Epigenetic control of sexual differentiation of the bed nucleus of the stria terminalis

Gonadal Hormone-Dependent Sexual Differentiation of a Female-Biased Sexually Dimorphic Cell Group in the Principal Nucleus of the Bed Nucleus of the Stria Terminalis in Mice

We recently reported a female-biased sexually dimorphic area in the mouse brain in the boundary region between the preoptic area and the bed nucleus of the stria terminalis (BNST). We reexamined this area and found that it is a ventral part of the principal nucleus of the BNST (BNSTp). The BNSTp is a male-biased sexually dimorphic nucleus, but the ventral part of the BNSTp (BNSTpv) exhibits female-biased sex differences in volume and neuron number. The volume and neuron number of the BNSTpv were increased in males by neonatal orchiectomy and decreased in females by treatment with testosterone, dihydrotestosterone, or estradiol within 5 days after birth. Sex differences in the volume and neuron number of the BNSTpv emerged before puberty. These sex differences became prominent in adulthood with increasing volume in females and loss of neurons in males during the pubertal/adolescent period. Prepubertal orchiectomy did not affect the BNSTpv, although prepubertal ovariectomy reduced the volume increase and induced loss of neurons in the female BNSTpv. In contrast, the volume and neuron number of male-biased sexually dimorphic nuclei that are composed of mainly calbindin neurons and are located in the preoptic area and BNST were decreased by prepubertal orchiectomy but not affected by prepubertal ovariectomy. Testicular testosterone during the postnatal period may defeminize the BNSTpv via binding directly to the androgen receptor and indirectly to the estrogen receptor after aromatization, although defeminization may proceed independently of testicular hormones in the pubertal/adolescent period. Ovarian hormones may act to feminize the BNSTpv during the pubertal/adolescent period.

Transgenerational effects of early environmental insults on aging and disease incidence

Adverse early life experiences are major influences on developmental trajectories with potentially life-long consequences. Prenatal or early postnatal exposure to stress, undernutrition or environmental toxicants may reprogram brain development and increase risk of behavioural and neurological disorders later in life. Not only experience within a single lifetime, but also ancestral experience affects health trajectories and chances of successful aging. The central mechanism in transgenerational programming of a disease may be the formation of epigenetic memory. This review explores transgenerational effects of early adverse experience on health and disease incidence in older age. First, we address mechanisms of developmental and transgenerational programming of disease and inheritance. Second, we discuss experimental and clinical findings linking early environmental determinants to adverse aging trajectories in association with possible parental contributions and sex-specific effects. Third, we outline the main mechanisms of age-related functional decline and suggest potential interventions to reverse negative effects of transgenerational programming. Thus, strategies that support healthy development and successful aging should take into account the potential influences of transgenerational inheritance.

Neuroimmunology and neuroepigenetics in the establishment of sex differences in the brain

The study of sex differences in the brain is a topic of neuroscientific study that has broad reaching implications for culture, society and biomedical science. Recent research in rodent models has led to dramatic shifts in our views of the mechanisms underlying the sexual differentiation of the brain. These include the surprising discoveries of a role for immune cells and inflammatory mediators in brain masculinization and a role for epigenetic suppression in brain feminization. How and to what degree these findings will translate to human brain development will be questions of central importance in future research in this field.

Understanding the epigenetic basis of sex differences in depression

Epigenetics refers to potentially heritable processes that can mediate both lasting and transient changes in gene expression in the absence of genome sequence alterations. The field of epigenetics has introduced a novel understanding of the mechanisms through which the environment can shape an individual and potentially its offspring. This Mini-Review examines the current literature exploring the role of epigenetics in the development of mood disorders such as depression. Depression is twofold more common in females, yet the majority of preclinical research has been conducted exclusively in male subjects. Here we discuss what is known about sex differences in epigenetic regulation and function and how this may contribute to the etiology and onset of mood disorders. © 2016 Wiley Periodicals, Inc.

Epigenetic impacts of endocrine disruptors in the brain

The acquisition of reproductive competence is organized and activated by steroid hormones acting upon the hypothalamus during critical windows of development. This review describes the potential role of epigenetic processes, particularly DNA methylation, in the regulation of sexual differentiation of the hypothalamus by hormones. We examine disruption of these processes by endocrine-disrupting chemicals (EDCs) in an age-, sex-, and region-specific manner, focusing on how perinatal EDCs act through epigenetic mechanisms to reprogram DNA methylation and sex steroid hormone receptor expression throughout life. These receptors are necessary for brain sexual differentiation and their altered expression may underlie disrupted reproductive physiology and behavior. Finally, we review the literature on histone modifications and non-coding RNA involvement in brain sexual differentiation and their perturbation by EDCs. By putting these data into a sex and developmental context we conclude that perinatal EDC exposure alters the developmental trajectory of reproductive neuroendocrine systems in a sex-specific manner.

Sex Differences in Nucleus Accumbens Transcriptome Profiles Associated with Susceptibility versus Resilience to Subchronic Variable Stress

Depression and anxiety disorders are more prevalent in females, but the majority of research in animal models, the first step in finding new treatments, has focused predominantly on males. Here we report that exposure to subchronic variable stress (SCVS) induces depression-associated behaviors in female mice, whereas males are resilient as they do not develop these behavioral abnormalities. In concert with these different behavioral responses, transcriptional analysis of nucleus accumbens (NAc), a major brain reward region, by use of RNA sequencing (RNA-seq) revealed markedly different patterns of stress regulation of gene expression between the sexes. Among the genes displaying sex differences was DNA methyltransferase 3a (Dnmt3a), which shows a greater induction in females after SCVS. Interestingly, Dnmt3a expression levels were increased in the NAc of depressed humans, an effect seen in both males and females. Local overexpression of Dnmt3a in NAc rendered male mice more susceptible to SCVS, whereas Dnmt3a knock-out in this region rendered females more resilient, directly implicating this gene in stress responses. Associated with this enhanced resilience of female mice upon NAc knock-out of Dnmt3a was a partial shift of the NAc female transcriptome toward the male pattern after SCVS. These data indicate that males and females undergo different patterns of transcriptional regulation in response to stress and that a DNA methyltransferase in NAc contributes to sex differences in stress vulnerability.

SIGNIFICANCE STATEMENT

Women have a higher incidence of depression than men. However, preclinical models, the first step in developing new diagnostics and therapeutics, have been performed mainly on male subjects. Using a stress-based animal model of depression that causes behavioral effects in females but not males, we demonstrate a sex-specific transcriptional profile in brain reward circuitry. This transcriptional profile can be altered by removal of an epigenetic mechanism, which normally suppresses DNA transcription, creating a hybrid male/female transcriptional pattern. Removal of this epigenetic mechanism also induces behavioral resilience to stress in females. These findings shed new light onto molecular factors controlling sex differences in stress response.

