Developmental regulation of cranial tendon fibroblast diversity and ECM interactions

项目总结/摘要 肌腱和韧带是功能性肌肉骨骼系统的基本组成部分。肌腱 将肌肉附着在骨骼上，并在称为附着点的不同附着点与这些组织相互作用 （骨）和肌腱连接（MTJ，肌肉）。这些相互作用导致基因的独特变化， 表达和细胞外基质（ECM）的产生，使肌腱承受由 肌肉收缩。转录因子如Scleraxis（Scx）指定早期肌腱祖细胞 （TPC）并调节ECM产生。我们之前发现了一种关键的ECM支架蛋白 在斑马鱼中称为血小板反应蛋白-4b（Tsp 4 b），由Scx调节， 维持和保存在人体肌腱中。不同类型的肌腱成纤维细胞（肌腱细胞） 对附着点或MTJ处ECM组装的影响仍不清楚。现时的建议 利用斑马鱼在体内进行单细胞RNA测序的优势解决了这些问题 成像和基因操作。拟议研究的长期目标是了解 肌腱/韧带中基因调控和ECM组装的空间动力学及其通过 机械力三个主要假设指导研究：1）不同亚型的TPC发展 2）腱细胞分泌的ECM调节力依赖性的肌间连接， 信号，改变这些不同的基因表达模式，在肌腱细胞和3）视黄酸是一种新的 力依赖信号控制肌腱发育。目标1将在肌腱细胞中进行scRNA-seq， 看看力是如何改变基因表达谱的目标2将研究Tsp 4 b、ECM和TGF-β的作用 肌腱中力依赖性基因表达的信号传导。目的3将研究RA信号通路在 钢筋束及其对机械载荷的响应。每个目标都结合了新颖的单细胞方法， 遗传操作、活体成像和定量方法，用于肌肉的生理刺激， 了解肌腱细胞特化和ECM组装对力的反应机制。

Project Summary/Abstract Tendons and ligaments are fundamental components of a functional musculoskeletal system. Tendons attach muscles to bone and interact with these tissues at distinct attachment sites called entheses (bone) and myotendinous junctions (MTJs, muscle). These interactions cause unique changes in gene expression and extracellular matrix (ECM) production that allow tendons to bear the forces exerted by muscle contraction. Transcription factors such as Scleraxis (Scx) specify early tendon progenitor cells (TPCs) and regulate ECM production. We previously discovered a critical ECM scaffolding protein called Thrombospondin-4b (Tsp4b) in zebrafish that is regulated by Scx, required for tendon maintenance and conserved in human tendons. How different types of tendon fibroblasts (tenocytes) are specified and influence ECM assembly at entheses or MTJs remains unclear. The current proposal addresses these issues using the advantages of the zebrafish for single cell RNA sequencing, in vivo imaging and genetic manipulation. The long-term goal of the proposed research is to understand the spatial dynamics of gene regulation and ECM assembly in tendons/ligaments and their regulation by mechanical force. Three primary hypotheses guide the research: 1) distinct subtypes of TPCs develop at entheses and MTJs in response to force, 2) ECM secreted by tenocytes regulates force-dependent signals that alter these distinct modes of gene expression in tenocytes and 3) retinoic acid is a novel force-dependent signal controlling tendon development. Aim 1 will perform scRNA-seq in tenocytes and see how force alters gene expression profiles. Aim 2 will study roles for Tsp4b, ECM, and TGF-beta signaling in force-dependent gene expression in tendons. Aim 3 will study the roles of RA signaling in tendons, and its responses to mechanical load. Each aim combines novel single cell approaches, genetic manipulation, live imaging and quantitative methods for physiological stimulation of muscles to get at mechanisms of tendon cell specification and ECM assembly in response to force.