Epigenetic Aspects of Fertilization and Preimplantation Development in Mammals: Lessons from the Mouse

Abstract

During gametogenesis, the parental genomes are separated and are epigenetically marked by modifications that will direct the expression profile of genes necessary for meiosis as well as for the formation of the oocyte and sperm cell. Immediately after sperm-egg fusion, the parental haploid genomes show great epigenetic asymmetry with differences in the levels of DNA methylation and histone tail modifications. The epigenetic program acquired during oogenesis and spermatogenesis must be reset for the zygote to successfully proceed through preimplantation development and this occurs as the two genomes approach each other in preparation for karyogamy. During preimplantation development, the embryo is vested with the responsibility of maintaining the primary imprints. In addition, female embryos must silence one of the X-chromosomes in order to transcribe equal levels of X-linked genes as their male counterparts. This review is intended as a survey of the epigenetic modifications and mechanisms present in zygotes and preimplantation mouse embryos, namely DNA methylation, histone modifications, dosage compensation, genomic imprinting, and regulation by non-coding RNAs.

KEYWORDS:

• DNA methylation
• embryos
• epigenetics
• gametes
• histones

ACKNOWLEDGMENTS

The author apologizes for any relevant research that was omitted. Also, the author wishes to thank Mrs. Sarah Huffman for assistance with the preparation of this manuscript.

Declaration of Interest: The author reports no conflicts of interest. The author alone is responsible for the content and writing of the paper.