Hypothalamic control of the male neonatal testosterone surge

Sex differences in brain neuroanatomy and neurophysiology underpin considerable physiological and behavioural differences between females and males. Sexual differentiation of the brain is regulated by testosterone secreted by the testes predominantly during embryogenesis in humans and the neonatal period in rodents. Despite huge advances in understanding how testosterone, and its metabolite oestradiol, sexually differentiate the brain, little is known about the mechanism that actually generates the male-specific neonatal testosterone surge. This review examines the evidence for the role of the hypothalamus, and particularly the gonadotropin-releasing hormone (GnRH) neurons, in generating the neonatal testosterone surge in rodents and primates. Kisspeptin-GPR54 signalling is well established as a potent and critical regulator of GnRH neuron activity during puberty and adulthood, and we argue here for an equally important role at birth in driving the male-specific neonatal testosterone surge in rodents. The presence of a male-specific population of preoptic area kisspeptin neurons that appear transiently in the perinatal period provide one possible source of kisspeptin drive to neonatal GnRH neurons in the mouse.

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.

Cellular and molecular mechanisms of sexual differentiation in the mammalian nervous system

Neuroscientists are likely to discover new sex differences in the coming years, spurred by the National Institutes of Health initiative to include both sexes in preclinical studies. This review summarizes the current state of knowledge of the cellular and molecular mechanisms underlying sex differences in the mammalian nervous system, based primarily on work in rodents. Cellular mechanisms examined include neurogenesis, migration, the differentiation of neurochemical and morphological cell phenotype, and cell death. At the molecular level we discuss evolving roles for epigenetics, sex chromosome complement, the immune system, and newly identified cell signaling pathways. We review recent findings on the role of the environment, as well as genome-wide studies with some surprising results, causing us to re-think often-used models of sexual differentiation. We end by pointing to future directions, including an increased awareness of the important contributions of tissues outside of the nervous system to sexual differentiation of the brain.

EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals

The Endocrine Society's first Scientific Statement in 2009 provided a wake-up call to the scientific community about how environmental endocrine-disrupting chemicals (EDCs) affect health and disease. Five years later, a substantially larger body of literature has solidified our understanding of plausible mechanisms underlying EDC actions and how exposures in animals and humans-especially during development-may lay the foundations for disease later in life. At this point in history, we have much stronger knowledge about how EDCs alter gene-environment interactions via physiological, cellular, molecular, and epigenetic changes, thereby producing effects in exposed individuals as well as their descendants. Causal links between exposure and manifestation of disease are substantiated by experimental animal models and are consistent with correlative epidemiological data in humans. There are several caveats because differences in how experimental animal work is conducted can lead to difficulties in drawing broad conclusions, and we must continue to be cautious about inferring causality in humans. In this second Scientific Statement, we reviewed the literature on a subset of topics for which the translational evidence is strongest: 1) obesity and diabetes; 2) female reproduction; 3) male reproduction; 4) hormone-sensitive cancers in females; 5) prostate; 6) thyroid; and 7) neurodevelopment and neuroendocrine systems. Our inclusion criteria for studies were those conducted predominantly in the past 5 years deemed to be of high quality based on appropriate negative and positive control groups or populations, adequate sample size and experimental design, and mammalian animal studies with exposure levels in a range that was relevant to humans. We also focused on studies using the developmental origins of health and disease model. No report was excluded based on a positive or negative effect of the EDC exposure. The bulk of the results across the board strengthen the evidence for endocrine health-related actions of EDCs. Based on this much more complete understanding of the endocrine principles by which EDCs act, including nonmonotonic dose-responses, low-dose effects, and developmental vulnerability, these findings can be much better translated to human health. Armed with this information, researchers, physicians, and other healthcare providers can guide regulators and policymakers as they make responsible decisions.

Surprising origins of sex differences in the brain

This article is part of a Special Issue "SBN 2014". Discerning the biologic origins of neuroanatomical sex differences has been of interest since they were first reported in the late 60's and early 70's. The centrality of gonadal hormone exposure during a developmental critical window cannot be denied but hormones are indirect agents of change, acting to induce gene transcription or modulate membrane bound signaling cascades. Sex differences in the brain include regional volume differences due to differential cell death, neuronal and glial genesis, dendritic branching and synaptic patterning. Early emphasis on mechanism therefore focused on neurotransmitters and neural growth factors, but by and large these endpoints failed to explain the origins of neural sex differences. More recently evidence has accumulated in favor of inflammatory mediators and immune cells as principle regulators of brain sexual differentiation and reveal that the establishment of dimorphic circuits is not cell autonomous but instead requires extensive cell-to-cell communication including cells of non-neuronal origin. Despite the multiplicity of cells involved the nature of the sex differences in the neuroanatomical endpoints suggests canalization, a process that explains the robustness of individuals in the face of intrinsic and extrinsic variability. We propose that some neuroanatomical endpoints are canalized to enhance sex differences in the brain by reducing variability within one sex while also preventing the sexes from diverging too greatly. We further propose mechanisms by which such canalization could occur and discuss what relevance this may have to sex differences in behavior.

At the frontier of epigenetics of brain sex differences

The notion that epigenetics may play an important role in the establishment and maintenance of sex differences in the brain has garnered great enthusiasm but the reality in terms of actual advances has been slow. Two general approaches include the comparison of a particular epigenetic mark in males vs. females and the inhibition of key epigenetic enzymes or co-factors to determine if this eliminates a particular sex difference in brain or behavior. The majority of emphasis has been on candidate genes such as steroid receptors. Only recently have more generalized survey type approaches been achieved and these promise to open new vistas and accelerate discovery of important roles for DNA methylation, histone modification, genomic imprinting and microRNAs (miRs). Technical challenges abound and, while not unique to this field, will require novel thinking and new approaches by behavioral neuroendocrinologists.

Bisphenol A Interaction With Brain Development and Functions

Brain development is an organized, but constantly adaptive, process in which genetic and epigenetic signals allow neurons to differentiate, to migrate, and to develop correct connections. Gender specific prenatal sex hormone milieu participates in the dimorphic development of many neuronal networks. Environmental cues may interfere with these developmental programs, producing adverse outcomes. Bisphenol A (BPA), an estrogenic/antiandrogenic endocrine disruptor widely diffused in the environment, produces adverse effects at levels below the acceptable daily intake. This review analyzes the recent literature on the consequences of perinatal exposure to BPA environmental doses on the development of a dimorphic brain. The BPA interference with the development and function of the neuroendocrine hypothalamus and of the nuclei controlling energy balance, and with the hippocampal memory processing is also discussed. The detrimental action of BPA appears complex, involving different hormonal and epigenetic pathways activated, often in a dimorphic way, within clearcut susceptibility windows. To date, discrepancies in experimental approaches and in related outcomes make unfeasible to translate the available information into clear dose-response models for human risk assessment. Evaluation of BPA brain levels in relation to the appearance of adverse effects in future basic studies will certainly give better definition of the warning threshold for human health.

