Regulated Retrotransposon Elements in Neuroendocrine System

描述(由申请人提供)： 生物学和发育中的一个中心问题是描绘表观遗传和核结构事件的序列，通过这些事件，转录单位从沉默切换到活跃，从异染色质区域重新定位到常染色质区域。 脑下垂体是所有脊椎动物神经内分泌系统的重要组成部分，在维持动态平衡、新陈代谢、生殖、生长和哺乳过程中起着至关重要的作用。在来自下丘脑的中枢神经系统信号和来自外周器官的反馈信号的综合控制下，脑下垂体合成和分泌不同类型内分泌细胞的营养激素。尽管现在已经很好地定义了脑下垂体细胞谱系的关键调控因子，但分子事件的时空顺序的机制仍有待揭示，在这些分子事件中，前体细胞中沉默的基因最终在成熟的腺体中被激活，导致对基因表达的精确的、细胞限制的调控。 在这一点上，生长激素基因，虽然最初是沉默的，然后在生长激素和促乳素的共同前体中被激活，但在促乳素中变得积极抑制。然而，控制GH表达的确切分子机制仍然不清楚。初步数据表明，在小鼠生长激素基因座的远端调节区中存在一个绝缘体元件，它可能起到建立不同染色质修饰的独立区域的作用。有趣的是，已鉴定的假定绝缘子元件属于正弦反转录转座子家族，已被证明在形成真核基因组中具有深远的作用，并被认为是人类疾病的病原体。我打算研究：1)这个假定的绝缘体元件是否在垂体发育中起作用，如果是，确定其作用的分子机制；2)组蛋白甲基转移酶SET结构域家族的一个特定成员ESET是否提供了GH基因调控启动子核间移位的关键分子机制。这两个特定的目标将在体内实现：将产生转基因小鼠并进行分析，以评估该反转录转座子和ESET蛋白在控制GH基因表达中的作用。 更深入地了解在发育中的垂体腺模型系统中调节重新定位和最终基因表达的过程，不仅可能导致基因激活的一般原理，而且还可能开发出与生长相关的疾病的新疗法。

DESCRIPTION (provided by applicant): A central question in biology and development is to delineate the sequence of epigenetic and nucleo-architectural events by which transcription units "switch" from silenced to active, relocating from heterochromatic to euchromatic regions. The pituitary gland is a critical component of the neuroendocrine system present in all vertebrates, and is essential in the maintenance of homeostasis, metabolism, reproduction, growth, and lactation. Under the integrated control of central nervous system signals from the hypothalamus and feedback signals from peripheral organs, the pituitary gland synthesizes and secretes trophic hormones from distinct endocrine cell types. Although key regulators involved in the specification of pituitary cell lineages are now well defined, the mechanisms underlying the spatial and temporal order of molecular events by which genes silenced in precursor cells are ultimately activated in the mature gland, leading to precise, cell-restricted regulation of gene expression are still to be unveiled In this regard, the GH gene, while initially silenced, is then activated in a common precursor for somatotropes and lactotropes, but becomes actively repressed in lactotropes. Yet, the precise molecular mechanisms controlling GH expression remain vague. Preliminary data indicates that an insulator element exists within a distal regulatory region of the mouse growth hormone gene locus that may act to establish independent domains of differential chromatin modifications. Interestingly, the identified putative insulator element belongs to the family of SINE retrotransposons, which have been shown to have a profound role in shaping eukaryotic genomes and are recognized as a causal agent for human disease. I propose to investigate: 1) whether this putative insulator element functions in pituitary development and, if so, to determine the molecular mechanism of its action, and 2) whether a specific member of the SET domain family of histone methyl transferases, ESET, provides the key molecular mechanism underlying the shift of nuclear compartments of the GH gene regulatory promoter. These two specific aims will be addressed in vivo: transgenic mice will be generated and analyzed to evaluate the role of this retrotransposon and the ESET protein in the control of the GH gene expression. Deeper understanding of the processes regulating the timing of relocation and ultimate gene expression in the model system of the developing pituitary gland, may not only lead to general principles in gene activation, but also to the development of new therapies for growth-related diseases.