Mammary gland-specific hypomethylation ofHpa II sites flanking the bovine αS1-casein gene

Abstract

In the lactating cow, mammary gland-specific hypomethylation occurs at two Hpa II sites in the 5'-flanking region of the alpha S1-casein gene, and one in the 3'-region. These sites, A, B and C, are at nucleotide position -1388, -774 and +18034, respectively, relative to the major transcription start site. Site B was hypomethylated when the alpha S1-casein gene was expressed, and methylated when not expressed. In transgenic mice containing the bovine alpha S1-casein 5' and 3' regulatory elements fused to the human lactoferrin (hLF) cDNA, in some cases similar methylation patterns of sites A and B, as compared to the situation in the cow, were observed. In five mouse lines (out of the seven analysed) expressing the transgene in the milk, site B was hypomethylated in the mammary gland, while it was methylated in liver. In the two other mouse lines, no correlation was found between transgene expression and mammary gland-specific hypomethylation of site B. One of the five mouse lines with transgene expression and showing mammary-gland-specific hypomethylation of site B was studied in detail. In this mouse line, induction of transgene expression preceded hypomethylation of site B.

Milk’s Role as an Epigenetic Regulator in Health and Disease

“…It is of critical importance to realize that DNA demethylation of lactation-specific genes is a critical regulatory mechanism that increases gene expression for milk protein and lipid synthesis. In the lactating cow, mammary gland-specific hypomethylation of the αS1-casein gene increased casein expression [115]. Hypomethylation of casein genes during lactation have also been demonstrated in other species [113].…”

DNA-remethylation around a STAT5-binding enhancer in the αS1-casein promoter is associated with abrupt shutdown of αS1-casein synthesis during acute mastitis

“…However, considering the function-specific modulation of the methylation around the remote CoRE area as a paradigm for the entire gene, we would envisage that lactation-specific demethylation occurs also at other CpG dinucleotides dispersed over the gene. Indeed, function-associated demethylation of a proximal CpG dinucleotide in the bovine aS1-casein promoter (at position K774) has been observed during the analyses of transgenic mice lines, expressing a bovine aS1-casein promoter-driven lactoferrin-encoding transgene (Platenburg et al 1996). Unclear, however, remains the significance of the observed increased percentage of methylated aS1-promoter molecules in the udders of these cows, which had given birth to calves but had never been milked.…”

DNA Methylation and Transcription in a Distal Region Upstream from the Bovine AlphaS1 Casein Gene after Once or Twice Daily Milking

“…These CSN genes, some of which are really close to each other, have been shown to be globally co-regulated in both mice and cattle [9]–[11] and to reach maximum levels of expression during lactation. Their regulatory regions, and the epigenetic marks which control gene expression at different physiological stages in vivo or in vitro , have been analysed [4], [12]–[14]. However, regions which allow the specific expression of CSN genes in the mammary gland, as opposed to those of HSTN, STATH and ODAM which are also detected in other tissues, have yet to be defined.…”

“…In the mammary gland of non-lactating heifers and lactating cows, both proximal (−1.4 kb down to −700 nt) and distal (−10.4 kb down to −9.9 kb) upstream regulatory regions of the bovine CSN1S1 gene have been shown to be methylated [4], [12] to lower levels, than the liver which will never express the gene. Furthermore, inflammation induced by mastitis has been shown to reduce CSN1S1 expression and increase the DNA methylation of three CpG located within a distal upstream regulatory region of the gene (Figure 1B and 1C) [4].…”