Now showing 1 - 2 of 2
  • Publication
    Epigenetic processes in the male germline
    (CSIRO Publishing, 2014-09) ;
    Sperm undergo some of the most extensive chromatin modifications seen in mammalian biology. During male germline development, paternal DNA methylation marks are erased and established on a global scale through waves of demethylation and de novo methylation. As spermatogenesis progresses, the majority of the histones are removed and replaced by protamines, enabling a tighter packaging of the DNA and transcriptional shutdown. Following fertilisation, the paternal genome is rapidly reactivated, actively demethylated, the protamines are replaced with histones and the embryonic genome is activated. The development of new assays, made possible by high-throughput sequencing technology, has resulted in the revisiting of what was considered settled science regarding the state of DNA packaging in mammalian spermatozoa. Researchers have discovered that not all histones are replaced by protamines and, in certain experiments, various species of RNA have been detected in what was previously considered transcriptionally quiescent spermatozoa. Most controversially, several groups have suggested that environmental modifications of the epigenetic state of spermatozoa may operate as a non-DNA-based form of inheritance, a process known as 'transgenerational epigenetic inheritance'. Other developments in the field include the increased focus on the involvement of short RNAs, such as microRNAs, long non-coding RNAs and piwi-interacting RNAs. There has also been an accumulation of evidence illustrating associations between defects in sperm DNA packaging and disease and fertility. In this paper we review the literature, recent findings and areas of controversy associated with epigenetic processes in the male germline, focusing on DNA methylation dynamics, non-coding RNAs, the biology of sperm chromatin packaging and transgenerational inheritance.
      947ScopusĀ© Citations 25
  • Publication
    Intragenic sequences in the trophectoderm harbour the greatest proportion of methylation errors in day 17 bovine conceptuses generated using assisted reproductive technologies
    Background: Assisted reproductive technologies (ART) are widely used to treat fertility issues in humans and for the production of embryos in mammalian livestock. The use of these techniques, however, is not without consequence as they are often associated with inauspicious pre- and postnatal outcomes including premature birth, intrauterine growth restriction and increased incidence of epigenetic disorders in human and large offspring syndrome in cattle. Here, global DNA methylation profiles in the trophectoderm and embryonic discs of in vitro produced (IVP), superovulation-derived (SOV) and unstimulated, synchronised control day 17 bovine conceptuses (herein referred to as AI) were interrogated using the EmbryoGENE DNA Methylation Array (EDMA). Pyrosequencing was used to validate four loci identified as differentially methylated on the array and to assess the differentially methylated regions (DMRs) of six imprinted genes in these conceptuses. The impact of embryo-production induced DNA methylation aberrations was determined using Ingenuity Pathway Analysis, shedding light on the potential functional consequences of these differences. Results: Of the total number of differentially methylated loci identified (3140) 77.3 and 22.7% were attributable to SOV and IVP, respectively. Differential methylation was most prominent at intragenic sequences within the trophectoderm of IVP and SOV-derived conceptuses, almost a third (30.8%) of the differentially methylated loci mapped to intragenic regions. Very few differentially methylated loci were detected in embryonic discs (ED); 0.16 and 4.9% of the differentially methylated loci were located in the ED of SOV-derived and IVP conceptuses, respectively. The overall effects of SOV and IVP on the direction of methylation changes were associated with increased methylation; 70.6% of the differentially methylated loci in SOV-derived conceptuses and 57.9% of the loci in IVP-derived conceptuses were more methylated compared to AI-conceptuses. Ontology analysis of probes associated with intragenic sequences suggests enrichment for terms associated with cancer, cell morphology and growth. Conclusion: By examining (1) the effects of superovulation and (2) the effects of an in vitro system (oocyte maturation, fertilisation and embryo culture) we have identified that the assisted reproduction process of superovulation alone has the largest impact on the DNA methylome of subsequent embryos.
      238ScopusĀ© Citations 11