The transcriptome that defines a differentiated cell type is strongly influenced by the chromatin structure imposed on the genome by epigenetic processes. This structural information becomes heritably stabilized, or programmed, as differentiation proceeds through the cell divisions required to build a tissue. The stability of ths information is revealed by the difficulties encountered when trying to reverse, or reprogram, a differentiated cell into a pluripotent stem cell state. Current strategies, such as induced pluripotent stem cell (iPS) technologies are amazing but inefficient, and the quality of the cells obtained is unclear. These problems are due the stochastic nature of uncontrolled processes involved in these reprogramming techniques. In contrast, the highly differentiated gamete genomes are quite efficiently and accurately reprogrammed when they meet in the zygote, creating a totipotent epigenome. Importantly, there is epigenetic information that arrives in the gametes, encoded in the parental germ line, which is not targeted for reprogramming. This information presumably contributes to the totipotency of the zygote and the continued immortality of the germline. Three questions are central to understanding these processes: 1) How is epigenetic information inherited through the gametes reprogrammed in the zygote?;2) How does specific information avoid this fate to remain stable through generations?;and 3) How is discrimination between the appropriate targets for these different fates achieved? In this project, we will take advantage of the genetic and epigenetic tools available in C. elegans to identify targets of zygotic reprogramming. We will further identify epigenetic modifiers that participate in the parental programming and zygotic reprogramming mechanisms. We will test and adapt protocols to expand the analyses to a genome-wide approach. The longer-term goal is to use the information obtained by these experiments to identify the mechanisms that direct the programming and reprogramming machinery to the appropriate sites in the genome. This will ultimately guide therapies to interrupt or manipulate mechanisms that contribute to heritable epigenetic disease states, and identify strategies that will appropriately guide in vitro reprogramming to efficiently achieve a state compatible with therapeutic safety.
The genetic information that is passed from parent to child is accompanied by epigenetic information that can affect how genes behave in the offspring. Epigenetic information is encoded within the parental germline and packaged into the gametes. Some of this information is reprogrammed in the offspring when the gametes meet at fertilization;however, some of the encoded information is not reprogrammed and may contribute to totipotency-the ability of the fertilized egg to generate all tissues arising during embryonic development. We are working to understand the nature of this encoding process in the parent. We are also determining how some encoded information is reprogrammed in the embryo but other information remains heritable across many generations, and how discrimination between these classes of information is achieved.
| Grossniklaus, Ueli; Kelly, William G; Kelly, Bill et al. (2013) Transgenerational epigenetic inheritance: how important is it? Nat Rev Genet 14:228-35 |