Evidence of a sex-dependent restrictive epigenome in schizophrenia

When compared to women, men have a higher incidence of schizophrenia, with increases in negative and cognitive symptoms, and an overall poorer disease course. Schizophrenia is conceptualized as a disorder of aberrant gene transcription and regulation. Thus, epigenetics, the study of environmentally induced changes in gene regulation, could advance our understanding of the molecular underpinnings of schizophrenia. Peripheral histone methyltransferase (HMT) mRNA levels have been previously shown to be significantly increased in patients with schizophrenia and correlate with symptomology. In this independent study, peripheral lymphocytes were extracted and clinical symptoms were measured on 74 participants, (40 patients with schizophrenia (19 women, 21 men) and 34 healthy individuals (19 women, 15 men)). HMT (G9α, SETDB1 and GLP) mRNA levels and their resulting histone modification H3K9me2 were measured with RT-PCR and ELISA respectively. Plasma estradiol levels were also measured via ELISA and correlated with HMT mRNA. Clinical symptoms were measured utilizing the Positive and Negative Syndrome Scale (PANSS) and the Heinrichs Carpenter Quality of Life Scale (QLS). The results indicate that men with schizophrenia expressed the highest levels of G9α, SETDB1 mRNA and H3K9me2 protein levels. Additionally, higher levels of symptom presentation and an overall poorer quality of life were correlated with higher HMT mRNA and H3K9me2 protein levels in a sex-dependent pattern. These data support the hypothesis of a sex-dependent restrictive epigenome contributing towards the etiology of schizophrenia. The histone methyltransferases measured here could be potential future therapeutic targets for small molecule pharmacology.

Epigenetic and transgenerational reprogramming of brain development

Neurodevelopmental programming - the implementation of the genetic and epigenetic blueprints that guide and coordinate normal brain development - requires tight regulation of transcriptional processes. During prenatal and postnatal time periods, epigenetic processes fine-tune neurodevelopment towards an end product that determines how an organism interacts with and responds to exposures and experiences throughout life. Epigenetic processes also have the ability to reprogramme the epigenome in response to environmental challenges, such as maternal stress, making the organism more or less adaptive depending on the future challenges presented. Epigenetic marks generated within germ cells as a result of environmental influences throughout life can also shape future generations long before conception occurs.

Age- and Sex-Dependent Changes in Androgen Receptor Expression in the Developing Mouse Cortex and Hippocampus

During the perinatal period, male mice are exposed to higher levels of testosterone (T) than females, which promotes sexual dimorphism in their brain structures and behaviors. In addition to acting via estrogen receptors after being locally converted into estradiol by aromatase, T also acts directly through androgen receptor (AR) in the brain. Therefore, we hypothesized that AR expression in the developing mouse cortex and hippocampus was sexually dimorphic. To test our hypothesis, we measured and determined AR mRNA and protein levels in mouse cortex/hippocampus collected on the day of birth (PN0) and 7 (PN7), 14 (PN14), and 21 (PN21) days after birth. We demonstrated that, as age advanced, AR mRNA levels increased in the cortex/hippocampus of both sexes but showed no sex difference. Two AR proteins, the full-length (110 kDa) and a smaller isoform (70 kDa), were detected in the developing mouse cortex/hippocampus with an age-dependent increase in protein levels of both AR isoforms at PN21 and a transient masculine increase in expression of the full-length AR protein on PN7. Thus, we conclude that the postnatal age and sex differences in AR protein expression in combination with the sex differences in circulating T may cause sexual differentiation of the mouse cortex/hippocampus.

Sex differences in mood disorders: perspectives from humans and rodent models

Mood disorders are devastating, often chronic illnesses characterized by low mood, poor affect, and anhedonia. Notably, mood disorders are approximately twice as prevalent in women compared to men. If sex differences in mood are due to underlying biological sex differences, a better understanding of the biology is warranted to develop better treatment or even prevention of these debilitating disorders. In this review, our goals are to: 1) summarize the literature related to mood disorders with respect to sex differences in prevalence, 2) introduce the corticolimbic brain network of mood regulation, 3) discuss strategies and challenges of modeling mood disorders in mice, 4) discuss mechanisms underlying sex differences and how these can be tested in mice, and 5) discuss how our group and others have used a translational approach to investigate mechanisms underlying sex differences in mood disorders in humans and mice.

Using sex differences in the developing brain to identify nodes of influence for seizure susceptibility and epileptogenesis

Sexual differentiation of the developing brain organizes the neural architecture differently between males and females, and the main influence on this process is exposure to gonadal steroids during sensitive periods of prenatal and early postnatal development. Many molecular and cellular processes are influenced by steroid hormones in the developing brain, including gene expression, cell birth and death, neurite outgrowth and synaptogenesis, and synaptic activity. Perturbations in these processes can alter neuronal excitability and circuit activity, leading to increased seizure susceptibility and the promotion of pathological processes that constitute epileptogenesis. In this review, we will provide a general overview of sex differences in the early developing brain that may be relevant for altered seizure susceptibility in early life, focusing on limbic areas of the brain. Sex differences that have the potential to alter the progress of epileptogenesis are evident at molecular and cellular levels in the developing brain, and include differences in neuronal excitability, response to environmental insult, and epigenetic control of gene expression. Knowing how these processes differ between the sexes can help us understand fundamental mechanisms underlying gender differences in seizure susceptibility and epileptogenesis.

Implications of prenatal steroid perturbations for neurodevelopment, behavior, and autism

The prenatal brain develops under the influence of an ever-changing hormonal milieu that includes endogenous fetal gonadal and adrenal hormones, placental and maternal hormones, and exogenous substances with hormonal activity that can cross the placental barrier. This review discusses the influences of endogenous fetal and maternal hormones on normal brain development and potential consequences of pathophysiological hormonal perturbations to the developing brain, with particular reference to autism. We also consider the effects of hormonal pharmaceuticals used for assisted reproduction, the maintenance of pregnancy, the prevention of congenital adrenal hypertrophy, and hormonal contraceptives continued into an unanticipated pregnancy, among others. These treatments, although in some instances life-saving, may have unintended consequences on the developing fetuses. Additional concern is raised by fetal exposures to endocrine-disrupting chemicals encountered universally by pregnant women from food/water containers, contaminated food, household chemicals, and other sources. What are the potential outcomes of prenatal steroid perturbations on neurodevelopmental and behavioral disorders, including autism-spectrum disorders? Our purposes here are 1) to summarize some consequences of steroid exposures during pregnancy for the development of brain and behavior in the offspring; 2) to summarize what is known about the relationships between exposures and behavior, including autism spectrum disorders; 3) to discuss the molecular underpinnings of such effects, especially molecular epigenetic mechanisms of prenatal steroid manipulations, a field that may explain effects of direct exposures, and even transgenerational effects; and 4) for all of these, to add cautionary notes about their interpretation in the name of scientific rigor.

