Scientists Uncover How Marine Invertebrates Bypass Mammalian Epigenetic Rules

Typically, the information encoded in DNA allows organisms to develop, function and pass traits across generations. Yet DNA alone does not explain how genes are switched on and off in different cells and environments. This regulation is partly controlled by other factors called epigenetics, such as DNA methylation, a chemical modification that can influence gene activity without changing the genetic code itself. 

In mammals, most epigenetic information is erased after fertilization (when the sperm and egg fuse), preventing the widespread inheritance of acquired epigenetic states between generations. However, this type of resetting appears to be absent in the invertebrate animals, such as worms, corals, sea anemones or sea urchins. 

In this study, the scientists experimentally removed DNA methylation in a sea anemone (Nematostella vectensis) to test what happens when these epigenetic patterns are disrupted. Surprisingly, animals developed normally despite losing most of their DNA methylation. Rather than causing major defects in gene regulation, methylation loss mainly unleashed hidden "jumping genes" or "selfish genes", embedded within active genes. If left unchecked, these genetic parasites can insert themselves into important genes and regulatory regions, potentially disrupting normal development and threatening genome stability. 

Because these animals lack the extensive epigenetic resetting that occurs after fertilization in mammals, some abnormal methylation states persisted in the offspring. These inherited epigenetic changes altered how genes are switched on in the next generation, demonstrating that experimentally induced epigenetic variation can be transmitted across generations in an animal."

Dr. Alex de Mendoza, Queen Mary University of London

The findings suggest that the ancestral role of DNA methylation in animals was not primarily to regulate gene expression, but to protect active genes from disruptive jumping genes. In mammals, this same molecular system has since been recruited for a wide range of functions, including regulating development and silencing one of the two X chromosomes in females. The study therefore provides a glimpse into the evolutionary origins of important regulatory systems. Moreover, the work also reveals how incomplete epigenetic resetting can allow heritable variation to persist across generations without requiring genetic changes, providing potential raw material for evolutionary change. This work shows how more ancient systems of gene regulation can transmit information through generations.