Epigenetics of Sex Differences in Brain and Behavior

描述（由申请人提供）：在精神健康和神经系统疾病的频率和强度方面存在强大的性别差异，这强调了需要确定介导大脑中性别差异组织的基本机制。发育暴露于性腺类固醇组织大脑和行为的持久变化是神经内分泌学的核心原则之一，但早期激素暴露赋予这些终身变化的机制仍然是未知的。在围产期的关键时期，雌激素可使实验大鼠的视前区（POA）发生性分化，从而为探索这些未知的机制提供了理想的模型系统。DNA甲基化是一种表观遗传过程，DNA甲基转移酶（DNMT）通过添加甲基基团共价修饰基因启动子区域内的胞嘧啶二核苷酸，导致染色质构象变化和基因沉默。我们的初步数据表明，新生儿男性和雌二醇治疗的女性有较低水平的DNMT活性和降低甲基化的基因与男性化的POA相比，女性。基于这些发现，我们假设雌二醇诱导的DNMT活性的性别差异组织持久的性别差异在神经形态和行为。我们的第一个目标（具体目标1）是确定DNMT活性的性别差异在维持性别特异性树突形态中的作用。与对照雌性相比，雄性和雄性化雌性中POA内树突棘突触的密度高2-3倍，并且这种模式从出生到成年一直保持。通过使用POA神经元/神经胶质细胞培养物的活细胞成像，我们将记录DNMT抑制后突触模式的动态变化。我们预测，低水平的DNMT活性（典型的新生儿男性）将导致在培养的POA神经元的雄性化树突棘密度和图案。我们的第二个目标（具体目标2）是将新生儿DNMT活性的性别差异与成年后的性别特异性行为联系起来。基于一个初步的发现，降低新生儿DNMT活性的性行为在成年后，我们预测，DNMT酶抑制在围产期的关键时期将导致雄性化的性行为在睾丸激素启动的成年雌性大鼠。最后，在具体目标3下，我们的目标是确定性别特异性DNMT活性的差异调节遗传靶点。我们将使用来自用DNMT抑制剂或载体处理的雄性和雌性动物的mRNA的全基因组微阵列分析来对差异基因表达进行分类。这些研究的完成将为大脑中维持性别差异的机制提供新的见解，并将首次解决生殖激素变化如何在整个生命周期中持续存在。这些研究对于理解心理健康和神经系统疾病病因学中的性别偏见以及理解大脑发育的基本机制具有重要意义。 公共卫生相关性：在精神健康和神经系统疾病的患病率和严重程度方面普遍存在强烈的性别偏见，这突出了理解大脑性别差异的生物学基础的重要性。研究新生儿发育过程中性别特异性基因表达模式的表观遗传控制，及其对性别特异性神经形态和行为组织的影响，是理解大脑发育的必要步骤，除了理解控制突触模式终身建立的机制。

DESCRIPTION (provided by applicant): The presence of robust gender differences in the frequency and intensity of mental health and neurological disorders underscores a need to identify the fundamental mechanisms mediating the organization of sex differences in the brain. That developmental exposure to gonadal steroids organizes enduring changes in brain and behavior is one of the central tenets of neuroendocrinology, but the mechanisms by which early hormone exposure imparts these life-long changes are still largely unknown. The preoptic area (POA) of the laboratory rat is sexually differentiated by estradiol during a perinatal critical period and thereby provides an ideal model system to explore these unknown mechanisms. DNA methylation is the epigenetic process by which a DNA methyltransferase (DNMT) enzyme covalently modifies cytosine dinucleotides within a gene's promoter region via addition of a methyl group, resulting in changes in chromatin conformation and gene silencing. Our preliminary data indicate that newborn males and estradiol-treated females have lower levels of DNMT activity and decreased methylation of genes associated with masculinization of the POA compared to females. Based on these findings, we hypothesize that estradiol-induced sex differences in DNMT activity organize enduring sex differences in neural morphology and behavior. Our first goal (Specific Aim 1) is to determine the role of sex differences in DNMT activity in maintaining sex-specific dendritic morphology. The density of dendritic spine synapses within the POA is 2-3 times higher in males and hormonally masculinized females compared to control females, and this pattern is maintained from birth through adulthood. With the use of live cell imaging of POA neuron/glia cultures, we will record dynamic changes in synaptic patterning following DNMT inhibition. We predict that low levels of DNMT activity (typical of the neonatal male) will result in masculinized dendritic spine density and patterning in cultured POA neurons. Our second goal (Specific Aim 2) is to associate sex differences in neonatal DNMT activity with sex-specific behavior in adulthood. Based on a preliminary finding that lowering neonatal DNMT activity defeminizes sexual behavior in adulthood, we predict that DNMT enzyme inhibition during the perinatal critical period will result in masculinized sex behavior in testosterone-primed adult female rats. Finally, under Specific Aim 3, our goal is to identify differentially regulated genetic targets of sex-specific DNMT activity. We will use a genome-wide microarray analysis of mRNA from male and female animals treated with DNMT inhibitors or vehicle to categorize differential gene expression. Completion of these studies will provide novel insight into the mechanisms maintaining sex differences in the brain and will address for the first time how hormonal changes established neonatally endure across the life-span. These studies have significance for understanding gender biases in the etiology of mental health and neurological disorders, as well as to understanding fundamental mechanisms of brain development. PUBLIC HEALTH RELEVANCE: The pervasiveness of strong gender biases in the prevalence and intensity of mental health and neurological disorders highlights the importance of understanding the biological basis of sex differences in the brain. Studying epigenetic control of sex-specific gene expression patterns during neonatal development, and its impact on the organization of sex-specific neural morphology and behavior, is a necessary step towards understanding brain development as a whole in addition to understanding the mechanisms controlling life-long establishment of synaptic patterning.