Epigenetic changes in the estrogen receptor α gene promoter: implications in sociosexual behaviors

Estrogen action through estrogen receptor α (ERα) is involved in the control of sexual and social behaviors in adult mammals. Alteration of ERα gene activity mediated by epigenetic mechanisms, such as histone modifications and DNA methylation, in particular brain areas appears to be crucial for determining the extents of these behaviors between the sexes and among individuals within the same sex. This review provides a summary of the epigenetic changes in the ERα gene promoter that correlate with sociosexual behaviors.

Epigenetic regulation of estrogen-dependent memory

Hippocampal memory formation is highly regulated by post-translational histone modifications and DNA methylation. Accordingly, these epigenetic processes play a major role in the effects of modulatory factors, such as sex steroid hormones, on hippocampal memory. Our laboratory recently demonstrated that the ability of the potent estrogen 17β-estradiol (E2) to enhance hippocampal-dependent novel object recognition memory in ovariectomized female mice requires ERK-dependent histone H3 acetylation and DNA methylation in the dorsal hippocampus. Although these data provide valuable insight into the chromatin modifications that mediate the memory-enhancing effects of E2, epigenetic regulation of gene expression is enormously complex. Therefore, more research is needed to fully understand how E2 and other hormones employ epigenetic alterations to shape behavior. This review discusses the epigenetic alterations shown thus far to regulate hippocampal memory, briefly reviews the effects of E2 on hippocampal function, and describes in detail our work on epigenetic regulation of estrogenic memory enhancement.

Regulation of object recognition and object placement by ovarian sex steroid hormones

The ovarian hormones 17β-estradiol (E2) and progesterone (P4) are potent modulators of hippocampal memory formation. Both hormones have been demonstrated to enhance hippocampal memory by regulating the cellular and molecular mechanisms thought to underlie memory formation. Behavioral neuroendocrinologists have increasingly used the object recognition and object placement (object location) tasks to investigate the role of E2 and P4 in regulating hippocampal memory formation in rodents. These one-trial learning tasks are ideal for studying acute effects of hormone treatments on different phases of memory because they can be administered during acquisition (pre-training), consolidation (post-training), or retrieval (pre-testing). This review synthesizes the rodent literature testing the effects of E2 and P4 on object recognition (OR) and object placement (OP), and the molecular mechanisms in the hippocampus supporting memory formation in these tasks. Some general trends emerge from the data. Among gonadally intact females, object memory tends to be best when E2 and P4 levels are elevated during the estrous cycle, pregnancy, and in middle age. In ovariectomized females, E2 given before or immediately after testing generally enhances OR and OP in young and middle-aged rats and mice, although effects are mixed in aged rodents. Effects of E2 treatment on OR and OP memory consolidation can be mediated by both classical estrogen receptors (ERα and ERβ), and depend on glutamate receptors (NMDA, mGluR1) and activation of numerous cell signaling cascades (e.g., ERK, PI3K/Akt, mTOR) and epigenetic processes (e.g., histone acetylation, DNA methylation). Acute P4 treatment given immediately after training also enhances OR and OP in young and middle-aged ovariectomized females by activating similar cell signaling pathways as E2 (e.g., ERK, mTOR). The few studies that have administered both hormones in combination suggest that treatment can enhance OR and OP, but that effects are highly dependent on factors such as dose and timing of administration. In addition to providing more detail on these general conclusions, this review will discuss directions for future avenues of research into the hormonal regulation of object memory.

Epigenetics and sex differences in the brain: A genome-wide comparison of histone-3 lysine-4 trimethylation (H3K4me3) in male and female mice

Many neurological and psychiatric disorders exhibit gender disparities, and sex differences in the brain likely explain some of these effects. Recent work in rodents points to a role for epigenetics in the development or maintenance of neural sex differences, although genome-wide studies have so far been lacking. Here we review the existing literature on epigenetics and brain sexual differentiation and present preliminary analyses on the genome-wide distribution of histone-3 lysine-4 trimethylation in a sexually dimorphic brain region in male and female mice. H3K4me3 is a histone mark primarily organized as 'peaks' surrounding the transcription start site of active genes. We microdissected the bed nucleus of the stria terminalis and preoptic area (BNST/POA) in adult male and female mice and used ChIP-Seq to compare the distribution of H3K4me3 throughout the genome. We found 248 genes and loci with a significant sex difference in H3K4me3. Of these, the majority (71%) had larger H3K4me3 peaks in females. Comparisons with existing databases indicate that genes and loci with increased H3K4me3 in females are associated with synaptic function and with expression atlases from related brain areas. Based on RT-PCR, only a minority of genes with a sex difference in H3K4me3 has detectable sex differences in expression at baseline conditions. Together with previous findings, our data suggest that there may be sex biases in the use of epigenetic marks. Such biases could underlie sex differences in vulnerabilities to drugs or diseases that disrupt specific epigenetic processes.

Effects of Prenatal Testosterone Exposure on Sexually Dimorphic Gene Expression in the Neonatal Mouse Cortex and Hippocampus

OBJECTIVE

Using gene expression microarrays and reverse transcription with quantitative polymerase chain reaction (RT-qPCR), we have recently identified several novel genes that are differentially expressed in the neonatal male versus female mouse cortex/hippocampus (Armoskus et al.). Since perinatal testosterone (T) secreted by the developing testes masculinizes cortical and hippocampal structures and the behaviors regulated by these brain regions, we hypothesized that sexually dimorphic expression of specific selected genes in these areas might be regulated by T during early development.

METHODS

To test our hypothesis, we treated timed pregnant female mice daily with vehicle or testosterone propionate (TP) starting on embryonic day 16 until the day of birth. The cortex/hippocampus was collected from vehicle- and TP-treated, male and female neonatal pups. Total RNA was extracted from these brain tissues, followed by RT-qPCR to measure relative mRNA levels of seven sex chromosome genes and three autosomal genes that have previously showed sex differences.

RESULTS

The effect of prenatal TP was confirmed as it stimulated Dhcr24 expression in the neonatal mouse cortex/hippocampus and increased the anogenital distance in females. We found a significant effect of sex, but not TP, on expression of three Y-linked (Ddx3y, Eif2s3y, and Kdm5d), four X-linked (Eif2s3x, Kdm6a, Mid1, and Xist), and one autosomal (Klk8) genes in the neonatal mouse cortex/hippocampus.

CONCLUSION

Although most of the selected genes are not directly regulated by prenatal T, their sexually dimorphic expression might play an important role in the control of sexually differentiated cognitive and social behaviors as well as in the etiology of sex-biased neurological disorders and mental illnesses.

