SHORT COMMUNICATION

 

Polymorphisms of the CAST gene in the Meishan and five other pig populations in China

 

 

Q.S. Wang^I; Y.C. Pan^I,; L.B. Sun^II; H. Meng^I

^IDepartment of Animal Science, School of Agriculture and Biology, Shanghai Jiaotong University, Shanghai 201101, P.R. China
^IIShanghai Institute of Veterinary Hygienic, Shanghai 200232, P.R. China

 

 

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ABSTRACT

The aim of the study was to characterize the polymorphism of the Calpastatin (CAST) gene identified with three restriction enzymes (TaqI, HinfI, MspI) in Meishan and five other pig populations, and to provide information on their potential in marker-assisted selection and conservation. Meishan pigs appeared to be monomorphic at loci CAST/HinfIand CAST/MspI. A high frequency of the favoured genotype, FF, in terms of meat quality was detected in Meishan pigs, a breed well known for high quality meat. However, the frequency of the genotype, FF, was very low in Sutai pigs, a breed developed from a Duroc (50%) * Meishan (50%) cross. This is probably partially due to the fact that genetic improvement in this breed was achieved through the use of traditional quantitative genetics. It is suggested that traditional selection techniques combined with the use of the polymorphisms discovered have an important potential to improve overall meat quality.

Keywords: Polymorphism, CAST, Meishan, Sutai

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Calpastatin (CAST), which is an endogenous inhibitor (Ca2+ dependent cysteine proteinase), plays a central role in the regulation of calpain activity in cells (Murachi et al., 1981; Murachi, 1983; Forsberg et al., 1989) and is considered to be one of the major modulators of the calpains. There is evidence that the activity of CAST from the skeletal muscle is highly related to the rate of meat tenderization and protein turnover after slaughter (Koohmaraie et al., 1991; Goll et al., 1998; Sensky et al., 1998; Parr et al., 1999; Hao et al., 2000). Therefore, the CAST gene represents an excellent candidate gene for studying variation in pork quality (Ernst et al., 1998).

Ernst et al. (1998) amplified the porcine CAST gene fragment encompassing intron 6 and identified RFLP polymorphism with restriction endonuclease, HinfIand MspI. Before these markers could be used efficiently in breeding and management decisions, studies with different populations would be necessary. The Meishan breed is famous for its prolificacy and good meat quality. However, only a small population is presently being conserved and the status of favoured genes is not known. Sutai is a breed developed by the Breeding Centre of Taihu Pig, China from the cross between the Duroc (50%) and the Meishan (50%). It is important to know whether the traditional selection method can concentrate favoured genes as successfully as marker-assisted selection (MAS). Li et al. (2006) have reported the present genetic status by analyzing the polymorphism of H-FABP, MC4R and ADD1 genes in Meishan and four other pig populations (Sutai, Landrace × Sutai, Yorkshire × Sutai, Duroc × Landrace × Yorkshire). The aim of this study was to detect new polymorphisms of the CAST gene and compare all the tested loci in the six populations to provide further information for MAS and their conservation.

The studies included 235 unrelated fatteners of the following breeds/populations: 28 Meishan (M), 27 Sutai (S), 15 Yorkshire × Sutai (YS), 15 Landrace × Sutai (LS), 25 Duroc × Landrace × Yorkshire (DLY) and 125 PIC hybrid pigs (L402×Cambrough).

Genomic DNA was isolated according to Kanai et al. (1994). One pair of primer was designed in the porcine CAST cDNA sequence (M20160) to find new SNPs by sequencing. The primer sequences were: forward primer, 5'-GTGATGACAAAAAACTTGACG-3'; and reverse primer, 5'-TCATCCTTATCCAAGA GATGTC-3'. The CAST genotype was identified with the restriction enzymes HinfIand MspI, according to the method used by Ernst et al. (1998). Data were analyzed using the FREQ procedures of SAS 6.12 (SAS, 1998).

