Single cell RNA sequencing of the limb myotendionous junction

Vertebrate muscles and tendons are derived from distinct embryonic origins yet they must interact in order to facilitate muscle contraction and body movements. How robust muscle tendon junctions (MTJs) form to be able to withstand contraction forces is still not understood. Using techniques at a single cell resolution we reexamined the classical view of distinct identities for the tissues composing the musculoskeletal system. We identified fibroblasts that have switched on a myogenic program and demonstrate these dual identity cells fuse into the developing muscle fibers along the MTJs facilitating the introduction of fibroblast-specific transcripts into the elongating myofibers. We suggest this mechanism resulting in a hybrid muscle fiber, primarily along the fiber tips, enables a smooth transition from muscle fiber characteristics towards tendon features essential for forming robust MTJs. We propose that dual characteristics of junctional cells could be a common mechanism for generating stable interactions between tissues throughout the musculoskeletal system. We report the single cell RNA sequencing from the region of a P0 myotendinous junction taken from forelimbs脊椎动物的肌肉与肌腱虽源自不同的胚胎起源，却必须相互协作以支持肌肉收缩与躯体运动。然而，能够承受收缩力的强健肌肉-肌腱连接点（muscle tendon junctions, MTJs）究竟如何形成，目前仍未明确。本研究借助单细胞分辨率技术，重新审视了组成肌肉骨骼系统的各类组织具有独特身份的经典观点。我们鉴定出了激活肌源性程序的成纤维细胞，并证实这类具有双重身份的细胞会沿肌肉-肌腱连接点融合进入发育中的肌纤维，从而将成纤维细胞特异性转录本引入正在延伸的肌纤维中。我们认为，这种主要沿肌纤维末端形成杂合肌纤维的机制，能够实现从肌纤维特性向肌腱特性的平滑过渡，这对形成强健的肌肉-肌腱连接点至关重要。我们提出，连接细胞的双重特性可能是在整个肌肉骨骼系统中实现组织间稳定相互作用的通用机制。本研究报道了从前肢采集的P0阶段肌肉-肌腱连接点区域的单细胞RNA测序数据。