Stable silencing of spinal motor neuron enhancers by transiently expressed Nkx2.2

 描述（由申请人提供）：多细胞生物发育的标志是多能细胞协调分化为不同的有丝分裂后细胞类型。这个过程 依赖于以协调方式激活末端效应基因表达并抑制在其它谱系中表达的基因的转录程序。虽然已经取得了进展，在确定转录激活因子和机制，通过它们建立新的细胞身份，目前知之甚少的替代发展计划的渐进式抑制的过程。具体而言，许多控制神经细胞分化的转录抑制因子在神经上皮的早期模式化期间仅瞬时表达，并且尚未确定这些抑制因子是否仅作用于神经祖细胞中表达的基因，或者它们是否可以以持续的方式沉默增强子以前瞻性地修改基因表达，即使在它们下调之后。在这里，我们将研究瞬时表达的运动神经元阻遏物Nkx2.2对它结合的增强子的染色质修饰和对小鼠运动神经元祖细胞中基因表达模式的影响（而Nkx2.2是异位表达的）及其下调。Nkx2.2在稳定沉默的增强子中的功能将通过缺失Nkx2.2结合基序进行实验测试。这些研究将揭示多细胞生物体中细胞终末分化过程中稳定沉默或活性增强子的基本机制。由于沉默的增强子需要在细胞命运重编程过程中恢复到活性或平衡状态，因此我们的研究结果可能有助于开发更有效的患者细胞重编程策略，用于诊断和治疗目的。

 DESCRIPTION (provided by applicant): The hallmark of multicellular organism development is concerted differentiation of pluripotent cells into diverse postmitotic cell types. This process relies on transcriptional programs that in a coordinated manner activate expression of terminal effector genes and repress genes expressed in other lineages. While progress has been made in identifying transcriptional activators and mechanisms through which they establish new cell identities, little is currently known about the process underlying progressive repression of alternative developmental programs. Specifically, many transcriptional repressors that control differentiation of neural cells are expressed only transiently during early patterning of neuroepithelium and it has not been determined whether these repressors act solely on genes expressed in neural progenitors or whether they can silence enhancers in a persistent fashion to prospectively modify gene expression even following their downregualtion. Here we will examine effects of a transiently expressed motor neuron repressor Nkx2.2 on chromatin modifications of enhancers it binds and on patterns of gene expression in mouse motor neuron progenitors (while Nkx2.2 is ectopically expressed) and following its downregulation. Function of Nkx2.2 in enhancers that are stably silenced will be experimentally tested by deletion of Nkx2.2 binding motif. Together these studies will reveal fundamental mechanisms underlying stable silencing of poised or active enhancers during terminal differentiation of cells in multicellular organisms. As silenced enhancers need to be reverted into an active or poised state during cell fate reprogramming, our findings might be instrumental for the development of more efficient patient cell reprogramming strategies for diagnostic and therapeutic purposes.