PRESENCE OF AN UNIDENTIFIED MYOSIN ISOFORM IN CERTAIN BOVINE FETAL MUSCLES

Genetic variation in the establishment of bovine muscle fibre types wa s studied by comparing muscle differentiation at 210 days of foetal li fe in normal cattle and in 'culard' animals, which have muscular hyper trophy. The different fibre types were determined by histochemical and immunohistochemical analyses with monoclonal antibodies specific to d ifferent myosin heavy chain isoforms. The isoforms were separated by e lectrophoresis and quantified by the ELISA method. Four muscles with d ifferent contractile and metabolic characteristics were studied : Semi tendinosus, Longissimus thoracis, Masseter (slow) and Cutaneus trunci (fast), Muscle fibres recognized by none of the antibodies used were o bserved in 'culard' foetuses in all the muscles studied and also in th e Cutaneus trunci of normal animals, Electrophoretic analysis showed n o particular myosin isoform in these muscles. It is possible therefore that the fibres contained a mysosin isoform until now unidentified in cattle, with a molecular weight the same as that of known isoforms, T his newly observed isoform seems to be specific to muscles rich in IIB fibres such as Cutaneus trunci and to the muscles of adult 'culard' c attle.