Role of homeobox proteins in muscle development

描述（由申请人提供）：典型肌肉调节因子和相关调节蛋白对骨骼肌发育的调节已被深入研究。然而，同源盒蛋白在肌肉发育中的作用仍不太清楚。我们之前在体外证明了同源盒转录因子Barx2促进成肌细胞分化并调节肌肉特异性基因的表达。我们的初步体内研究表明，Barx2在胚胎成肌细胞和卫星细胞中表达，表明Barx2缺失小鼠在肌肉发育方面存在缺陷。我们提出的研究重点是确定Barx2在胚胎肌肉发育（Aim 1）和成人肌肉功能和修复（Aim 2）中的作用，并确定可能介导这些活动的分子靶点（Aim 3）。为了确定Barx2对胚胎肌肉发育的影响，我们将确定其是否与成肌细胞的迁移、增殖和分化标志物共表达，测试Barx2阴性成肌细胞的增殖和分化潜能，并检查胚胎和围产期Barx2阴性小鼠四肢的肌肉块。通过分析Barx2缺失小鼠的快、慢纤维类型的比例和测量Barx2在成年肌肉中的收缩力来检测Barx2在成年肌肉中的功能。将使用急性（心毒素诱导的损伤）和慢性（mdx营养不良小鼠）肌肉损伤模型来检验Barx2在卫星细胞介导的肌肉修复中的作用。为了确定可能控制肌肉发育的Barx2靶点，我们将对Barx2零型和野生型肌肉的mRNA进行微阵列分析，并使用我们开发的新的染色质免疫沉淀（ChlP）克隆方法来发现Barx2的基因组结合位点。明确Barx2在肌肉发育、功能和修复中的作用，有助于更全面地了解肌肉调节网络，从而有助于诊断或治疗肌肉疾病。

DESCRIPTION (provided by applicant): The regulation of skeletal muscle development by the canonical muscle regulatory factors and associated regulatory proteins has been intensively investigated. The role of homeobox proteins in muscle development, however, remains less well understood. We showed previously that the homeobox transcription factor Barx2 promotes myoblast differentiation and regulates muscle specific gene expression in vitro. Our preliminary in vivo studies show that Barx2 is expressed in embryonic myoblasts and satellite cells and suggest that the Barx2 null mouse has defects in muscle development. Our proposed studies focus on defining the roles of Barx2 in embryonic muscle development (Aim 1) and in adult muscle function and repair (Aim 2), and on identifying the molecular targets that may mediate these activities (Aim 3). To define the influence of Barx2 on embryonic muscle development, we will determine whether it is co- expressed with markers of migrating, proliferating and differentiating myoblasts, test the proliferation and differentiation potential of Barx2 null myoblasts, and examine muscle masses in embryonic and perinatal Barx2 null mouse limbs. The function of Barx2 in adult muscle will be examined by analyzing the ratio of fast to slow fiber types and measuring contractile muscle force in Barx2 null mice. Models of both acute (cardiotoxin-induced injury) and chronic (mdx dystrophic mice) muscle injury will be used to examine the role of Barx2 in satellite cell-mediated muscle repair. To identify the targets of Barx2 that may control muscle development, we will perform microarray analysis of mRNA from Barx2 null and wild type muscle and use a new chromatin immunoprecipitation (ChlP)-cloning methodology that we have developed to discover genomic binding sites for Barx2. Defining the roles of Barx2 in muscle development, function and repair should help to build a more complete understanding of the muscle regulatory network that may aid in diagnosing or treating muscle disease.