Sex, epilepsy, and epigenetics

Epilepsy refers to a heterogeneous group of disorders that are associated with a wide range of pathogenic mechanisms, seizure manifestations, comorbidity profiles, and therapeutic responses. These characteristics are all influenced quite significantly by sex. As with other conditions exhibiting such patterns, sex differences in epilepsy are thought to arise-at the most fundamental level-from the "organizational" and "activational" effects of sex hormones as well as from the direct actions of the sex chromosomes. However, our understanding of the specific molecular, cellular, and network level processes responsible for mediating sex differences in epilepsy remains limited. Because increasing evidence suggests that epigenetic mechanisms are involved both in epilepsy and in brain sexual dimorphism, we make the case here that analyzing epigenetic regulation will provide novel insights into the basis for sex differences in epilepsy.

Epigenetic mechanisms in pubertal brain maturation

Puberty is a critical period of development during which the reemergence of gonadotropin-releasing hormone secretion from the hypothalamus triggers a cascade of hormone-dependent processes. Maturation of specific brain regions including the prefrontal cortex occurs during this window, but the complex mechanisms underlying these dynamic changes are not well understood. Particularly, the potential involvement of epigenetics in this programming has been under-examined. The epigenome is known to guide earlier stages of development, and it is similarly poised to regulate vital pubertal-driven brain maturation. Further, as epigenetic machinery is highly environmentally responsive, its involvement may also lend this period of growth to greater vulnerability to external insults, resulting in reprogramming and increased disease risk. Importantly, neuropsychiatric diseases commonly present in individuals during or immediately following puberty, and environmental perturbations including stress may precipitate disease onset by disrupting the normal trajectory of pubertal brain development via epigenetic mechanisms. In this review, we discuss epigenetic processes involved in pubertal brain maturation, the potential points of derailment, and the importance of future studies for understanding this dynamic developmental window and gaining a better understanding of neuropsychiatric disease risk.

Administration of histone deacetylase inhibitor during neonatal period changes emotionality of adult male 129Sv mice

Environmental factors acting during the neonatal period affected the formation of phenotype of adult animals via epigenetic modifications of the genome, e.g. histone acetylation. We studied the effects of blockage of histone deacetylases with sodium valproate on week 1 of life on the behavioral pattern of adult male 129Sv mice. The results of behavioral tests attest to long-term changes in emotional, but not cognitive pattern of adult animals after sodium valproate administration, which manifested in increased anxiety of animals.

Epigenetic effect of testosterone in the behavior of C. elegans. A clue to explain androgen-dependent autistic traits?

Current research indicates that the causes of autism spectrum disorders (ASDs) are multifactorial and include both genetic and environmental factors. To date, several works have associated ASDs with mutations in genes that encode proteins involved in neuronal synapses; however other factors and the way they can interact with the development of the nervous system remain largely unknown. Some studies have established a direct relationship between risk for ASDs and the exposure of the fetus to high testosterone levels during the prenatal stage. In this work, in order to explain possible mechanisms by which this androgenic hormone may interact with the nervous system, C. elegans was used as an experimental model. We observed that testosterone was able to alter the behavioral pattern of the worm, including the gentle touch response and the pharyngeal pumping rate. This impairment of the behavior was abolished using specific RNAi against genes orthologous to the human androgen receptor gene. The effect of testosterone was eliminated in the nhr-69 (ok1926) deficient mutant, a putative ortholog of human AR gene, suggesting that this gene encodes a receptor able to interact with the hormone. On the other hand the testosterone effect remained in the gentle touch response during four generations in the absence of the hormone, indicating that some epigenetic mechanisms could be involved. Sodium butyrate, a histone deacetylase inhibitor, was able to abolish the effect of testosterone. In addition, the lasting effect of testosterone was eliminated after the dauer stage. These results suggest that testosterone may impair the nervous system function generating transgenerational epigenetic marks in the genome. This work may provide new paradigms for understanding biological mechanisms involved in ASDs traits.

Sex-specific Esr2 mRNA expression in the rat hypothalamus and amygdala is altered by neonatal bisphenol A exposure

Perinatal life is a critical window for sexually dimorphic brain organization, and profoundly influenced by steroid hormones. Exposure to endocrine-disrupting compounds may disrupt this process, resulting in compromised reproductive physiology and behavior. To test the hypothesis that neonatal bisphenol A (BPA) exposure can alter sex-specific postnatal Esr2 (Erβ) expression in brain regions fundamental to sociosexual behavior, we mapped Esr2 mRNA levels in the principal nucleus of the bed nucleus of the stria terminalis (BNSTp), paraventricular nucleus (PVN), anterior portion of the medial amygdaloid nucleus (MeA), super optic nucleus, suprachiasmatic nucleus, and lateral habenula across postnatal days (PNDs) 0-19. Next, rat pups of both sexes were subcutaneously injected with 10 μg estradiol benzoate (EB), 50 μg/kg BPA (LBPA), or 50 mg/kg BPA (HBPA) over the first 3 days of life and Esr2 levels were quantified in each region of interest (ROI) on PNDs 4 and 10. EB exposure decreased Esr2 signal in most female ROIs and in the male PVN. In the BNSTp, Esr2 expression decreased in LBPA males and HBPA females on PND 10, thereby reversing the sex difference in expression. In the PVN, Esr2 mRNA levels were elevated in LBPA females, also resulting in a reversal of sexually dimorphic expression. In the MeA, BPA decreased Esr2 expression on PND 4. Collectively, these data demonstrate that region- and sex-specific Esr2 expression is vulnerable to neonatal BPA exposure in regions of the developing brain critical to sociosexual behavior in rat.

Sexually selected traits: a fundamental framework for studies on behavioral epigenetics

Emerging evidence suggests that epigenetic-based mechanisms contribute to various aspects of sex differences in brain and behavior. The major obstacle in establishing and fully understanding this linkage is identifying the traits that are most susceptible to epigenetic modification. We have proposed that sexual selection provides a conceptual framework for identifying such traits. These are traits involved in intrasexual competition for mates and intersexual choice of mating partners and generally entail a combination of male-male competition and female choice. These behaviors are programmed during early embryonic and postnatal development, particularly during the transition from the juvenile to adult periods, by exposure of the brain to steroid hormones, including estradiol and testosterone. We evaluate the evidence that endocrine-disrupting compounds, including bisphenol A, can interfere with the vital epigenetic and gene expression pathways and with the elaboration of sexually selected traits with epigenetic mechanisms presumably governing the expression of these traits. Finally, we review the evidence to suggest that these steroid hormones can induce a variety of epigenetic changes in the brain, including the extent of DNA methylation, histone protein alterations, and even alterations of noncoding RNA, and that many of the changes differ between males and females. Although much previous attention has focused on primary sex differences in reproductive behaviors, such as male mounting and female lordosis, we outline why secondary sex differences related to competition and mate choice might also trace their origins back to steroid-induced epigenetic programming in disparate regions of the brain.

