Differential promoter methylation of DAZL gene in bulls with varying seminal parameters

DNA methylation studies in cattle

Investigation of the role of epigenetics in cattle breeding is gaining importance. DNA methylation represents an epigenetic modification which is essential for genomic stability and maintenance of development. Recently, DNA methylation research in cattle has intensified. The studies focus on the definition of methylomes in various organs and tissues in relation to the expression of genes underlying economically important traits, and explore methylome changes under developmental, environmental, disease, and diet influences. The investigations further characterize the methylation patterns of gametes in connection with their quality, and study methylome alterations in the developing naturally or assisted produced zygotes, embryos, and fetuses, considering their viability. A wide array of technologies developed for accurate and precise analysis of DNA methylation patterns is employed for both single-gene and genome-wide studies. Overall, the research is directed towards the identification of single methylation markers or their combinations which may be useful in the selection and breeding of animals to ensure cattle improvement.

DNA methylation in bull spermatozoa: evolutionary impacts, interindividual variability, and contribution to the embryo

The DNA methylome of spermatozoa results from a unique epigenetic reprogramming crucial for chromatin compaction and the protection of the paternal genetic heritage. Although bull semen is widely used for artificial insemination (AI), little is known about the sperm epigenome in cattle. The purpose of this review is to synthetize recent work on the bull sperm methylome in light of the knowledge accumulated in humans and model species. We will address sperm-specific DNA methylation features and their potential evolutionary impacts, with particular emphasis on hypomethylated regions and repetitive elements. We will review recent examples of interindividual variability and intra-individual plasticity of the bull sperm methylome as related to fertility and age, respectively. Finally, we will address paternal methylome reprogramming after fertilization, as well as the mechanisms potentially involved in epigenetic inheritance, and provide some examples of disturbances that alter the dynamics of reprogramming in cattle. Because the selection of AI bulls is closely based on their genotypes, we will also discuss the complex interplay between sequence polymorphism and DNA methylation, which represents both a difficulty in addressing the role of DNA methylation in shaping phenotypes and an opportunity to better understand genome plasticity.

Promoter DNA methylation and expression analysis of PIWIL1 gene in purebred and crossbred cattle bulls

Major credit for India being the largest producer of milk in the world, goes to crossbred cows produced by inseminating low-producing indigenous cattle with semen from high producing exotic bulls. However, over the years, the policy of crossbreeding has been confronted with a major problem of subfertility in crossbred male progenies, culminating into disposal of a major fraction of mature bulls. Many studies have demonstrated relationship between epigenetic alterations and male fertility across different species. PIWIL1 is an important candidate gene for spermatogenesis and germ line development. Negative correlation between DNA methylation and expression of this gene has been highlighted in inter species hybrids of cattle and yaks. The present study envisaged elucidating promoter methylation status and expression profile of PIWIL1 gene in exotic Holstein Friesian cattle, indigenous Sahiwal cattle and their crossbreds with varying semen motility parameters. Semen samples were collected from bulls for isolation of DNA and RNA from spermatozoa. Bisulfite converted DNA was used to amplify promoter of PIWIL1 gene using methylation specific primers. The amplified products were sequenced after cloning in pTZ57R/ T vector. The degree of methylation of the PIWIL1 promoter region was significantly higher in poor motility crossbred bulls (7.17%) as compared to good motility crossbreds (1.02%), Sahiwal (1.02%) and Holstein Friesian bulls (0.77%). PIWIL1 expression was 1.75, 1.71 and 1.59 folds higher in HF, Sahiwal and good motility crossbreds, respectively as compared to poor motility crossbreds.

DNA methylation pattern of the goat PITX1 gene and its effects on milk performance

Paired-like homeodomain transcription factor 1 (PITX1) is a pivotal gene in the hypothalamic–pituitary–adrenal axis, which is a well-known pathway affecting lactation performance. The aim of this study was to analyze the DNA methylation profile of the PITX1 gene and its relevance to milk performance in Xinong Saanen dairy goats; thus, potential epigenetic markers of lactation performance were identified. A total of 267 goat blood samples were divided into “low” and “high” groups according to two milk traits: the average milk yield (AMY) and the average milk density (AMD). One CpG island in the 3′-flanking region of the PITX1 gene was identified as being related to milk performance. Fisher's exact test demonstrated that the methylation rates of the overall CpG island and the 3rd and 12th CpG-dinucleotide loci in the blood were significantly associated with the AMY, and the overall methylation rate of the high AMY group was relative hypomethylation compared with the low AMY group. The overall methylation rates of this CpG island in mammary gland tissue from dry and lactation periods again exhibited a significant difference: the lactation period showed relative hypomethylation compared with the dry period. Bioinformatic transcription factor binding site prediction identified some lactation performance related transcription factors in this CpG island, such as CTCF, STAT, SMAD, CDEF, SP1, and KLFS. Briefly, overall methylation changes of the CpG island in the PITX1 gene are relevant to lactation performance, which will be valuable for future studies and epigenetic marker-assisted selection (eMAS) in the breeding of goats with respect to lactation performance.

Promoter methylation and expression analysis of Bvh gene in bulls with varying semen motility parameters

Crossbreds of low-producing indigenous cattle and high-producing exotic dairy bulls (Holstein Friesian and Jersey) have contributed in ensuring that India continues to be the world's top milk-producing country. However, subfertility observed in crossbred male progenies has been a major obstacle in exploitation of heterosis due to crossbreeding. There is sufficient scientific evidence in support of genetic and epigenetic regulation of key physiological processes including spermatogenesis. Bovine Vasa Homology (Bvh) is considered a molecular marker for the study of gametogenesis. Significant negative correlation between DNA methylation and gene expression has been reported in cattle-yaks hybrids and their parents. The present study analyzed promoter methylation status and expression profile of Bvh gene in spermatozoa from exotic Holstein Friesian cattle, indigenous Sahiwal cattle and their crossbreds with varying semen motility parameters. The degree of methylation of the Bvh promoter region was significantly higher in poor motility crossbred bulls (13.3%) as compared to good motility crossbreds (5.3%), Sahiwal (3%) and Holstein Friesian bulls (1%) (P < 0.05). Gene expression analysis revealed significantly higher mRNA abundance of Bvh in purebreds (Holstein Friesian and Sahiwal) as compared to crossbred counterparts (P < 0.001). Inverse correlation observed in this study between promoter methylation and gene expression of Bvh gene in spermatozoa from crossbred bulls with poor motility phenotype as compared to purebred parents provides an important insight into understanding the graded fertility of crossbred bulls.