Myogenic Cell Lineages and Muscle Fiber Type Formation

描述(申请人提供)：脊椎动物骨骼肌纤维起源于成肌细胞前体细胞，在发育过程中多次出现。这些肌肉纤维在收缩和代谢基因的表达上表现出多样性，这些基因建立和保持了收缩速度和代谢能力的表型多样性。肌肉纤维对外部信号如神经的反应的可塑性在很大程度上决定了它们的快肌纤维类型与慢肌纤维类型的一致性。这一流行的概念主要是基于对胎儿(次级)肌肉纤维的大量研究。然而，很少有研究集中在初级肌发生过程中调节肌纤维类型形成的机制。这些纤维最初在缺乏功能神经的情况下形成，但在肌球蛋白重链(MyHC)基因和肌肉纤维类型的表达上表现出多样性。这种多样性是基于不同的成肌细胞谱系对这些快和快/慢的初级肌肉纤维的形成的承诺。由于还没有合适的脊椎动物模型系统来研究这些不同的成肌细胞系中的快和快/慢的初级肌肉纤维的发育，其机制是完全未知的。这项研究提案提出了这样一个模型系统，并报告了初步研究，为研究控制成肌细胞谱系承诺形成不同肌肉纤维类型的机制奠定了基础和可行性。具体目标要解决的中心假设是：不同初级肌肉纤维类型的发育受转录因子LHX9和激活慢速MyHC2启动子的一小部分转录辅助调节因子介导的细胞自主、谱系特异性机制的调节。这项研究的具体目的是：1.鉴定和鉴定在快/慢和快肌细胞系中激活慢速MyHC2基因启动子的转录复合体；2.确定LIM同源结构域转录因子LHX9在细胞谱系依赖的肌肉纤维类型规范中的作用；以及3.鉴定调节慢速MyHC2基因表达的LHX9蛋白-蛋白质相互作用。这些研究将为了解肌肉表型在疾病状态下的发育和再生过程中的分子和细胞调控提供重要的见解。 公共卫生相关性：脊椎动物骨骼肌纤维起源于成肌细胞前体细胞，这些细胞在发育过程中多次出现。这些肌肉纤维在收缩和代谢基因的表达上表现出多样性，这些基因建立和保持了收缩速度和代谢能力的表型多样性。这些研究将为了解肌肉表型在疾病状态下的发育和再生过程中的分子和细胞调控提供重要的见解。

DESCRIPTION (provided by applicant): Vertebrate skeletal muscle fibers originate from myoblast precursor cells that appear at multiple times during development. These muscle fibers display diversity in expression of contractile and metabolic genes that establish and maintain phenotypic diversity in contraction speed and metabolic capacity. The plasticity of muscle fibers with regard to their response to extrinsic signals such as innervations largely determines their fast versus slow muscle fiber type identity. This prevailing notion is based mostly on the large number of studies of fetal (secondary) muscle fibers. However, very few studies have focused on the mechanisms that regulate muscle fiber type formation during primary myogenesis. These fibers form initially in the absence of functional innervations and yet display diversity in expression of myosin heavy chain (MyHC) genes and muscle fiber type. This diversity is grounded in the commitment of distinct myoblast cell lineages to the formation of these fast and fast/slow primary muscle fibers. The mechanisms that regulate the development of fast and fast/slow primary muscle fibers from these distinct myoblast cell lineages are completely unknown since no appropriate vertebrate model system has been available for their investigation. This research proposal presents such a model system and reports preliminary studies that establish the rationale and feasibility for investigation of the mechanism that controls myoblast cell lineage commitment to distinct muscle fiber type formation. The central hypothesis to be addressed by the specific aims is: Development of different primary muscle fiber types is regulated by cell autonomous, lineage-specific mechanisms mediated by the transcription factors LHX9 and a small cohort of transcriptional co-regulators that activate the slow MyHC2 promoter. The specific aims for the research are: 1. Identification and characterization of the transcriptional complex that activates the slow MyHC2 gene promoter in the fast/slow versus fast myogenic cell lineage, 2. Determine the role of the LIM homeodomain transcription factor, LHX9, in cell lineage-dependent muscle fiber type specification, and 3. Identification of LHX9 protein-protein interactions that regulate slow MyHC2 gene expression. These studies will provide important insight into the molecular and cellular regulation of muscle phenotype during development and regeneration from disease states. PUBLIC HEALTH RELEVANCE: Vertebrate skeletal muscle fibers originate from myoblast precursor cells that appear at multiple times during development. These muscle fibers display diversity in expression of contractile and metabolic genes that establish and maintain phenotypic diversity in contraction speed and metabolic capacity. These studies will provide important insight into the molecular and cellular regulation of muscle phenotype during development and regeneration from disease states.