Bifunctionality of Myocardin in Myogenesis

描述（由申请人提供）：细胞分化需要精确控制基因表达，主要是通过激活或抑制基因的转录因子。基因调控的扰动在发育和疾病中具有深远的影响，这在三种肌肉类型中尤为明显。虽然每种肌肉类型都有与靶基因表达相关的独特转录程序，但在发育和疾病期间，它们之间的基因表达存在一些重叠。因此，阐明肌肉受限基因表达的转录通路对于开发新的方法来重定向基因表达程序和优化干细胞向肌肉分化的条件至关重要。例如，平滑肌细胞（SMC）在其分化的遗传程序中是出了名的灵活，有文献证据表明它可以转分化和表型调节到更原始的状态。心肌素（心肌素）是SRF转录因子的一种有效的共激活因子，高度局限于SMC，可以执行SMC分化的近乎完整的程序，并在疾病状态下被调节。虽然心肌可激活许多SMC收缩基因，但其在诱导SMC生长抑制或收缩活性中的作用知之甚少。此外，我们尚未确定心肌在调节基因表达方面的全部潜力。本研究强有力的初步数据表明，心肌可引起SMC收缩能力和生长抑制，同时抑制骨骼肌分化程序。因此，我们假设心肌是肌肉分化的双功能调节剂。我们提出了三个具体目标，以检验这一论文使用创新的方法在遗传学。在Aim 1中，我们将通过改变细胞和转基因动物中的心肌表达来验证心肌是SMC收缩表型的充分和必要的激活剂的假设，以确定其对基因表达、生长和收缩能力的影响。在目标2中，我们将使用体外和体内模型来验证心肌是骨骼肌分化程序的有效抑制因子的假设，旨在阐明心肌这种新功能的机制。目的3将利用新的谱系追踪转基因小鼠来验证心肌蛋白在骨骼肌和SMC的共同祖细胞中表达的假设。总的来说，计划中的研究将对心肌作为SMC收缩表型的介质和骨骼肌命运的抑制因子的功能产生新的见解。这些信息对于调节肌肉疾病和干细胞分化的基因表达程序具有巨大的意义。细胞的特性是如何实现和维持的？是什么驱使细胞在疾病中改变其特性？一种方法是调节基因。在这里，我们提出针对一种能够促进一种肌肉细胞类型而不是另一种肌肉细胞类型的基因调节因子（心肌素）的研究。这些信息可直接应用于多种疾病，包括心脏和血管疾病、阿尔茨海默病和哮喘。

DESCRIPTION (provided by applicant): Cell differentiation requires exquisite precision in the control of gene expression, principally through transcription factors that either activate or repress genes. Perturbations in gene regulation have profound consequences in development and disease, and this is particularly evident with respect to the three muscle types. While each muscle type has a unique transcriptional program linked to target gene expression, there is some overlap in the expression of genes between them during development and disease. Thus, it is of critical importance to elucidate the transcriptional circuitry underlying muscle-restricted gene expression in order to develop novel approaches to redirect programs of gene expression that run askew and to potentially optimize conditions for the differentiation of stem cells into muscle. Smooth muscle cells (SMC), for example, are notoriously flexible in their genetic program of differentiation with documented evidence for both transdifferentiation and phenotypic modulation to more primitive states. Myocardin (Myocd), a potent coactivator of the SRF transcription factor, is highly restricted to SMC, can execute a near complete program of SMC differentiation, and is modulated in disease states. Though Myocd activates a number of SMC contractile genes, there is little knowledge as to its role in eliciting SMC growth suppression or contractile activity. Further, we have yet to define Myocd's full potential in regulating gene expression. Strong preliminary data in this proposal show that Myocd can elicit SMC contractile competence and growth suppression while repressing the skeletal muscle program of differentiation. Thus, we hypothesize that Myocd is a bifunctional regulator of muscle differentiation. We propose three specific aims to test this thesis using innovative methods in genetics. In Aim 1, we will test the hypothesis that Myocd is a sufficient and necessary activator of the SMC contractile phenotype by altering Myocd expression in cells and transgenic animals to determine effects on gene expression, growth, and contractile competence. In Aim 2, we will test the hypothesis that Myocd is a potent repressor for the skeletal muscle program of differentiation using in vitro and in vivo models aimed at illuminating mechanisms underlying this novel function of Myocd. Aim 3 will test the hypothesis that Myocd is expressed in common progenitors for skeletal muscle and SMC utilizing new lineage tracing transgenic mice. Collectively, the planned studies will yield novel insight into Myocd's function as both a mediator of the SMC contractile phenotype and as a repressor for skeletal muscle fate. Such information has enormous implications for modulating gene expression programs in the setting of muscle disease and stem cell differentiation. PUBLIC HEALTH RELEVANCE How is a cell's identity achieved and maintained and what drives a cell to change its characteristics in disease? One way is by regulating genes. Here, we propose studies aimed at one such regulator of genes (myocardin) that has the ability to promote one muscle cell type over another. This information has direct applications to a wide variety of diseases including those of the heart and blood vessels, Alzheimer's disease, and asthma.