The expression of nestin delineates skeletal muscle differentiation in the developing rat esophagus

The muscularis externa of the developing rodent esophagus is initially composed of smooth muscle, and later replaced by skeletal muscle in a craniocaudal progression. There is growing evidence of distinct developmental origins for esophageal smooth and skeletal muscles. However, the identification of skeletal muscle progenitor cells is controversial, and the detailed cell lineage of their descendants remains elusive. In the current study, we carried out multiple labeling immunofluorescence microscopy of nestin and muscle type-specific markers to characterize the dynamic process of rat esophageal myogenesis. The results showed that nestin was transiently expressed in immature esophageal smooth muscle cells in early developing stages. After nestin was downregulated in smooth muscle cells, a distinct population of nestin-positive cells emerged as skeletal muscle precursors. They were mitotically active, and subsequently co-expressed MyoD, followed by the embryonic and later the fast type of skeletal muscle myosin heavy chain. Thus, the cell lineage of esophageal skeletal muscle differentiation was established by an immunotyping approach, which revealed that skeletal myocytes arise from a distinct lineage rather than through transdifferentiation of smooth muscle cells during rat esophageal myogenesis.