Fig. 3. Chicken muscle fibers formed within quail pectoral stroma show the chicken pattern of fiber-type. Chicken somites were transplanted into quail embryos at ED2 and the pectoral muscles were isolated and sectioned at ED10. (A) As evidenced by the lack of staining for the quail-specific antigen (red) within muscle fibers (blue), the half of the pectoral muscles receiving a contribution from transplanted somites contain muscle fibers derived from the chicken. (B) Chicken fibers within the chimeric pectoral muscle rarely express slow MyHCs. (C) Muscle fibers on the contralateral control side of this pectoral muscle are exclusively derived from quail somites as evidenced by the ubiquitous quail-specific marker, and (D) many of the quail muscle fibers within this location are of the slow phenotype (green). Scale bar is 100 µm.