Environmentally Induced Epigenetic Transgenerational Inheritance in Fish and Mammals Female Reproduction

Abstract

Epigenetic modifications control how genetic information is expressed without altering genetic codes stored in DNA. Environmental exposures can positively or negatively influence epigenetic modifications, leading to alterations in physiological functions. Some exposure-induced epigenetic alterations (epimutations) can be passed down to subsequent generations through non-genetic inheritance. Both in mammals and fish, inter and transgenerational reproductive impairments occur due to exposure to various environmental chemicals, leading to impaired offspring׳s reproductive and metabolic health in subsequent generations. Transgenerational passage of reproductive phenotype can persist for several generations if induced epimutations in germ cells are resistant to the reprogramming barrier. The organism can remove exposure-induced gametically transmitted epimutations in somatic cells during the post-fertilization and pre-implantation stages of embryonic development and germ cells during phenotypic sex determination of gonads. If the epigenome fails to erase epimutations during the natural epigenomic reprogramming process, they can be transferred by the germ line to the somatic cells of subsequent generations as epigenetic memories. The epigenetic memory in cells can be carried in CpG sites and islands (CGI) of the genome and maintained by DNA methyltransferases. Heritable differential DNA methylation profile, often called epimutations, on CGIs undergoes erasure in primordial germ cells (PGCs) and is subsequently reestablished in post-implantation embryos through the proceess of epigenetic reprogramming of epigenome. Such heritable epimutations may be deleterious for the organism’s health if not corrected by endogenous epigenetic reprogramming mechanisms. It is, therefore, important to understand how the environment interacts with the genome and how this interaction can be inhibited. In case the interaction occurs, it is important to block or deviate pathways to the disease before its onset or progression. This chapter reviews the literature on the mechanisms of epigenetic inheritance and associated reproductive health impairments in female fish and mammals.