Assessment of the myostatin Q 204 X allele using an allelic discrimination assay

An allelic discrimination assay was designed and used to determine the genotypic and allelic frequencies of the myostatin (MSTN) gene Q204X allele from two Mexican Full-French herds. The assay is a simple high throughput genotyping method that could be applied to investigate the effect of the Q204X allele on the Charolais breed.

The myostatin (MSTN) gene is known to affect bovine carcass traits (Wilton 2003), the Q204X allele of this gene being present in French Charolais cattle (Grobet et al. 1997).Because of the impact of the MSTN gene on meat quality it is important to develop a highly sensitive, specific, cost-effective and easy to use DNA diagnostic test to determinate the presence of this allele.Current methods for Q204X genotyping in Charolais employ the restriction fragment length polymorphism polymerase chain reaction (RFLP-PCR) to identify the allele (Antoniou and Grosz 1999) and an oligonucleotide ligation assay for the simultaneous detection of bovine MSTN alleles is also available (Karim et al. 2000).
Compared with traditional PCR-based methods fluorescence-based single nucleotide polymorphism (SNP) detection assays offer several important advantages, including the absence of extensive post amplification manipulation (enzyme digestion, sequencing, etc.) and high throughput capacity (Livak et al. 1999).In this paper we describe the use of the allelic discrimination assay to genotype the MSTN gene Q204X allele in Mexican Charolais Full-French cattle derived from the European Charolais breed which segregates the MSTN Q204X allele.
Blood samples were obtained from 151 Mexican Full-French cattle from two herds kept at Nuevo Leon, Mexico.Herd 1, had been selected for improved lean beef and calving ease using founders from England, France and Ireland while herd 2 had been selected for conformation and weight gain traits using founders from France.Both herds provide dams, semen and natural service sires for use in nucleus and commercial herds and are considered as seed-stock for the Mexican Charolais Full-French in Mexico and in some Central America countries.Herds were evaluated according to their origin (Table 1).
The PCR amplification was performed using a reaction mixture containing 250 ng of sample DNA, 12.5 mL of Taqman PCR master mix (Applied Biosystems) and 0.625 mL of the assay mix (containing primers and probes for allelic discrimination) on an ABI Prism 7000 Sequence Detection System using 96-well optical reaction plates under the following conditions: one cycle of 2 min at 50 °C and 10 min at 95 °C followed by 40 cycles of 15 s at 92 °C and 1 min at 60 °C.Analysis of each genotype was performed by using the ABI Prism 7000 Sequence Detection System software, each sample being visually examined and false positives eliminated.
We found the Q204X allele in both herds but only the AB (A = Q204X allele, B = normal allele) heterozygous genotype was present in the cattle sampled (Table 1), which showed genotypic and allelic frequencies similar to those reported in Charolais populations from Eastern European countries (Dvorak et al. 2002).The Chi-squared test showed that there were significant differences in AB genotype frequencies between herds (p < 0.05), which may have been caused by selecting for the phenotypic and productive traits of interest within each herd.Dunner et al. (2003) has proposed that because MSTN gene presents a high allelic diversity it should be evaluated in all cattle populations.
We have found that the allelic discrimination approach is not only a simple, rapid and reproducible method for assessing the Q204X allele, but that the results for an individual genotype for this mutation can be quickly obtained in laboratories lacking access to real-time PCR equipment because allelic discrimination can be determined using traditional PCR and agarose gel electrophoresis.This method could be applied to asses the effect of the MSTN Q204X allele on double muscling as well as to establish mating systems focused on evaluating any association of this allele with growth and carcass traits.

Table 1 -
Allelic and genotypic frequencies of the myostatin Q204X allele.