear regulation system. Intriguingly, recent research suggests that such stress phenotypes may persist even beyond the life span of the individuals, with consequences for their offspring and grand-offspring. Phenotypic characteristics may be transmitted to future generations via either the matriline or the patriline, a phenomenon that has been demonstrated in both human and animal studies. In this review, we highlight behavioral and epigenetic factors that may contribute to this multigenerational transmission and discuss the potential of various treatment approaches that may halt the cycle of stress phenotypes.