A novel single nucleotide polymorphism ( SNP ) of the IGF 1 R gene and the association with growth traits in yak ( Brief Report )

The insulin-like growth factor-I (IGF1) is a peptide growth factor that exerts mitogenic and metabolic activities, which are regulators of growth, survival and cell differentiation in a number of cell and tissue types. To elicit its effects, IGF1 must bind its receptors. The insulinlike growth factor 1 receptor (IGF1R) is similar to insulin receptor (INSR) and it mediates the growth-promoting effect of IGF1. The IGF1R gene, therefore, was selected as a biological candidate gene for growth, body composition, metabolic, and skeletal traits in animals (ROTHSCHILD et al. 1997). By now, no polymorphism of yak (Bos grunniens) IGF1R gene is reported. In the present paper, the partial exon 1 region of IGF1R was screened to detect the SNPs in Chinese yak breeds. Associations of SNP of IGF1R with growth traits were analysed.


Background
The insulin-like growth factor-I (IGF1) is a peptide growth factor that exerts mitogenic and metabolic activities, which are regulators of growth, survival and cell differentiation in a number of cell and tissue types.To elicit its effects, IGF1 must bind its receptors.The insulinlike growth factor 1 receptor (IGF1R) is similar to insulin receptor (INSR) and it mediates the growth-promoting effect of IGF1.The IGF1R gene, therefore, was selected as a biological candidate gene for growth, body composition, metabolic, and skeletal traits in animals (ROTHSCHILD et al. 1997).By now, no polymorphism of yak (Bos grunniens) IGF1R gene is reported.In the present paper, the partial exon 1 region of IGF1R was screened to detect the SNPs in Chinese yak breeds.Associations of SNP of IGF1R with growth traits were analysed.

Primer sequences
As any of yak IGF1R gene sequences was not available, the primer pairs were designed based on bovine partial IGF1R gene (acc.no.NM174305).5'-ACC CGC CAA GAA ATT GTT TC-3' 5'-GGC TCC TCC ATA CTT CCT GTA-3' PCR conditions 50 ng of genomic DNA in a 20 μl reaction containing 1.5 mM MgCl2, 0.2 mM of each dNTP, 0.5 U of Taq DNA polymerase (TaKaRa, China) and 0.4 μM of each primer.The cycling protocol conditions included an initial denaturation cycle at 94 °C for 5min, followed by 30 cycles of denaturation at 94 °C for 1 min, annealing at 57.5 °C for 30 s, 72 °C for 45 s.Then, the amplified products were subjected to a final extension at 72 °C for 10 min.Polymorphism of IGF1R was detected by SSCP in 12 % PAGE in constant voltage (200V) for 12-15 h after its PCR products was denatured 10 min at 98 °C.The gel was stained with silver nitrate and visualized with 2 % NaOH solution (supplied with 0.1 % formaldehyde) (PAN et al. 2007).The PCR fragments from different SSCP patterns were subcloned and sequenced.

Result
A novel SNP was discovered in the exon 1 region of the IGF1R gene among 404 unrelated one-year-old animals which belonged to five yak breeds in China (Datong yak, 72; Tianzhu White yak, 111; Gannan yak, 133; Qinghai Plateau yak, 70; Xingjiang yak, 50).Gene and genotype frequencies of the discovered SNP were shown in Table 1.According to acc.no.BTU33122, the SNP was at nt437 within exon 1 of the coding sequence, but caused no amino acids exchange.The SNP found in the yak IGF1R gene enable to conduct association analyses in order to evaluate the SNP as a genetic marker for breeding.As IGF1R binds IGFs which has effects on growth and reproduction, the association of genotypes (the C>A of exon I) with growth traits were analysed in yak (Table 2).The associations were analysed by the least-squares method as applied in the general linear model (GLM) procedure of SPSS according to the following statistical model: with y ijk is the studied traits, μ is the overall mean; B i is the fixed effect of breed, S j is the fixed effect of sex, M k is the IGF1R genotype effect, e ijk is the random residual effect.The result indicated the different genotype of IGF1R exon 1 had a significant effect on traits including of body weight, body height, body slanting length (P<0.05),but the genotype did not affected on cannon circumference and heart girth.This result provoked the IGF1R gene as important candidate gene for production trait.

Table 1
Allele and genotype frequencies of PCR-SSCP at exon 1 region of IGF1R gene in five populations Relative Häufigkeit von Allelen und Genotypen einer PCR-SSCP im Exon 1 des IGF1R Gens in fünf Yak-Populationen

Table 2
Effects of different genotypes of the exon 1 SNP of IGF1R Gene on production traits Effekte verschiedener Genotypen des Exon 1 SNP im IGF1R Gen auf Produktionsmerkmale