Abstract
ObjectiveAn initial RNA-Sequencing study revealed that UDP-galactose-4-epimerase (GALE) was one of the most promising candidates for milk protein concentration in Chinese Holstein cattle. This enzyme catalyzes the interconversion of UDP-galactose and UDP-glucose, an important step in galactose catabolism. To further validate the genetic effect of GALE on milk protein traits, genetic variations were identified, and genotypes-phenotypes associations were performed.MethodsThe entire coding region and the 5′-regulatory region (5′-UTR) of GALE were re-sequenced using pooled DNA of 17 unrelated sires. Association studies for five milk production traits were performed using a mixed linear animal model with a population encompassing 1,027 Chinese Holstein cows.ResultsA total of three variants in GALE were identified, including two novel variants (g.2114 A>G and g.2037 G>A) in the 5′-UTR and one previously reported variant (g.3836 G>C) in an intron. All three single nucleotide polymorphisms (SNPs) were associated with milk yield (p<0.0001), fat yield (p = 0.0006 to <0.0001), protein yield (p = 0.0232 to <0.0001) and protein percentage (p<0.0001), while no significant associations were detected between the SNPs and fat percentage. A strong linkage disequilibrium (D’ = 0.96 to 1.00) was observed among all three SNPs, and a 5 Kb haplotype block involving three main haplotypes with GAG, AGC, and AGG was formed. The results of haplotype association analyses were consistent with the results of single locus association analysis (p<0.0001). The phenotypic variance ratio above 3.00% was observed for milk protein yield that was explained by SNP-g.3836G >C.ConclusionOverall, our findings provided new insights into the polymorphic variations in bovine GALE gene and their associations with milk protein concentration. The data indicate their potential uses for marker-assisted breeding or genetic selection schemes.
Highlights
Milk proteins are important nutrients and milk protein concentration serves as valuable index for milk quality
Strong interactions were observed between GALE and several other genes such as lactalbumin, alpha (LALBA), beta 1,4galactosyltransferase, polypeptide 1 (B4GALT1), and UDPglucose 6-dehydrogenase (UGDH) that play important roles in milk composition synthesis (Supplementary Figure S1) [8,9,10]
Genetic sampling A total of 1,027 Chinese Holstein cows and their 17 corresponding sires were considered as the study population
Summary
Milk proteins are important nutrients and milk protein concentration serves as valuable index for milk quality. With the development of genomics, bioinformatics and statistical genetics, a single gene or chromosome segments affecting important economic traits can be analyzed [2]. It is possible to improve milk protein concentration through marker assisted selection (MAS) or genomic selection schemes, the challenge, is to identify key genes or causal variations affecting milk protein traits [3,4,5,6]. Based on the biological function and trans criptional effects on milk protein traits, the current study mined to screen the full-length coding regions of the GALE gene for single nucleotide polymorphisms (SNPs) and to evaluate the genetic effects of polymorphisms on milk production traits in a large Chinese Holstein population
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