ARS | Publication request: Extreme muscle development in sheep heterozygous for both myostatin and callipyge mutations

Submitted to: Plant and Animal Genome Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: November 7, 2008
Publication Date: January 10, 2009
Repository URL: http://www.intl-pag.org/17/abstracts/W11_PAGXVII_084.html
Citation: Smith, T.P., Freking, B.A., Shackelford, S.D., King, D.A., Wheeler, T.L., Leymaster, K.A. 2009. Extreme muscle development in sheep heterozygous for both myostatin and callipyge mutations. Plant and Animal Genome Conference Proceedings. Jan. 10-14, 2009. San Diego, CA. Abstract W084.

Technical Abstract: Two mutations causing increased muscle size and decreased fat content in sheep have been described. The callipyge (CLPG) syndrome is only exhibited after 4 to 6 weeks of age in animals inheriting the mutation solely from their sire. In contrast, a mutation of the myostatin gene (MSTN) in the Texel breed exhibits a primarily additive mode of inheritance with a phenotype observable in animals of about the same age as with callipyge. The two mutations ultimately act through distinct signaling pathways, so our hypothesis was that phenotypic effects in animals expressing both mutations would be additive or synergistic. The hypothesis was tested by producing a group of 12 rams of similar genetic background yet heterozygous for both mutations, and then breeding them to a group of 220 non-carrier crossbred ewes. This created animals of four pertinent genotypes (mmcc, Mmcc, mmCc, and MmCc, where upper case denotes the mutant alleles of MSTN and CLPG, respectively), but lacking animals expressing callipyge and homozygous for the myostatin mutation. The Mmcc genotype had no visible effect in this crossbred genetic background and the mmCc genotype had an effect approximately equal to previously reported effects for the callipyge syndrome. However, the combination of the two mutations had a dramatic and synergistic effect with the animals displaying leg scores beyond those observed with just callipyge. Data are currently under analysis to quantify the full range of effects including attributes of meat quality.