Maternal Programming of Gene Expression Through DNA Methylation

描述(由申请人提供)：幼崽的母爱影响大鼠下丘脑-垂体-肾上腺(HPA)对压力的反应。因此，自然地表现出更频繁地舔/梳理幼崽和弓背哺乳的母亲(即高LG-ABN母亲)的成年后代对压力的反应更温和。这些效应在一定程度上是通过海马糖皮质激素受体(GR)基因表达的变化来调节的。我们提出了一个描述这种母性效应的细胞和分子基础的工作模型。母亲护理的变化增加了5-羟色胺(5-HT)在海马区的周转，进而通过5-HT7受体激活cAMP的形成，增加了蛋白激酶A的活性，并增加了激活蛋白-2(AP-2)和NGFI-A的表达，后者通过与相关GR基因启动子序列的直接相互作用反式激活GR基因的转录。关键的问题涉及这些影响的明显持久性：产妇保健如何在后代的生命周期内规划基因表达的差异？我们的研究旨在检验这样一种假设，即这种影响是由位于GR基因启动子区域特定位置的DNA序列的结构变化所介导的。这些研究使用体内和体外方法来研究产妇护理如何改变DNA甲基化，以及这种DNA、染色质结构、基因表达和生理的化学变化之间的关系。这些方法包括用亚硫酸氢钠作图分析单核苷酸甲基化，用染色质免疫沉淀分析组蛋白修饰和DNA-蛋白质相互作用。我们相信，这些研究有可能为产妇护理对大脑中的基因表达从而对表型发育产生长期影响的机制提供明确的描述。从本质上讲，这些研究直接考察了与特定功能性状相关的X基因环境交互作用。最后，尽管通常不愿使用这样的描述，但据我们所知，这些研究可能提供了第一个对DNA结构变化的描述，以响应有丝分裂后的环境事件，并最终可能提供环境诱导的DNA甲基化和染色质结构在整个寿命内可塑性的初步研究。

DESCRIPTION (provided by applicant): Maternal care of pups influences the development of hypothalamic-pituitary-adrenal (HPA) responses to stress in the rat. Thus, the adult offspring of mothers that naturally show an increased frequency of pup licking/grooming and arched back nursing (ie, High LG-ABN mothers) show more modest HPA responses to stress. These effects are, in part, mediated by changes in hippocampal glucocorticoid receptor (GR) gene expression. We propose a working model describing the cellular and molecular basis for this maternal effect. The changes in maternal care increase serotonin (5-HT) turnover in the hippocampus which, in turn, activates cAMP formation via a 5-HT7 receptor and to increase protein kinase A activity and increased expression of activator protein-2 (AP-2) and NGFI-A which transactivate GR gene transcription via direct interaction with relevant GR gene promoter sequences. The critical questions concern the apparent permanence of these effects: How might maternal care program differences in gene expression over the lifespan of the offspring? Our studies are designed to examine the hypothesis that such effects are mediated by structural changes in DNA sequences located at specific sites within the promoter region of the GR gene. These studies use both in vivo and in vitro approaches to examine how maternal care alters DNA methylation and the relationship between such chemical alterations of the DNA, chromatin structure, gene expression and physiology. The methods include analysis of single nucleotide methylation using sodium bisulfite mapping, histone modifications and DNA-protein interactions with chromatin immunoprecipitation assays. We believe that these studies hold the possibility of providing a clear description of the mechanisms by which maternal care exerts long-term effects over gene expression in the brain and thus of phenotypic development. In essence, these studies directly examine gene X environment interactions in relation to specific, functional trait. Finally, although normally loath to use such descriptions, to the best of our knowledge these studies potentially provide the first description of structural changes in DNA in response to a post-mitotic, environmental event, and may ultimately provide the initial studies of environmentally-induced plasticity in DNA methyation and chromatin structure over the lifespan.