Myosin heavy-chain mRNA is present in both myofibrillar and subsarcolemmal regions of muscle fibres

Abstract

Hybridization in situ with riboprobes to the myosin heavy-chain slow isoform showed that, in the rat soleus muscle, the myosin heavy-chain mRNA was distributed throughout the myofibres. There was greater density of autoradiographic grains in the subsarcolemmal regions of the fibres, but there was also a considerable number of grains in the core myofibrillar region of the fibres. Microdensitometry showed that the grain density in the myofibrillar region was approximately half that in the subsarcolemmal rim; this would correspond to some 70 % of the mRNA being present in the myofibrillar region. The results are consistent with the hypothesis that myosin is synthesized on polyribosomes present in the intermyofibrillar cytoplasm.

RNA Content Differs in Slow and Fast Muscle Fibers: Implications for Interpretation of Changes in Muscle Gene Expression

“…This conclusion is in line with the localization of the ribosomes (e.g., Horne and Hesketh 1990) and with ISH studies on whole-muscle cross-sections (e.g., Dix and Eisenberg 1988;Aigner and Pette 1990). The symmetric distribution of grains does not support an intermyofibrillar localization of RNA as suggested by a study of Hesketh et al (1991), who showed by ISH on longitudinal and transverse sections of soleus muscle of young rats that the MHC mRNA was distributed throughout the myofibers. They found greater density of grains in the subsarcolemmal regions of the fibers but there was also a considerable number of grains in the core myofibrillar region of the fibers.…”

Fiber-type-specific expression of essential (alkali) myosin light chains in human skeletal muscles.

“…1993Hughes et al, 1993;Jacobs-El et al. 1993;Billeter et al, 1992;Goldspink et al, 1992;Dix and Eisenberg, 1991;Hesketh et al, 1991;Kelly et al, 1991;Aigner andPette, 1990: Dix andEisenberg, 1988). As a general rule, differences in the content of a given protein among fiber types in adult skeletal muscles appear to result from differences in the availability of their mRNAs.…”

“…This type of distribution has been described for most of the mRNAs investigated in adult muscle thus far: myosin heavy chain mRNAs (Hesketh et al, 1991;Aigner and Pette, 1990;Dix et al, 1988); carbonic anhydrase 111 mRNA (Kelly et al, 1991); TNI (Koppe et al, 1989); and myogenic regulation factors (Hughes et al, 1993). The only study that found the mRNA distributed equally throughout the diameter of the fibers is our own report on the expression of ELC If and 3f in various chicken muscles (Billeter et al, 1992).…”

“…It was shown in animal models that the mRNAs coding for certain isoform families are expressed in a fiber type-specific manner (Billeter et al, 1992;Hesketh et al, 1991;Aigner and Pette, 1990;Diu and Eisenberg, 1988). For human muscle, few studies exist on the fiber type-specific expression of myofibrillar mRNAs, showing merely individual isoforms (Jostarndt et al, 1994;Soussi-Yanicostas and Butler-Browne, 1991;Brand et al, 1990).…”

Fast myosin light chain expression in chicken muscles studied by in situ hybridization.

“…Many of these isoforms are encoded on different genes, others are generated by differential splicing (Breitbart et al, 1987). In situ hybridizations with isoform specific probes for slow and fast myosin heavy chain mRNA (Hesketh et al, 1991;Brand et al, 1990;Aigner and Pette, 1990;Eisenberg, l988,1990,1991a,b,c), as well as troponin I mRNA (Koppe et al, 1989), have shown that these mRNAs are located in their respective fiber types and absent in the others. Our study extends these observations to the fast myosin light chain isoforms of chicken skeletal muscles.…”