Fig. 4. Chicken muscle fibers formed in transplanted quail somatopleure show the chicken pattern of fiber-type. Donor quail somatopleure replaced that of the host chicken embryo adjacent to somites 16-23 in ED2 embryos, and the pectoral muscles were isolated and sectioned at ED10. (A) The absence of quail-specific antigen staining (red) in muscle fibers (blue) demonstrates the chicken origin of these fibers in the chimeric pectoral muscle. (B) Chicken fibers within the chimeric pectoral muscle rarely express slow MyHCs. (C,D) At the same position within the contralateral control side of the chicken pectoral muscle, there is no quail contribution to either muscle or stromal cells, and as expected, no slow fibers are found within this region. Scale bar is 100 µm.