Myostatin in dogs - Study of the MSTN gene to determine mutations causing loss of its regulatory function: PCR amplification and sequencing, with determination of homozygosity or heterozygosity.

Myostatin is a protein encoded by the MSTN gene that acts as a negative factor to reduce the development of skeletal muscle mass, controlling the total number of muscle fibers through regulation of the total number of myoblasts. When there is a deletion in this gene, the protein is expressed in smaller amounts and, as consequence more muscle fibers (myofibrils) are produced than necessary.

This gene encodes the synthesis of a ligand (preprotein), known as myostatin or growth-differentiation factor-8 [GDF8], of the TGF-b protein superfamily (transforming growth factor-beta -TGF-b-). Ligands of this family bind to several TGF-b receptors that lead to the recruitment and activation of transcription factors of the SMAD family that regulate gene expression. Myostatin is synthesized as a precursor protein that, when proteolytically processed in a dibasic site, generates an N-terminal propeptide called myostatin-propeptide (MPRO) and a C-terminal dimer linked by disulfide bridges, which is the biologically active part. This protein negatively regulates the proliferation and differentiation of skeletal muscle cells. Mutations in this gene are associated with an increase in skeletal muscle mass in mammals and humans.

Mosher et al. (in Mosher DS, Quignon P, Bustamante CD, Sutter NB, Mellersh CS, et al. A mutation in the myostatin gene increases muscle mass and enhances Racing performance in heterozygote dogs. PLoS Genet, 2007, 3 (5): e79. doi: 10.1371 / journal.pgen. 0030079), discovered a mutation in the canine myostatin MSTN gene, a negative muscle mass regulatory gene that affects muscle composition and as consequence, the speed in the greyhounds. Dogs that have only one copy of the gene with the mutation (M*/ M) are more muscular than normal and are faster in racing competitions. However, dogs with both copies with the mutation (M*/M*) are very muscular, which is not a competitive advantage. In dogs, the genetic alteration of the MSTN gene consists of a deletion of two base pairs in the third exon of the MSTN gene that generates a stop codon at amino acid 313.

In heterozygous runner dogs (greyhounds) (M*/M), the mutation has been associated with greater athletic potential with its corresponding advantages in competitive races, while if they are homozygous for the mutation (M*/M*) they are too muscular, with intimidating appearance and slower in the races. These dogs exhibit a striking physique that includes wider heads, short legs and thick waist. These characteristics and not their temperament led to the name "Bully whippets" (intimidating greyhounds). These same mutations have been described in other dog breeds, such as the "American Bully", among others.

Mutations of this gene have been described in several species of mammals such as cattle, horses, sheep, mice, etc., and even in humans (Myostatin-related muscle hypertrophy).

These mutations are inherited with an incomplete autosomal dominant inheritance pattern, that is, they are partially expressed when one of the copies of the gene exists with the mutation and completely when there are two copies of the gene with the mutation.

To know the probability of obtaining descendants with the affectation, the following calculation can be followed according to the paired animals:

• If two affected homozygotes mate (M*/M*), 100% of the offspring will be affected homozygous (M*/M*). 

• If an affected homozygote (M*/M*) with a carrier heterozygote (M*/M) is paired, 50% will be affected homozygotes (M*/M*) and the other 50% will be heterozygous carriers (M*/M). 

• If an affected homozygote (M*/M*) is paired with a normal homozygous (M/M), 100% will be heterozygous carriers (M*/M). 

• If a carrier heterozygote (M*/M) with a normal homozygote (M/M) is paired, 50% will be normal homozygous (M/M) and 50% carrier heterozygous (M*/M). 

• If two normal homozygotes (M/M) mate, 100% will be normal homozygous (M/M). 

Tests performed in IVAMI

• Molecular detection of mutations in the myostatin MSTN gene, by genomic amplification (PCR), followed by gene sequencing. 

• Determination of homozygosity or heterozygous mutations. 

Recommended samples:

• Uncoagulated blood in tube extracted with EDTA for separation of blood leukocytes, or uncoagulated blood extracted with EDTA and deposited several drops on absorbent paper sheet to let dry and send by postal mail (IVAMI can mail the card to deposit the blood sample). 

Sample preservation

• Uncoagulated blood sample in tube: refrigerated for a maximum of 48 hours. Shipping by courier in a white cork box with frozen pack. 

• Sample of dried blood on absorbent paper sheet: room temperature. Shipping by postal mail. 

Delivery of results:

• 4 to 5 working days. 

Cost of the tests:

• Molecular detection of mutations in the myostatin gene including the study of the homozygosity or heterozygosity of the mutations detected, by genomic amplification (PCR), followed by sequencing of the gene: Consult to ivami@ivami.com.