Sex differences in stress-induced social withdrawal: role of brain derived neurotrophic factor in the bed nucleus of the stria terminalis

Depression and anxiety disorders are more common in women than men, and little is known about the neurobiological mechanisms that contribute to this disparity. Recent data suggest that stress-induced changes in neurotrophins have opposing effects on behavior by acting in different brain networks. Social defeat has been an important approach for understanding neurotrophin action, but low female aggression levels in rats and mice have limited the application of these methods primarily to males. We examined the effects of social defeat in monogamous California mice (Peromyscus californicus), a species in which both males and females defend territories. We demonstrate that defeat stress increases mature brain-derived neurotrophic factor (BDNF) protein but not mRNA in the bed nucleus of the stria terminalis (BNST) in females but not males. Changes in BDNF protein were limited to anterior subregions of the BNST, and there were no changes in the adjacent nucleus accumbens (NAc). The effects of defeat on social withdrawal behavior and BDNF were reversed by chronic, low doses of the antidepressant sertraline. However, higher doses of sertraline restored social withdrawal and elevated BDNF levels. Acute treatment with a low dose of sertraline failed to reverse the effects of defeat. Infusions of the selective tyrosine-related kinase B receptor (TrkB) antagonist ANA-12 into the anterior BNST specifically increased social interaction in stressed females but had no effect on behavior in females naïve to defeat. These results suggest that stress-induced increases in BDNF in the anterior BNST contribute to the exaggerated social withdrawal phenotype observed in females.

Sex differences in anxiety and depression: role of testosterone

Compelling evidence exists for pervasive sex differences in pathological conditions, including anxiety and depressive disorders, with females more than twice as likely to be afflicted. Gonadal hormones may be a major factor in this disparity, given that women are more likely to experience mood disturbances during times of hormonal flux, and testosterone may have protective benefits against anxiety and depression. In this review we focus on the effects of testosterone in males and females, revealed in both human and animal studies. We also present possible neurobiological mechanisms underlying testosterone's mostly protective benefits, including the brain regions, neural circuits, and cellular and molecular pathways involved. While the precise underlying mechanisms remain unclear, both activational and organizational effects of testosterone appear to contribute to these effects. Future clinical studies are necessary in order to better understand when and how testosterone therapy may be effective in both sexes.

The biological basis of human sexual orientation: is there a role for epigenetics?

Sexual orientation is one of the largest sex differences in humans. The vast majority of the population is heterosexual, that is, they are attracted to members of the opposite sex. However, a small but significant proportion of people are bisexual or homosexual and experience attraction to members of the same sex. The origins of the phenomenon have long been the subject of scientific study. In this chapter, we will review the evidence that sexual orientation has biological underpinnings and consider the involvement of epigenetic mechanisms. We will first discuss studies that show that sexual orientation has a genetic component. These studies show that sexual orientation is more concordant in monozygotic twins than in dizygotic ones and that male sexual orientation is linked to several regions of the genome. We will then highlight findings that suggest a link between sexual orientation and epigenetic mechanisms. In particular, we will consider the case of women with congenital adrenal hyperplasia (CAH). These women were exposed to high levels of testosterone in utero and have much higher rates of nonheterosexual orientation compared to non-CAH women. Studies in animal models strongly suggest that the long-term effects of hormonal exposure (such as those experienced by CAH women) are mediated by epigenetic mechanisms. We conclude by describing a hypothetical framework that unifies genetic and epigenetic explanations of sexual orientation and the continued challenges facing sexual orientation research.

Epigenetic mechanisms may underlie the aetiology of sex differences in mental health risk and resilience

In this review, we propose that experiential and hormonal influences on biological sex during development may produce differences in the epigenome, and that these differences play an important role in gating risk or resilience to a number of neurological and psychiatric disorders. One intriguing hypothesis is that the framework belying sex differences in the brain creates differences in methylation and demethylation patterns, and these in turn confer risk and resilience to mental health disorders. Here, we discuss these concepts with regard to social behaviour in rodent models and briefly discuss their possible relevance to human disease.

Epigenetic contributions to hormonally-mediated sexual differentiation of the brain

It has been long established that hormones exert enduring influences on the developing brain that direct the reproductive response in adulthood, although the cellular mechanisms by which organisational effects are maintained have not been determined satisfactorily. Recent interest in epigenetic modifications to the nervous system has highlighted the potential for hormone-induced changes to the genome that could endure for the lifespan but not be transmitted to the next generation. Preliminary evidence suggests that this is indeed possible because sex differences in the histone code and in the methylation of CpGs in the promoters of specific genes have been identified and, at times, functionally correlated with behaviour. The present review provides an overview of epigenetic processes and discusses the current state-of-the-art, and also identifies future directions.

Epigenetics, oestradiol and hippocampal memory consolidation

Epigenetic alterations of histone proteins and DNA are essential for hippocampal synaptic plasticity and cognitive function, and contribute to the aetiology of psychiatric disorders and neurodegenerative diseases. Hippocampal memory formation depends on histone alterations and DNA methylation, and increasing evidence suggests that the regulation of these epigenetic processes by modulatory factors, such as environmental enrichment, stress and hormones, substantially influences memory function. Recent work from our laboratory suggests that the ability of the sex-steroid hormone 17β-oestradiol (E2 ) to enhance novel object recognition memory consolidation in young adult female mice is dependent on histone H3 acetylation and DNA methylation in the dorsal hippocampus. Our data also suggest that enzymes mediating DNA methylation and histone acetylation work in concert to regulate the effects of E2 on memory consolidation. These findings shed light on the epigenetic mechanisms that influence hormonal modulation of cognitive function, and may have important implications for understanding how hormones influence cognition in adulthood and ageing. The present review provides a brief overview of the literature on epigenetics and memory, describes in detail our findings demonstrating that epigenetic alterations regulate E2 -induced memory enhancement in female mice, and discusses future directions for research on the epigenetic regulation of E2 -induced memory enhancement.

Permanent and plastic epigenesis in neuroendocrine systems

The emerging area of neuroepigenetics has been linked to numerous mental health illnesses. Importantly, a large portion of what we know about early gene×environment interactions comes from examining epigenetic modifications of neuroendocrine systems. This review will highlight how neuroepigenetic mechanisms during brain development program lasting differences in neuroendocrine systems and how other neuroepigenetic processes remain plastic, even within the adult brain. As epigenetic mechanisms can either be stable or plastic, elucidating the mechanisms involved in reversing these processes could aid in understanding how to reverse pathological epigenetic programming.

