Segmental Distribution of Myosin Heavy Chain Isoforms Within Single Muscle Fibers

Abstract

Despite many studies looking at the distribution of myosin heavy chain (MHC) isoforms across a transverse section of muscle, knowledge of MHC distribution along the longitudinal axis of a single skeletal muscle fiber has been relatively overlooked. Immunocytochemistry was performed on serial sections of rat extensor digitorum longus (EDL) muscle to identify MHC types I, IIA, IIX, IIY, and IIB. Sixteen fascicles which contained a total of 362 fibers were randomly and systematically sampled from the three EDL muscles. All MHC type I and type II isoforms were expressed. Segmental expression occurred within a very limited segment. MHC isoform expression followed the accepted traditional order from I⇔IIA⇔IIX⇔IIB, however, in some samples expression of an isoform was circumvented from IIB to I or from I to IIB directly. Segmental distribution of MHC isoforms along a single muscle fiber may be because of the myonuclear domain. Anat Rec, 300:1636-1642, 2017. © 2017 Wiley Periodicals, Inc.

Mixing it up: the biological significance of hybrid skeletal muscle fibers

“…4) (Zhang et al, 2010). Other more recent studies have reported similar patterns in normal mammalian muscles (Korfage et al, 2015;Zhang and Gould, 2017).…”

“…One of the most dramatic patterns of MHC and other myofibrillar isoform distribution is regional differences in protein content along the length of single fibers (Alway, 1993;Andersen, 2003;Bartnik et al, 1999;Brummer et al, 2013;Edman et al, 1988;Korfage et al, 2015;Larson et al, 2019;Lucas and Hoh, 2003;Lucas et al, 2018;Lutz et al, 2001;Maier, 1994;McLoon et al, 2011;Peuker and Pette, 1997;Rosser et al, 1995;Rubinstein and Hoh, 2000;Rubinstein et al, 2004;Sakuma et al, 1995;Snow et al, 2005;Staron and Pette, 1987;Zhang and Gould, 2017;Zhang et al, 2010). Such regional differences are consistent with the fact that frog muscle fibers exhibit major differences in shortening velocity in different segments from a single fiber (Edman et al, 1985).…”

“…Myonuclear domain size in mammalian muscle fibers ranges in volume from 20 to 100 µm 3 (Liu et al, 2009). Several authors have proposed that regional differences in MHC isoforms within hybrid fibers could be the result of differential expression among the myonuclei within these fibers (Brummer et al, 2013;McLoon et al, 2011;Stephenson, 2001;Zhang and Gould, 2017;Zhang et al, 2010). Indeed, the activity of multiple myonuclei within single fibers may differ significantly through time and space.…”

Transitional Hybrid Skeletal Muscle Fibers in Rat Soleus Development

“…A significant number of studies have now reported that unique MHC isoforms are frequently expressed within different segments of the same muscle fiber. 7,8,13,[41][42][43][44][45][46][47][48] A common interpretation of asymmetric MHC expression is that different myonuclear domains within single fibers may be uncoordinated in their myofibrillar gene expression. 7,8,42,46 Individual muscle fibers can be up to several millimeters long, and typically contain hundreds of myonuclei.…”

Spatial and temporal changes in myogenic protein expression by the microenvironment after freeze injury

“…The primary antibodies used are well characterized within our laboratory (Koishi et al 1995;Lee et al 2004Lee et al , 2018Zhang & Gould, 2017). In addition, there are mouse monoclonal antibodies against Pax7, myogenin F5D or neonatal F59 (Developmental Studies Hybridoma Bank), MyoD 5.8A (BD Biosciences) or embryonic fast MY32 (Sigma); rabbit polyclonal antibodies against Myf5, MyoD M-318 and myogenin M-225 (Santa Cruz); goat polyclonal antibody against Pax3 (Abcam); p38MAPK and phosphorylated p38MAPK (Cell Signalling).…”