Expression of eight distinct MHC isoforms in bovine striated muscles: evidence for MHC-2B presence only in extraocular muscles.
This study aimed to analyse the expression of myosin heavy chain (MHC) isoforms in bovine muscles, with particular attention to the MHC-2B gene. Diaphragm, longissimus dorsi, masseter, several laryngeal muscles and two extraocular muscles (rectus lateralis and retractor bulbi) were sampled in adult male Bos taurus (age 18-24 months, mass 400-500 kg) and analysed by RT-PCR, gel electrophoresis and immunohistochemistry. Transcripts and proteins corresponding to eight MHC isoforms were identified: MHC-alpha and MHC-beta/slow (or MHC-1), two developmental isoforms (MHC-embryonic and MHC-neonatal), three adult fast isoforms (MHC-2A, MHC-2X and MHC-2B) and the extraocular isoform MHC-Eo. All eight MHC isoforms were found to be co-expressed in extrinsic eye muscles, retractor bulbi and rectus lateralis, four (beta/slow, 2A, 2X, neonatal) in laryngeal muscles, three (beta/slow, 2A and 2X) in trunk and limb muscles and two (beta/slow and alpha) in masseter. The expression of MHC-2B and MHC-Eo was restricted to extraocular muscles. Developmental MHC isoforms (neonatal and embryonic) were only found in specialized muscles in the larynx and in the eye. MHC-alpha was only found in extraocular and masseter muscle. Single fibres dissected from masseter, diaphragm and longissimus were classified into five groups (expressing, respectively, beta/slow, alpha, slow and 2A, 2A and 2X) on the basis of MHC isoform electrophoretical separation, and their contractile properties [maximum shortening velocity (v(0)) and isometric tension (P(0))] were determined. v(0) increased progressively from slow to fast 2A and fast 2X, whereas hybrid 1-2A fibres and fibres containing MHC-alpha were intermediate between slow and fast 2A.
Toniolo
L
L
Dipartimento di Anatomia e Fisiologia Umana, Università di Padova, Italy.
Maccatrozzo
L
L
Patruno
M
M
Caliaro
F
F
Mascarello
F
F
Reggiani
C
C
D000704:Analysis of Variance; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D020869:Gene Expression Profiling; D007150:Immunohistochemistry; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D017931:DNA Primers; D020033:Protein Isoforms; D018995:Myosin Heavy Chains