Emerging concepts on the epigenetic and transcriptional regulation of the Kiss1 gene

Kisspeptin and its receptor have been implicated as critical regulators of reproductive physiology, with humans and mice without functioning kisspeptin systems displaying severe pubertal and reproductive defects. Alterations in the expression of Kiss1 (the gene encoding kisspeptin) over development, along with differences in Kiss1 expression between the sexes in adulthood, may be critical for the maturation and functioning of the neuroendocrine reproductive system and could possibly contribute to pubertal progression, sex differences in luteinizing hormone secretion, and other facets of reproductive physiology. It is therefore essential to understand how Kiss1 gene expression develops and what possible regulatory mechanisms govern the modulation of its expression. A number of recent studies, primarily in rodent or cell line models, have focused on the contributions of epigenetic mechanisms to the regulation of Kiss1 gene expression; thus far, mechanisms such as DNA methylation, histone acetylation, and histone methylation have been investigated. This review discusses the most recent findings on the epigenetic control of Kiss1 expression in adulthood, the evidence for epigenetic factors affecting Kiss1 expression during puberty and development, and findings regarding the contribution of epigenetics to the sexually dimorphic expression of Kiss1 in the hypothalamus.

Gender differences in neurodevelopment and epigenetics

The concept that the brain differs in make-up between males and females is not new. For example, it is well established that anatomists in the nineteenth century found sex differences in human brain weight. The importance of sex differences in the organization of the brain cannot be overstated as they may directly affect cognitive functions, such as verbal skills and visuospatial tasks in a sex-dependent fashion. Moreover, the incidence of neurological and psychiatric diseases is also highly dependent on sex. These clinical observations reiterate the importance that gender must be taken into account as a relevant possible contributing factor in order to understand the pathogenesis of neurological and psychiatric disorders. Gender-dependent differentiation of the brain has been detected at every level of organization--morphological, neurochemical, and functional--and has been shown to be primarily controlled by sex differences in gonadal steroid hormone levels during perinatal development. In this review, we discuss howthe gonadal steroid hormone testosterone and its metabolites affect downstream signaling cascades, including gonadal steroid receptor activation, and epigenetic events in order to differentiate the brain in a gender-dependent fashion.

Sex, stress, and epigenetics: regulation of behavior in animal models of mood disorders

Women have a higher incidence of stress related disorders including depression and generalized anxiety disorder, and epigenetic mechanisms likely contribute to this sex difference. Evidence from preclinical research suggests that epigenetic mechanisms are responsible for both sexual dimorphism of brain regions and sensitivity of the stress response. Epigenetic modifications such as DNA methylation and histone modifications can occur transgenerationally, developmentally, or in response to environmental stimuli such as stress exposure. This review will provide an overview of the various forms of epigenetic modifications observed in the central nervous system and will explain how these mechanisms contribute to a sexually dimorphic brain. It will also discuss the ways in which epigenetic alterations coincide with, and functionally contribute to, the behavioral response to stress across the lifespan. Ultimately, this review will focus on novel research utilizing animal models to investigate sex differences in epigenetic mechanisms that influence susceptibility to stress. Exploration of this relationship reveals epigenetic mechanisms with the potential to explain sexual dimorphism in the occurrence of stress related disorders.

The development of kisspeptin circuits in the Mammalian brain

The neuropeptide kisspeptin, encoded by the Kiss1 gene, is required for mammalian puberty and fertility. Examining the development of the kisspeptin system contributes to our understanding of pubertal progression and adult reproduction and sheds light on possible mechanisms underlying the development of reproductive disorders, such as precocious puberty or hypogonadotropic hypogonadism. Recent work, primarily in rodent models, has begun to study the development of kisspeptin neurons and their regulation by sex steroids and other factors at early life stages. In the brain, kisspeptin is predominantly expressed in two areas of the hypothalamus, the anteroventral periventricular nucleus and neighboring periventricular nucleus (pre-optic area in some species) and the arcuate nucleus. Kisspeptin neurons in these two hypothalamic regions are differentially regulated by testosterone and estradiol, both in development and in adulthood, and also display differences in their degree of sexual dimorphism. In this chapter, we discuss what is currently known and not known about the ontogeny, maturation, and sexual differentiation of kisspeptin neurons, as well as their regulation by sex steroids and other factors during development.

Organizational and activational effects of sex steroids on kisspeptin neuron development

Kisspeptin, encoded by the Kiss1 gene, is a neuropeptide required for puberty and adult reproductive function. Understanding the regulation and development of the kisspeptin system provides valuable knowledge about the physiology of puberty and adult fertility, and may provide insights into human pubertal or reproductive disorders. Recent studies, particularly in rodent models, have assessed how kisspeptin neurons develop and how hormonal and non-hormonal factors regulate this developmental process. Exposure to sex steroids (testosterone and estradiol) during critical periods of development can induce organizational (permanent) effects on kisspeptin neuron development, with respect to both sexually dimorphic and non-sexually dimorphic aspects of kisspeptin biology. In addition, sex steroids can also impart activational (temporary) effects on kisspeptin neurons and Kiss1 gene expression at various times during neonatal and peripubertal development, as they do in adulthood. Here, we discuss the current knowledge--and in some cases, lack thereof--of the influence of hormones and other factors on kisspeptin neuronal development.

Deciphering puberty: novel partners, novel mechanisms

Puberty is a fascinating developmental phase that involves the attainment of reproductive capacity and the completion of sexual and somatic maturation. As a life-changing event, puberty onset is precisely controlled by interconnected regulatory pathways that are sensitive to numerous endogenous signals and environmental cues. The mechanisms of normal puberty and its potential deviations have been thoroughly studied in humans and model species. Yet, characterization of the neurobiological basis of puberty is still incomplete. Progress on this front is not only relevant from a physiological perspective but would also help to unravel the underlying causes for the observed changes in the timing of puberty in humans, with a trend for earlier puberty onset, especially in girls. In this review, we will provide a synoptic overview of some recent developments in the field that have deepened our understanding of the neuroendocrine and molecular basis for the control of puberty onset. These include not only the demonstration of the involvement of the hypothalamic Kiss1 system in the control of puberty and its modulation by metabolic cues but also the identification of the roles of other neuropeptide pathways and molecular mediators in the regulation of puberty. In addition, the potential contribution of novel regulatory mechanisms, such as epigenetics, in the central control of puberty will be briefly discussed. Characterization of these novel players and regulatory mechanisms will improve our understanding of the basis of normal puberty and its eventual alterations in various pathological conditions.

Epigenetic mechanisms are involved in sexual differentiation of the brain

Sexual differentiation of the brain can be considered as a process during which effects of sex steroid hormones secreted during early development is maintained into adulthood. Epigenetic regulation is emerging as a potentially important mechanism of conveyance of long-lasting effects of the hormonal and environmental milieu in the developing brain. Evidence has accumulated to show that epigenetic regulation is involved in the control of sexual differentiation of the brain. In the preoptic area (POA), which is important for male sexual behavior, histones associated with the estrogen receptor (ER) α and aromatase (Arom) gene promoters are differentially acetylated between the sexes, and two subtypes of histone deacetylase (HDAC2 and 4) are associated with the same promoters at higher frequencies in males in the early postnatal period. Since ERα and Arom are essential genes in masculinization of the brain, these findings suggest that histone deacetylation in the early postnatal period is involved in masculinization of the brain. Indeed, inhibition of HDAC activity in males during this period abrogates brain masculinization: structural sexual dimorphism of the bed nucleus of the stria terminalis is eliminated and expression of male sexual behavior is reduced in adulthood. Previous reports have demonstrated that ERα gene expression in the POA is higher in females during the developmental and pubertal periods and in adulthood, indicating that sexually dimorphic ERα expression that appears in early postnatal development is maintained until adulthood by epigenetic programming. The ERα promoter is also more sparsely methylated in females, with an inverse correlation with ERα expression. In addition to the hormonal effect, the amount of maternal care received during postnatal development has a lasting effect on ERα expression mediated by DNA methylation of its promoter. Taken together, these results suggest that epigenetic mechanisms play a central role in the transduction and maintenance of early hormonal and social cues to organize sexually differentiated brain functions.

