As well as genetic information, the egg and sperm also contribute epigenetic annotations that may influence gene activity after fertilisation. These annotations may be direct modifications of the DNA bases or of the proteins around which the DNA is wrapped into chromatin. Our goal is to understand whether, through epigenetics, factors such as a mother’s age or diet have consequences on the health of a child. We examine how epigenetic states are set up in oocytes – or egg cells – and influence gene expression in the embryo. For example, repressive chromatin marks in oocytes lead to long-term silencing of genes inherited from the mother, particularly in cells that will form the placenta. We are also interested in how variations in DNA methylation come about in oocytes and whether we can use this variation as a marker for oocyte quality and embryo potential. To investigate these questions, we develop methods to profile epigenetic information in very small numbers of cells or even in single cells.
In vitro maturation (IVM) of oocytes is a key step in bovine in vitro embryo production, but concerns remain regarding its potential effects on oocyte competence and epigenetic regulation. Information on the DNA methylation profile of bovine oocytes matured in vitro is still limited and inconsistent. In this study, we applied single-cell DNA methylation sequencing to characterise methylation patterns associated with IVM in bovine oocytes. In vivo matured oocytes were included as a biological reference to contextualise methylation landscapes observed following IVM. Eighteen IVM oocytes were collected from abattoir-derived ovaries, and twenty-eight in vivo matured oocytes were obtained by ovum pick-up from Holstein and Braunvieh cows and a Holstein heifer. Single-cell whole-genome bisulfite sequencing was used to assess DNA methylation, and differentially methylated regions (DMRs; FDR < 0.05, FC > 0.1) were identified using the limma package. Genome-wide methylation profiling revealed distinct epigenetic signatures associated with IVM, affecting both gene bodies and regulatory regions. Several differentially methylated regions were linked to genes involved in RNA processing, metabolism, and stress-response pathways relevant to oocyte maturation. IVM oocytes showed lower methylation in CDKN1C and higher methylation in BEGAIN, while SEMA7A, ZNF575, MACROD1, and FGFRL1 were hypomethylated. Comparative analysis further identified a subset of conserved methylation signatures shared between bovine and porcine oocytes, suggesting evolutionary conservation of epigenetic responses to IVM conditions. This study contributes to a deeper understanding of the epigenetic mechanisms underlying oocyte maturation and supports the use of cross-species epigenomic approaches to identify candidate methylation signatures for future validations in studies of oocyte quality and developmental competence.
Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system in which DNA methylation may link genetic and environmental risk factors.
Wnt4 signaling promotes somatic cell development in the female embryo, but its role in germline differentiation during meiosis remains poorly characterized. To explore Wnt4 functions in female embryonic gonads, we isolated germ cells from Wnt4 knock-out mice to investigate histone modifications and DNA methylation distribution patterns. The lack of the Wnt4 signaling pathway deregulates germ cell cycle markers, such as cyclins, alters the cell cycle by impairing meiosis progression, maintains the germ cells in the G1-GO and S phases, and supporting DNMT3A and DNMT1 enzyme expression at meiosis entry. Conversely, in the nucleus of the Wnt4 knock-out female germ cells, an increase of H3K27me3 pattern persists at the entry of meiosis, leading to altered methylation at the Sycp3 promoters combined with an acetylation of Stra8 promoter at E14.5. This changed pattern might be explained by the overexpression of Creb-binding protein (CBP) in the mutant female germ cells, leading to deregulation of histone marks on meiosis genes. Our findings reveal that the Wnt4 signal is necessary for inducing meiosis by inhibiting germ cell proliferation via the regulation of histone modification. Wnt4 signaling plays a crucial role in regulating the delicate balance between DNA methylation and acetylation in female germ cells. This fascinating interaction highlights the complexities of cellular processes that contribute to reproductive health and development.