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Genetics, epigenetics and gene silencing in differentiating mammalian embryos

Abstract

A highly complex pattern of differentiation involving maternal and embryonic factors characterizes the early development of mammalian embryos. These complex genetic and proteonomic patterns of early growth also involve various forms of gene silencing and tissue reprogramming. Understanding the nature of fundamental developmental events is hence essential to appreciate the significance of natural and induced forms of remodelling, damaged forms of gene expression and gene silencing during the initial stages of growth. Natural forms of remodelling include subtle genetic events involved in, for example, the changing nature of imprinting from before fertilization or the inactivation of one X chromosome in female blastocysts. Induced forms include the consequences of nuclear transfer and embryo cloning or the immediate effects of placing embryos in culture media. Animal and human studies are described in this paper, relating reprogramming to detailed embryological and clinical knowledge gained through the use of IVF, preimplantation genetic diagnosis and the establishmentin vitroof stem cells. Attention concentrates on the consequences of variations in all growth stages from the formation of oocytes, through fertilization, the differentiation of blastocysts and early haemopoietic stages in mammalian species. Unique features of gene expression or gene modification are described for each developmental stage.

Keywords: cloning, early embryogenesis, early haemopoietic stages, gene silencing, mammalian embryos, tissue reprogramming.

Footnotes

Editor, Reproductive BioMedicine Online, Duck End Farm, Dry Drayton, Cambridge CB3 8DB, UK.

* Corresponding author.

# Original publication: Edwards, R.G., 2006. Genetics, epigenetics and gene silencing in differentiating mammalian embryos. Reprod. BioMed. Online 13, 732–753.

1 Paper based on contribution presented at the PGDIS Annual Meeting ‘Nuclear transfer and reprogramming’ in Belize, Central America, February 2–5, 2006.