Onset of troponin synthesis in the chick wing bud.

Indirect antibody labeling techniques were used to determine when cells in the chick embryo wing bud begin to synthesize troponin. Frozen sections of stage 22 through stage 27 wing buds were treated with antibodies to the troponin complex and fluorescein-labeled antiimmunoglobulin. Cells producing detectable quantities of troponin were found first in late stage 24 or early stage 25 wing buds; all wing buds stage 25 and older contained labeled cells. Cells synthesizing troponin were initially localized in the muscle-forming areas of the wing bud nearest to the body wall. As the wing bud developed, cells located in more distal areas of the wing bud became labeled with fluorescent antibody, and the number of cells engaged in troponin synthesis increased in all areas. At all stages in which labeling occurred, some cells contained fluorescent cross-striations. When placed in the context of recent studies on the appearance of myofibrillar proteins, these results indicate that myogenic cells in the chick limb bud begin to synthesize large quantities of troponin at approximately the same time as the other muscle contractile proteins.