Relationship between myosin heavy chain isoform expression and muscling in several diverse pig breeds

¹ Research Institute for the Biology of Farm Animals (FBN), Wilhelm-Stahl-Allee 2, 18196 Dummerstorf
² Institute of Animal Science, Animal Breeding and Husbandry Group, University of Bonn, Endenicher Allee 15, 53115 Bonn

^* To whom correspondence should be addressed. E-mail: s.wimmers{at}fbn-dummerstorf.de.

	Abstract

The objective of this study was to examine the relationship of the relative abundance of transcripts of myosin heavy chain (MyHC) isoforms and muscling in several diverse pig breeds. The animals used were from 3 pure breeds (Pietrain, Duroc, and Mongcai), and 2 crosses (Duroc x Pietrain (DUPI) and Duroc x Berlin Miniature Pigs (DUMI)). Real-time PCR quantification of MyHC isoforms I, IIa, IIx, and IIb showed that the relative expression of MyHC IIb was higher in pigs with large longissimus muscle areas in both DUPI (69.6% vs. 53.0%) and DUMI (60.5% vs. 47.5%). In DUPI, similar transcript levels of MyHC I were found in both large and small longissimus muscle (14.7% and 15.2%), whereas in DUMI animals these values were 18.4% and 33.5% (P<0.05). The groups of animals with large and small longissimus muscle area in the DUPI also tended to differ in MyHC IIa and IIx transcripts. The comparison among different breeds confirmed the trend of high MyHC IIb transcript abundance going together with high muscularity. In Pietrain, Duroc, DUPI, and DUMI, abundance of MyHC IIb accounted for more than half of the MyHC transcripts (65.4%, 59.7%, 54.0%, and 54.0%). Mongcai showed very low MyHC IIb (11.4%), but high type I, IIa, and IIx relative RNA levels (24.1%, 28.5%, and 35.9%). Frequencies of fibers, determined by ATPase muscle fiber staining, and relative abundance of MyHC isoforms, determined by quantitative RT-PCR, of corresponding pairs of type I, IIa, and IIx/IIb were significantly correlated (r = 0.71, 0.67, and 0.52, respectively). The study demonstrates that IIb fibers are the most prominent in pigs having large longissimus muscle area and implies that IIb is the determining fiber contributing to the differentiation of large and small loineye muscle area in the pig.

Key Words: longissimus dorsi, myosin heavy chain, pig, real time PCR, 0

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