This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The genome—which contains genes encoded in DNA—acts as the fundamental blueprint of life. But what you might not know is that, in addition to this genetic information, we have something akin to an "instruction manual" for how genes should be handled.
This instruction manual is known as the epigenome. Azusa Inoue, team director of the Laboratory for Epigenome Inheritance at the RIKEN Center for Integrative Medical Science, is investigating how the epigenome behaves during the creation of egg cells, or oocytes. Recent studies have revealed that the epigenome of the oocyte plays important roles in the development of the fetus and placenta following fertilization, as well as in maintaining pregnancy.
The latest findings are published in the journal Molecular Cell. RIKEN spoke with Inoue about this "wisdom of life"—knowledge encoded in the epigenome that may help us understand how organisms develop from birth through growth and aging. The concept of the epigenome was proposed in the 1940s to solve a fundamental problem in development: How can a single fertilized egg, containing essentially the same genetic information in every descendant cell, develop into an organism containing many radically different kinds of cells?
The prefix epi- means "upon" or "in addition to" and is used to refer to information added to the genetic information encoded in the genome. This information takes the form of chemical modifications attached to DNA or to proteins associated with DNA. Epigenetics has attracted considerable attention as a field of research with potential applications in understanding disease mechanisms and developing new therapies and drugs.
"Originally, I wanted to understand how a huge and complex organism could develop from a single cell—the fertilized egg," Inoue says. The cells that make up our bodies include many specialized cell types—neurons and muscle cells, for example—which differentiate based on the blueprint coded in DNA. Yet when two highly differentiated germ cells, typically an oocyte and a sperm, fuse at fertilization to form a zygote—the single cell that becomes the organism—the resulting cell acquires totipotency, the ability to differentiate into any cell type.
For this to happen, some form of "resetting" must occur. It was once thought that the epigenomes of both the oocyte and sperm would likewise be reset. "Both the oocyte and sperm undergo epigenetic reprogramming after fertilization, but they are not completely reset to a blank slate.
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