Journal of Animal Science, Vol 70, Issue 6 1806-1813, Copyright © 1992 by American Society of Animal Science

JOURNAL ARTICLE

Tertiary myotubes in postnatal growing pig muscle detected by their myosin isoform composition

F. Mascarello, M. L. Stecchini, A. Rowlerson and E. Ballocchi
Istituto di Anatomia degli Animali Domestici con Istologia ed Embriologia, Facolta di Medicina Veterinaria, Milano, Italy.

The postnatal development of skeletal muscles was studied in growing pigs from 8 to 210 d of age. Indirect immunoperoxidase staining of frozen sections of porcine semimembranosus muscle and longissimus muscle revealed a distinct population of small fibers (tertiary myotubes) that were stained specifically by an antibody (anti-NE) selective for the developmental (embryonic and neonatal) isoforms of muscle myosin. At 8 d of age the other larger fibers were already anti-NE negative and differentiated into Types I and II. A gradual decrease in the number of anti-NE positive fibers together with a gradual increase in area of the remaining positive fibers was observed throughout the pigs' growth. These results may indicate that hyperplastic growth does not cease at birth. Possible mechanisms to explain the origin of these tertiary myotubes containing developmental isoforms of myosin are suggested.

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