The gradual expression of troponin T isoforms in chicken wing muscles.

Troponin T (TnT) is one of the muscle regulatory proteins and is thought to be related to unique contractile properties in diverse muscles and also to myogenesis. The expression of TnT isoforms in the chicken wing muscles was investigated by two-dimensional gel electrophoresis and immunoblotting with an antiserum against fast skeletal muscle TnT. The upper arm muscles, M. biceps brachii and M. triceps brachii, showed striking differential expression of high molecular weight B type and low molecular weight L type TnT isoforms in the proximal, middle and distal portions of each muscle. The ratio of the total quantity of B type TnT isoforms to that of L type TnT isoforms decreased gradually along the proximo-distal axis of the wing. The upper arm muscles, M. deltoideus and M. tensor patagii longus, and most of the lower arm muscles examined in this study did not show such differential expression. The lower arm muscles, M. flexor carpi ulnaris and M. extensor carpi radialis longus, showed some gradual expression of TnT isoforms, but the B/L ratio in the former slightly increased along the proximo-distal axis. The gradual expression in M. biceps brachii was not found in the 1-day-old chick, but was established by 30 days post-hatching. The biological significance of differential expression of TnT isoforms in different muscles and even in single muscles was speculated upon with respect to muscle contractile regulation and myogenesis.