Epigenetics of Sex Differences in Brain and Behavior

描述（由申请人提供）：在心理健康和神经疾病的频率和强度方面存在着明显的性别差异，这强调了需要确定调解大脑中性别差异组织的基本机制。神经内分泌学的核心原则之一是，在发育过程中暴露于性腺类固醇会导致大脑和行为发生持久的变化，但早期暴露于激素导致这些终身变化的机制在很大程度上仍是未知的。实验大鼠的视前区（POA）在围产期关键时期由雌二醇进行性别分化，从而为探索这些未知机制提供了理想的模型系统。DNA甲基化是DNA甲基转移酶（DNMT）通过添加甲基共价修饰基因启动子区域内的胞嘧啶二核苷酸的表观遗传过程，导致染色质构象的改变和基因沉默。我们的初步数据表明，与雌性相比，新生雄性和雌二醇处理的雌性具有较低水平的DNMT活性，并且与POA雄性化相关的基因甲基化降低。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了神经形态和行为的持久性别差异。我们的第一个目标（Specific Aim 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。雄性和激素雄性化的雌性在POA内的树突棘突触密度比对照雌性高2-3倍，并且这种模式从出生到成年一直保持。利用POA神经元/胶质细胞培养的活细胞成像，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（典型的新生儿雄性）将导致培养的POA神经元的树突棘密度和模式男性化。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期性别特异性行为联系起来。基于一项初步发现，降低新生儿DNMT活性会使成年期的性行为去女性化，我们预测围产期关键时期的DNMT酶抑制会导致睾酮启动的成年雌性大鼠的性行为雄性化。最后，在Specific Aim 3下，我们的目标是确定性别特异性DNMT活性的差异调控遗传靶点。我们将使用全基因组微阵列分析来自雄性和雌性动物的mRNA，这些动物接受DNMT抑制剂或载体治疗，以分类差异基因表达。这些研究的完成将为维持大脑性别差异的机制提供新的见解，并将首次解决新生儿激素变化如何在整个生命周期中持续的问题。这些研究对于理解心理健康和神经疾病病因中的性别偏见，以及理解大脑发育的基本机制具有重要意义。

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.