Regulation of expression of avian slow myosin heavy-chain isoforms.
The slow tonic anterior latissimus dorsi (ALD) muscle of the chicken contains two isomyosins, namely SM-1 and SM-2. The proportions of the two isoforms change with age, SM-2 expression increasing at the expense of SM-1. Applying a load on the wing increases the rate and extent of SM-1 replacement. Here we have demonstrated that decreasing the load by removal of the distal portion of the wing in 1-week-old chickens had an effect opposite to that of overloading in that it slowed muscle growth and the rate of SM-1 elimination. Experimental unloading of muscles previously weighted for 1 or 3 weeks slowed the growth rate of muscles, with consequent regression of relative hypertrophy; however, it did not lead to the reexpression of SM-1 myosin. This indicates that the overload-induced changes in myosin expression are not readily reversible. Nerve section produced unexpected results, in that it advanced the normal developmental shift in myosin expression toward predominance of the SM-2 isoform, similar to the effect of muscle overload.
Department of Medicine, University of Chicago, IL 60637.
S K
SK
Reid
J M
JM
Kennedy
N
N
Shimizu
A
A
Stewart
G
G
Vrbova
R
R
Zak
D000818:Animals; D002645:Chickens; D005786:Gene Expression Regulation; D007536:Isomerism; D009121:Muscle Denervation; D009218:Myosins / Q000235:genetics*
D009218:Myosins