In this study, we amplified the porcine CAST gene fragment encompassing part of exon 24, intron 24 and part of exon 25. After sequencing the 1991 bp DNA fragment, a C/T transition was determined in intron 24. A novel RFLP polymorphism with restriction endonuclease TaqI was developed on this position. After digestion with the endonuclease, three genotypes were identified. The AA genotype has three fragments, 963 bp, 806 bp and 222 bp; the AB genotype has four fragments, 1028 bp, 963 bp, 806 bp and 222 bp; and the BB genotype has two fragments, 1028 bp and 963 bp. Experiments are in progress to evaluate their influence on meat traits in pigs.

The frequencies of genotypes at loci CAST/TaqI, CAST/HinfIand CAST/MspIin the tested populations (235 pigs) are shown in Table 1. The present study shows that Meishan pigs appeared to be monomorphic at loci CAST/HinfI and CAST/MspI. Only the DD genotype at the locus CAST/HinfIand the FF genotype at the locus CAST/MspIwere found in Meishan. A similar distribution of CAST genotypes in the Meishan breed was reported by Ernst et al. (1998). Both the earlier studies by Li et al. (2006) and current results indicated that the Meishan breed is a conserved population with a special genetic background, and should be conserved as a valuable genetic resource.

 

 

Animals with genotype FF at locus CAST/MspI appeared to be less fatty (thinnest backfat and lower weight of backfat with skin in login) compared with the other two genotypes. Moreover, genotype FF at locus of CAST/MspI was the most advantageous for eye-muscle area when compared to the remaining genotypes (Kuryl et al., 2003, Krzecio et al., 2005). The high frequency of the favoured genotype, FF, in Meishan pigs could be responsible for their good meat quality. The Sutai breed was developed from the cross between the Duroc (50%) and Meishan (50%) breeds. Presently, Sutai is used mainly as a maternal line to cross with Landrace or Yorkshire boars to produce commercial pigs that compete mainly with Duroc × Landrace × Yorkshire in the pork market. However, data from the current study showed that the Sutai has the lowest frequency of the beneficial FF genotype among the six pig populations. This is probably partially due to selection for trait improvement using traditional quantitative genetics, which resulted in selection into one direction. The pig industry should launch a new breeding project to increase the frequency of beneficial genotypes. Moreover, the current study stated that the beneficial FF genotype was present in all the breeds and populations tested, which may provide significant improvements for the pig industry as it can be used in MAS to produce naturally tender and juicy pork.

The present finding demonstrated that all possible genotypes at the loci of the CAST gene considered here were found in the Sutai and the PIC hybrid pigs. Thus, the two breeds could be chosen as experimental material for evaluation of the effect of CAST genotype on meat and carcass quality traits. In addition, further research will be performed on the relationship of the polymorphism of CAST gene with meat and carcass quality traits in the six populations.

Highly significant differences in allele frequencies of the loci CAST/TaqIand CAST/MspIwere observed between the Meishan and the other five populations (Table 2). The loci CAST/HinfI and CAST/MspI are in linkage disequilibrium in the M, S, LS, YS breeds with a Meishan background while the extra haplotype occurs in the European DLY and PIC breeds. It appears that some breed differences exist for allele frequencies at all tested loci. The compared result of the HinfI alleles among the six populations was almost the same as the MspI alleles which are not shown in the Table 2.

 

 

Highly significant differences in alleles frequencies at all the loci considered, existed between the six populations. The traditional selection method in the development of the Meishan and Sutai is based on quantitative genetics and not on molecular genetics. The results obtained indicate that selection based on quantitative genetics cannot concentrate effectively on favoured genes. Therefore, this combined with the use of the polymorphisms discovered would increase the accuracy of selection and improve rates of genetic progress for meat traits.

 

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 30671492), the National Basic Research Program of China (No. 2004CB117502) and the Shanghai Municipal Key Project of Agriculture, Science and Technology (No.2003.01-1).

 

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# Corresponding author. E-mail: panyc@sjtu.edu.cn