Two novel SNPs of the ABCG2 gene and its associations with milk traits in Chinese Holsteins

Abstract

The ATP-binding cassette transporter ABCG2 (also known as breast cancer resistance protein, BCRP) belongs to the ATP-binding cassette (ABC) family of transmembrane drug transporters, playing a crucial role in the protection of various cells and tissues against xenotoxins and/or endotoxins. Recently, several studies have proposed it as the potential gene underlying the QTL on bovine chromosome 6. Hence, in this study, the PCR-SSCP method was applied to detect two polymorphisms (A → C and A → G) in the target sequence coding nucleotide-binding domain (NBD) region of ABCG2 and evaluate its associations with milk production traits and mastitis-related traits among Chinese Holsteins. In the analyzed population, the allelic frequencies for the A and B alleles were 0.5990 and 0.4010, respectively and the genotypic frequencies were in Hardy-Weinberg disequilibrium (P < 0.01). Moreover, significant statistical relationships between the polymorphisms of ABCG2 gene and following traits, including milk yields, milk protein percentage and somatic cell scores (SCS), were found (P < 0.05). When compared with AA genotype, BB genotype was associated with higher milk yields during 1st and 2nd lactations, as well as lower milk protein percentage and SCS. Thus, BB genotype is suggested to be a molecular marker for superior milk performance.

Genetic effects of ABCG2 polymorphism on milk production traits in the Chinese Holstein cattle

“…They also demonstrated that A allele at 45599 position is more frequent in the population. The allele frequency results of our population agree with literature data cited by Yue et al (2010). Such inconsistency may be due to the different population size and family structure of the experimental population.…”

“…Strangely enough, however, the SNP at the g.45599 A !C locus has no significant association with other milk production traits except protein yield and protein percentage in our population, whereas Yue et al (2010) showed significant associations with milk yield and protein percentage in Chinese Holstein cattle. They reported that CC (they named BB at position 45599) genotype was associated with higher milk yields and protein percentage during first and second lactation, indicating allele C was associated with superior milk performance which were in partial agreement with our study.…”

“…They reported that CC (they named BB at position 45599) genotype was associated with higher milk yields and protein percentage during first and second lactation, indicating allele C was associated with superior milk performance which were in partial agreement with our study. Yue et al (2010) identified two novel mutations at position 45599 and 45610 in intron 7. They reported that there was a subtle linkage relationship between the two mutations, and these two mutations give rise to merely two haplotypes (A: A45599 .…”

“…Herein, this is the first report which systematically investigated the genetic effects of ABGC2 gene on milk production traits in Chinese Holstein population. Although Yue et al (2010) reported the same SNP in the Chinese Holstein, they considered only 485 individuals without any genetic relationship, whereas in the current study, a total 2212 animal were considered with tracing back three generations for pedigree information. A total of 31,655 bp in BTA 6 was sequenced by Cohen-Zinder et al (2005) in intergenic, exonic and intronic regions of 10 genes within the critical region of the QTL using DNA of two sires heterozygous for the QTL.…”

“…The effects of SNPs in these genes on the routinely collected traits of milk-fat percentage, milk-fat yield or both have been reported on different cattle populations (Dybus 2002;Brym et al 2004Brym et al , 2005Cohen-Zinder et al 2005;Dybus et al 2005;Weikard et al 2005;Khatib et al 2006;Roy et al 2006;Morris et al 2007). Many individual studies on different dairy cattle population have proposed ABCG2 as the potential gene for milk production underlying the Quantitative Trait Locus (QTL) on bovine chromosome 6, and it is a plausible candidate gene for its putative physiological role on the trait of interest (Wayne & McIntyre 2002;Khatkar et al 2004;Yue et al 2010). ABCG2 especially has a xenotoxin protective function, transfer of xenotoxins from the mother to the suckling infant or young via milk is difficult to reconcile with a protective role.…”