Skeletal muscle precursors in mouse esophagus are determined during early fetal development

Mouse esophageal muscle is composed of skeletal muscle in the adult, but it has been proposed to be derived from differentiated smooth muscle cells by transdifferentiation during late fetal and early postnatal development (Patapoutian et al. [1995] Science 270:1818-1821). We characterize skeletal muscle precursors in mouse esophagus by investigating the expression of four myogenic regulatory factor transcripts: MyoD, Myf-5, myogenin, and MRF4. Myf-5 was first detected at cranial region of esophageal muscle at 12-13 days of gestation, followed by coexpression of MyoD and MRF4 at 14 days of gestation, and myogenin at embryonic day 15. The expression of these myogenic factors showed outer to inner layer and cranial to caudal progression during fetal and early postnatal development of mouse esophagus. The early appearance of myogenic regulatory factors starting at 12-13 days of gestation indicates that the cells in the mouse esophageal wall are committed to become skeletal muscle-type cells before any differentiated smooth or skeletal muscle cells are observed at 14-15 days of gestation.