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 (Pa tapoutian et al. [1995] Science 270: 1818-1821), We characterize skeletal m uscle precursors in mouse esophagus by investigating the expression of four myogenic regulatory factor transcripts: MyoD, Myf-5, myogenin, and MRF4. M yf-5 was first detected at cranial region of esophageal muscle at 12-13 day s of gestation, followed by coexpression of MyoD and MRF4 at 14 days of ges tation, and myogenin at embryonic day 15. The expression of these myo-genic factors showed outer to inner layer and cranial to caudal progression duri ng fetal and early postnatal development of mouse esophagus. The early appe arance of myogenic regulatory factors starting at 12-13 days of gestation i ndicates that the cells in the mouse esophageal wall are committed to becom e skeletal muscle-type cells before any differentiated smooth or skeletal m uscle cells are observed at 14-15 days of gestation (C) 2000 Wiley-Liss, In c.