The enlarged muscles of certain breeds of cattle, such as the Belgian Blue, result from a marked increase in the number of normal sized muscle fibres. Originally insulin-like growth factors (IGFs) were implicated in this myofibre hyperplasia. Recently it has been reported that mice lacking a myostatin gene, a member of the TGFb super family, have enhanced skeletal muscle mass resulting from increased muscle fibre number and size. Mutations in this gene have been found in double muscled cattle, indicating that myostatin is an inhibitor of muscle growth. Myostatin is expressed early in gestation and then maintained to adulthood in certain muscles. Myostatin expression in bovine muscle is highest during gestation when muscle fibres are forming and some of the myogenic regulatory factors have elevated expression over the same period as myostatin. Myostatin and MyoD, myogenic regulatory factors expressed in muscle have been shown to differ between normal and hypertrophied muscle cattle breeds. This evidence strongly suggests that lack of functional myostatin is associated with an increase in fibre number which then results in a marked increase in potential muscle mass in double muscled cattle.

J, Bass, J Oldham, M Sharma, and R Kambadur

Proceedings of the New Zealand Society of Animal Production, Volume 59, , 291-293, 1999
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