The germ lineage is the guardian of the genome and gatekeeper of the genetic, and epigenetic, information that is passed between generations. An essential characteristic of germ cells is their underlying totipotency: the inherent capacity to generate all tissues. Totipotency is an epigenetic characteristic-- processes that affect the epigenetic content of the germ line genome not only have the potential to affect germ line and somatic development within an individual, but can also affect developmental processes in subsequent generations. Our long-term goal is to understand the epigenetic processes that operate during the germ cell cycle within and between generations: i.e., how is heritable epigenetic content is established, how is it recognized and interpreted, and how is it reprogrammed as the germ line progresses through each stage? My lab has been at the forefront of establishing the nematode C. elegans as an exceptional model for studying these processes, as it possesses numerous genetic and molecular strengths that make both intra- and trans-generational studies of the germ line cycle feasible. Furthermore, the process of germ cell specification in C. elegans is remarkably similar to specification in mammals. These include a mixed soma/germline/embryonic stem cell (ESC)-like phase, a prolonged G2-stage cell cycle arrest, genome-wide epigenetic reprogramming, and transient specialized regulation of RNA Pol II. Indeed, observations made in C. elegans have stimulated the investigations in mammals that have cemented these similarities. One of these similarities is the focus of the proposed research: the unique regulation of RNA Pol II during primordial germ cell (PGC) specification. In many animals, including worms, flies, frogs, and mice, there is a period of RNA Pol II inactivity that accompanies PGC specification. In all species this is observed as the absence of the elongating RNA Pol II phospho-epitope, Ser2P. We have recently shown that in C. elegans, there is a curious appearance of Ser2P at PGC specification that is transient and regulated by kinases in a manner distinct from the surrounding somatic cells. Such regulation may contribute to, or be a special characteristic of, germ line totipotency as reports suggest Ser2P shows unique regulation in pluripotent stem cells. We are poised to identify the mechanisms that regulate Pol II during PGC specification, identify its genomic distribution in the nascent PGCs, and identify the transcriptome that may contribute to the functions of early and post-embryonic germ cell development. This will yield important insights into conserved aspects of germ cell development, and provide further paradigms for similar investigations in mammals. Given the absolute importance of the germ line for both trans-generational genome protection and epigenetic modes of inheritance, these studies are highly significant as they will inform how these processes proceed normally, and why when disrupted they lead to human congenital and fertility defects.
The proposed research is highly relevant to public health, as it focuses on epigenetic mechanisms that affect the genome in the germ line, and thus mechanisms that can contribute to heritable forms of human disease. These studies also impact the nascent realization that epigenetic errors can lead to trans-generational defects. They are therefore relevant to NIH's mission to develop fundamental understanding the causes of human disease states, and ultimately reduce the burdens of human developmental defects, human sterility, and resulting disabilities.
