ABSTRACT
INTRODUCTION Both genetic and epigenetic information are passed on from one generation to the next, and it is the germ cells, the precursors to eggs and sperm, that provide this link between generations. While genetic information is transmitted in the form of DNA, epigenetic information is saved in the form of DNA modifications that do not alter the DNA sequence. To date, three main types of epigenetic mechanisms are known to exist, including (i) DNA methylation, (ii) RNAmediated silencing, and (iii) histone modifications. However, DNA methylation is the predominant mechanism studied to date. Two waves of DNA methylation erasure and subsequent de novo DNA methylation occur during the life of an individual. The first wave of methylation erasure takes place during early embryo development, and methylation is subsequently reestablished in a wave of de novo methylation at the time of implantation (1). The second wave of DNA methylation erasure solely affects primordial germ cells (PGCs) and prevents epimutations from being passed on to the next generation.
