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Based on our results of genome-wide association analysis, we performed gene ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis; three candidate genes (ABCG2, CD44, SPP1) were screened in this study for SNPs association analysis with production traits in 999 Holstein cattle. In this research, flight mass spectrometry genotyping was used to detect the polymorphism of SNP seats. It was shown that four, four, and two single nucleotide polymorphisms (SNP) loci were detected for the ABCG2, CD44, and SPP1 genes, respectively, and the different genotypes of these 10 SNPs significantly affected the milk production performance of Chinese Holstein cattle in terms of milk yield, milk fat percentage, milk protein percentage, somatic cell score, and urea nitrogen content. Among them, ABCG2-G.80952G > T locus, ABCG2-G.120017G > A locus and CD44-G.2294G > C locus had significant effects on somatic cell score (p < 0.01). Cows with GG genotypes at ABCG2-G.80952G > T locus, AA and GG genotypes at ABCG2-G.120017G > A locus, and GG genotypes at CD44-G.2294G > C locus had lower somatic cell scores. The present study elucidated that ABCG2, CD44, and SPP1 could be selected for marker-assisted selection and will benefit for future precise molecular breeding.

Meat quality and meat composition are not separated from the influences of animal genetic improvement systems; the growth and development of skeletal muscle are the primary factors in agricultural meat production and meat quality. Though the muscle-type cofilin (CFL2) gene has a crucial influence on skeletal muscle fibers and other related functions, the epigenetic modification mechanism of the CFL2 gene regulating meat quality remains elusive. After exploring the spatiotemporal expression data of CFL2 gene in a group of samples from fetal bovine, calf, and adult cattle, we found that the level of CFL2 gene in muscle tissues increased obviously with cattle age, whereas DNA methylation levels of CFL2 gene in muscle tissues decreased significantly along with cattle age by BSP and COBRA, although DNA methylation levels and mRNA expression levels basically showed an opposite trend. In cell experiments, we found that bta-miR-183 could suppress primary bovine myoblast differentiation by negatively regulated CFL2. In addition, we packaged recombinant adenovirus vectors for CFL2 gene knockout and overexpression and found that the CFL2 gene could promote the differentiation of primary bovine myoblasts by regulating marker genes MYOD, MYOG and MYH3. Therefore, CFL2 is an essential mediator for promoting myogenic differentiation by regulating myogenic marker genes in cattle myoblasts.

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Agricultural meat composition and quality are not independent of the effects of skeletal muscle growth and development in animals. Cofilin is distributed extensively in muscle and non-muscle cells, and its function is tightly regulated in the cell. Cofilin has two variants in mammals, cofilin-1 (CFL1, non-muscle type) and cofilin-2 (CFL2, muscle type), and has a dual function on skeletal muscle fibers. Our study examined the expression pattern of CFL1 and CFL2 in different fetal bovine, calf, and adult cattle tissues. The content of the CFL2 gene increased significantly with the increase in cattle age in muscle tissues; CFL1 showed the opposite trend. In muscle tissues, DNA methylation levels of CFL1 and CFL2 were high in fetal bovine, and the mRNA level of CFL2 was significantly lower compared to CFL1. However, DNA methylation levels of CFL2 were lower than CFL1, and the mRNA level of CFL2 was remarkably higher compared to CFL1 in adult cattle. Overexpression of CFL1 or knockdown CFL2 reduced the expression levels of muscle differentiation markers, i.e., MYOD, MYOG, and MYH3. Overexpression of CFL2 or knockdown CFL1 stimulated the expression of these marker genes. Therefore, CFL2 may be superior to CFL1 as a candidate gene for subsequent research on cattle genetics and breeding.