New Insights into Muscle Fiber Types in the Pig

• Published in: The journal of histochemistry and cytochemistry Vol. 50; no. 5; pp. 719 - 730
• Main Authors: Lefaucheur, Louis, Ecolan, Patrick, Plantard, Lydia, Gueguen, Naig
• Format: Journal Article
• Language: English
• Published: Los Angeles, CA Histochemical Soc 01.05.2002; SAGE Publications; Histochemical Society
• Subjects: Animals; Antibodies, Monoclonal; Base Sequence; Computer Science; Female; Histocytochemistry; In Situ Hybridization; Life Sciences; Molecular Sequence Data; Muscle Fibers, Skeletal - metabolism; Muscle, Skeletal - metabolism; Muscle, Skeletal - ultrastructure; Myosin Heavy Chains - metabolism; Protein Isoforms - metabolism; Ribonucleases; Swine; fiber types; immunocytochemistry; myosin heavy chains; mATPase histochemistry; pig skeletal muscle; in situ hybridization; HISTOLOGIE
• ISSN: 0022-1554; 1551-5044
• DOI: 10.1177/002215540205000513

The accurate classification of skeletal muscle fiber types according to myosin heavy chain (MyHC) polymorphism remains a difficult task in the pig. Combined myofibrillar ATPase and metabolic enzyme histochemistry, in situ hybridization, and immunocytochemistry were performed on serial transverse sections of pig longissimus (L) and rhomboideus (R) muscles at 100 kg body weight to give a new insight into muscle fiber typing in the pig. Several monoclonal antibodies (MAbs) either specific for a single MyHC (I, IIa, or IIb) or of multiple MyHCs (IIa + IIx or I + IIx + IIb) were used. No monospecific IIx antibody was available for the pig. All three adult Type II isoforms were expressed in the white L muscle, whereas no IIb was observed in the red R muscle, which was confirmed using RNase protection analysis. In most fibers, the distribution of the transcripts closely matched that of the corresponding proteins. When observed, co-expression of MyHCs mostly occured for IIx and IIb in L muscle, and was more common at the protein (11.5%) than at the mRNA (2.2%) level. A minor proportion of myofibers showed a mismatch between MyHC mRNA and protein. According to the type grouping distribution of myofibers encountered in pig muscle, MyHC isoform expression followed the rank order of I→Iia→Iix→IIb from the center to the periphery of the islets, concomitantly with a decrease in oxidative metabolism and an increase in fiber size. The developmental origin and functional significance of the type grouping distribution are discussed.