Myogenic Cell Lineages and Muscle Fiber Type Formation

描述（由申请方提供）：脊椎动物骨骼肌纤维来源于在发育过程中多次出现的成肌细胞前体细胞。这些肌纤维显示出收缩和代谢基因表达的多样性，这些基因建立并维持收缩速度和代谢能力的表型多样性。肌纤维对诸如神经支配的外部信号的响应的可塑性在很大程度上决定了它们的快肌纤维与慢肌纤维类型的身份。这种流行的观点主要基于大量的胎儿（次级）肌纤维研究。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。这些纤维最初在功能性神经支配的情况下形成，但在肌球蛋白重链（MyHC）基因的表达和肌纤维类型方面显示出多样性。这种多样性是基于不同的成肌细胞谱系形成这些快和快/慢初级肌纤维的承诺。从这些不同的成肌细胞谱系调节快和快/慢初级肌纤维发育的机制是完全未知的，因为没有合适的脊椎动物模型系统可用于其研究。本研究提出了这样一个模型系统，并报告了初步研究，建立了控制成肌细胞谱系致力于不同肌纤维类型形成的机制的基本原理和可行性。特定目标要解决的中心假设是：不同初级肌纤维类型的发育受转录因子LHX 9和一小群激活慢MyHC 2启动子的转录辅助调节因子介导的细胞自主性、谱系特异性机制调节。本研究的具体目的是：1.在快/慢与快肌源性细胞谱系中激活慢MyHC 2基因启动子的转录复合物的鉴定和表征，2.确定LIM同源结构域转录因子LHX 9在细胞谱系依赖性肌纤维类型特化中的作用，以及3.鉴定LHX 9蛋白-蛋白相互作用调节缓慢MyHC 2基因表达。这些研究将提供重要的洞察肌肉表型的分子和细胞调控过程中的发展和再生疾病状态。

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.