Polymorphisms in the maternal sex steroid pathway are associated with behavior problems in male offspring

OBJECTIVE

Slight perturbations in maternal sex steroid production and metabolism may interfere with normal fetal neurodevelopment. The balance of maternal estrogens and androgens may have direct fetal effects, may influence the fetal hypothalamic-pituitary-gonadal axis, or may alter local hormonal activity within the fetal brain. We investigated maternal functional polymorphisms of CYP17, CYP19, and CYP1B1, which control three major enzymatic steps in sex steroid biosynthesis and metabolism, in relation to childhood behaviors.

METHODS

The Mount Sinai Children's Environmental Health Study enrolled a multiethnic urban pregnancy cohort from 1998 to 2002 (n=404). DNA was obtained from maternal blood (n=149) and from neonatal cord blood (n=53). At each visit, mothers completed the Behavior Assessment System for Children, a parent-reported questionnaire used to evaluate children for behavior problems. We focused on problem behaviors more commonly associated with attention deficit-hyperactivity disorder (Hyperactivity, Attention Problems, Externalizing Behaviors, Conduct Disorder, Poor Adaptability) to determine whether maternal genetic variants in sex steroid production and metabolism influence sexually dimorphic behaviors in offspring.

RESULTS

The more active gene variants were significantly associated with Attention Problems and poorer Adaptive Skills in male compared with female offspring. The CYP19 variant allele was also significantly associated with worse scores for boys on the Hyperactivity, Externalizing Problems Composite, and Adaptive Skills Composite scales (P<0.05).

CONCLUSION

We observed maladaptive behaviors in the male offspring of mothers who carried functional polymorphisms in the sex steroid pathway. The strongest associations were in domains commonly affected in attention deficit-hyperactivity disorder.

Transient exposure of neonatal female mice to testosterone abrogates the sexual dimorphism of abdominal aortic aneurysms

RATIONALE

Abdominal aortic aneurysms (AAAs) exhibit marked sexual dimorphism with higher prevalence in men. Similarly, AAAs induced by angiotensin II (AngII) infusion into mice exhibit a higher prevalence in males. Testosterone promotes AAA pathology in adult male mice through regulation of angiotensin type 1A receptors (AT1aR) in abdominal aortas. However, mechanisms for sexual dimorphism of regional aortic angiotensin receptor expression and AAA formation are unknown.

OBJECTIVE

To define the role of developmental testosterone exposures in sexual dimorphism of AAAs, we determined if exposure of neonatal female mice to testosterone confers adult susceptibility to AngII-induced AAAs.

METHODS AND RESULTS

One-day-old female hypercholesterolemic mice were administered a single dose of either vehicle or testosterone. Neonatal testosterone administration increased abdominal aortic AT1aR mRNA abundance and promoted a striking increase in AngII-induced AAAs in adult females exhibiting low serum testosterone concentrations. AngII-induced atherosclerosis and ascending aortic aneurysms were also increased by testosterone administration to neonatal females. In contrast, neonatal testosterone administration in males had no effect on AngII-induced vascular pathologies. Deficiency of AT1aR in smooth muscle cells reduced effects of neonatal testosterone to promote AAAs in adult females but did not alter atherosclerosis or ascending aortic aneurysms. Testosterone increased AT1aR mRNA abundance and hydrogen peroxide generation in cultured abdominal aortic SMCs. Increased AT1aR mRNA abundance was maintained during progressive passaging of female smooth muscle cells.

CONCLUSIONS

These data reveal an unrecognized role of transient sex hormone exposures during neonatal development as long-lasting mediators of regional aortic AT1aR expression and sexual dimorphism of AAAs.

Sex differences in brain epigenetics

Sexual differentiation of the brain takes place during a perinatal-sensitive time window as a result of gonadal hormone-induced activational and organizational effects on neuronal substrates. Increasing evidence suggests that epigenetic mechanisms can contribute to the establishment and maintenance of some aspects of these processes, and that these epigenetic mechanisms may themselves be under the control of sex hormones. Epigenetic programming of neuroendocrine and behavioral phenotypes frequently occurs sex specifically, pointing to sex differences in brain epigenetics as a possible determinant. Understanding how sex-specific epigenomes and sex-biased responses to environmental cues contribute to the development of brain diseases might provide new insights for epigenetic therapy.

Epigenetic regulation of Kiss1 gene expression mediating estrogen-positive feedback action in the mouse brain

This study aims to determine the epigenetic mechanism regulating Kiss1 gene expression in the anteroventral periventricular nucleus (AVPV) to understand the mechanism underlying estrogen-positive feedback action on gonadotropin-releasing hormone/gonadotropin surge. We investigated estrogen regulation of the epigenetic status of the mouse AVPV Kiss1 gene locus in comparison with the arcuate nucleus (ARC), in which Kiss1 expression is down-regulated by estrogen. Histone of AVPV Kiss1 promoter region was highly acetylated, and estrogen receptor α was highly recruited at the region by estrogen. In contrast, the histone of ARC Kiss1 promoter region was deacetylated by estrogen. Inhibition of histone deacetylation up-regulated in vitro Kiss1 expression in a hypothalamic non-Kiss1-expressing cell line. Gene conformation analysis indicated that estrogen induced formation of a chromatin loop between Kiss1 promoter and the 3' intergenic region, suggesting that the intergenic region serves to enhance estrogen-dependent Kiss1 expression in the AVPV. This notion was proved, because transgenic reporter mice with a complete Kiss1 locus sequence showed kisspeptin neuron-specific GFP expression in both the AVPV and ARC, but the deletion of the 3' region resulted in greatly reduced GFP expression only in the AVPV. Taken together, these results demonstrate that estrogen induces recruitment of estrogen receptor α and histone acetylation in the Kiss1 promoter region of the AVPV and consequently enhances chromatin loop formation of Kiss1 promoter and Kiss1 gene enhancer, resulting in an increase in AVPV-specific Kiss1 gene expression. These results indicate that epigenetic regulation of the Kiss1 gene is involved in estrogen-positive feedback to generate the gonadotropin-releasing hormone/gonadotropin surge.