Natural occurrence of fast- and fast/slow-muscle chimeric fibers in the expression of troponin T isoforms.

Rhomboideus, one of the back muscle tissues, and its single fibers were studied in chickens by immunostaining with antisera against fast- and slow-muscle-type troponin T isoforms. Nonuniform distribution of slow-muscle-type isoforms was for the first time detected in single fibers isolated from the muscle, although fast-muscle-type troponin T isoforms were distributed over the whole length of the fiber. Based on these observations, we conclude that fast- and fast/slow-muscle chimeric fibers exist in normal skeletal muscle tissue and that the existence of chimeric fibers is direct evidence showing that myonuclei subjected to different determination in troponin T isoform expression can together form a single muscle fiber.