Epigenetics and the germline

Abstract

Epigenetic processes affect three stages of germline development, namely (1) specification and formation of primordial germ cells and their germline derivatives through lineage-specific epigenetic modifications, in the same manner as other embryonic lineages are formed, (2) a largely genome-wide erasure and re-establishment of germline-specific epigenetic modifications that only occurs in the embryonic primordial germ cell lineage, followed by re-establishment of sex-specific patterns during gametogenesis, and (3) differential epigenetic modifications to the mature male and female gamete genomes shortly after fertilisation. This review will detail current knowledge of these three processes both at the genome-wide level and at specific imprinted loci. The consequences of epigenetic perturbation are discussed and new in vitro models which may allow further understanding of a difficult developmental period to study, especially in the human, are highlighted.

Genomic imprinting and its relevance to congenital disease, infertility, molar pregnancy and induced pluripotent stem cell

“…We also note that the precise mechanism of imprint establishment may differ between ICRs and, furthermore, there are species differences in factors involved: for example, NLRP7 has not been found in mice, and DNMT3L has not been detected in human oocytes. 102,103 These findings reveal some limitations of mouse studies, despite the great advances made in this tractable model, and underscore the need for additional model systems appropriate for human studies. In this regard, the use of primate species or refinement of the recently developed in vitro germcell production system 104 will be important for future studies.…”

Expression profiles of genes regulating dairy cow fertility: recent findings, ongoing activities and future possibilities

“…Also, DNA methylation allows the silencing of virus-derived and potentially destabilizing repeat sequences that make up large proportions of the mammalian genome (International Human Genome Sequencing Consortium, 2001). Epigenetics determines the formation and specification of germlines, the erasure and re-establishment of methylation patterns in embryonic primordial germ cells and, subsequently, reestablishment of sex-specific patterns during gametogenesis and results in different modifications of the paternal and maternal genome after fertilization (Allegrucci et al, 2005).…”

“…The resulting monoallelic expression of imprinted genes is tissue specific, seems restricted to the prenatal period (Moore, 2001) and functions to limit the production of transcripts (Allegrucci et al, 2005). Imprinted genes may account for only a fraction of the genome (e.g.…”

Epigenetics in development

“…In the late blastocyst, inner cell mass cells reactivate Xp, while extraembryonic cells (trophoectoderm, primitive endoderm) maintain Xp inactivation. Subsequently, the epiblast, or future embryo, initiates random X inactivation (Allegrucci et al, 2005). The mechanisms of imprinted inactivation of Xp and random X inactivation are largely similar; differences are noted below.…”