Single cell RNA sequencing of embryonic limb skeletal muscles

Fibroblasts are the most common cell type found in connective tissues, known to play major roles in development, homeostasis, regeneration and disease. Although specific fibroblast subpopulations were associated with different biological processes, the mechanisms and unique activities underlying their diversity has not been thoroughly examined. Turning to skeletal muscle development, we set to dissect the variation of muscle-resident fibroblasts (mrFibroblasts). Our results demonstrate mrFibroblasts diversify following the transition from embryonic to fetal myogenesis prior to birth. We find mrFibroblast segregate into two major subpopulations occupying distinct niches, with interstitial fibroblasts residing between the muscle fibers, and delineating fibroblasts sheathing the muscle mass. We further show these subpopulations entail distinct cellular dynamics and transcriptomes. Notably, we find mrFibroblast subpopulations exert distinct regulatory roles on myoblast proliferation and differentiation. Finally, we demonstrate this diversification depends on muscle contraction. Altogether, these findings establish mrFibroblast diversify in a spatio-temporal embryonic process into distinct cell types, entailing different characteristics and roles. We report the single cell RNA sequencing from skeletal muscles of E12.5&E15.5 embryos taken from both forelimbs and hindlimbs成纤维细胞（Fibroblasts）是结缔组织中最常见的细胞类型，已知其在发育、稳态、再生与疾病等生物学过程中发挥核心生物学功能。尽管已有研究表明特定成纤维细胞亚群与不同生物学过程相关联，但其多样性背后的生物学机制与独特生物学活性尚未得到全面解析。本研究聚焦于骨骼肌发育，旨在解析肌肉驻留成纤维细胞（muscle-resident fibroblasts, mrFibroblasts）的生物学多样性与分化多样化。研究结果显示，在出生前由胚胎肌发生（embryonic myogenesis）向胎儿肌发生（fetal myogenesis）的过渡阶段，肌肉驻留成纤维细胞即发生分化多样化。我们发现肌肉驻留成纤维细胞可分化为两种占据不同微环境的主要亚群：一类为肌纤维间的间质成纤维细胞（interstitial fibroblasts），另一类为包裹肌肉块的包膜成纤维细胞（delineating fibroblasts）。进一步研究表明，这两类亚群具备截然不同的细胞动力学特征与转录组谱（transcriptomes）。值得注意的是，我们发现肌肉驻留成纤维细胞亚群对成肌细胞（myoblast）的增殖与分化发挥着截然不同的调控作用。最终，我们证实该分化多样化过程依赖于肌肉收缩。综上，本研究结果证实，肌肉驻留成纤维细胞在胚胎发育的时空特异性进程中分化为不同的细胞类型，各自具备独特的生物学特性与功能。本研究报道了采自E12.5与E15.5胚胎前肢及后肢骨骼肌组织的单细胞RNA测序（single cell RNA sequencing）数据。