Control of early germline development in C. elegans

项目总结/文摘

Project Summary/Abstract The long-term objective of my research program is to understand how epigenetic information is transmitted across generations and during development. Epigenetic mechanisms enable gene expression and development to be regulated not only by DNA sequence but also by how DNA is packaged into chromatin. The mechanisms for faithfully transmitting information via chromatin packaging or the “epigenome” through DNA replication to daughter cells and from parents to offspring remain mysterious. My lab has developed a powerful model for investigating those mechanisms. In the nematode Caenorhabditis elegans, a set of histone-modifying enzymes enables the parental chromosomes inherited by embryos to transmit an epigenetic “memory of germline” from parent germ cells to the primordial germ cells (PGCs) in offspring. Germ cells that do not inherit that memory die. The key players are MES-4, which marks transcribed regions of the genome with an ON mark (methylation of histone H3 on Lys 36 or H3K36me), and Polycomb Repressive Complex 2 or PRC2, which marks repressed regions of the genome with an OFF mark (H3K27me). Our working hypothesis is that 1) MES-4 and PRC2 mark genomic regions as transcribed (ON) or repressed (OFF) in the parental germline, 2) that pattern of ON and OFF marking is passed to offspring via oocyte and sperm chromatin, and 3) maternally provided MES-4 and PRC2 propagate the pattern through cell divisions to provide the PGCs with proper gene expression “blueprints” for germline development. Our aims test key aspects of this hypothesis. In Aim 1, we will determine if the sperm and oocyte epigenomes each transmit a “memory of germline” to offspring. We will elucidate the distributions of critical histone marks on the sperm and oocyte genomes, the fates of specific sperm and oocyte marking patterns in early embryonic cells, and the consequences of altered sperm or oocyte marking to germline development in offspring. In Aim 2, we will determine how marked and unmarked chromatin states are faithfully propagated through cell divisions by targeted MES-4 and PRC2 action. In Aim 3, we will test if MES-4 and PRC2 marking in parents regulates the transcription program in PGCs, and if altering transcription in the parental germline, by exposing parent worms to environment stresses, leads to altered chromatin marking and transcription patterns in offspring. Epidemiological studies of human populations suggest that what parents experience can affect the physiology, health, and lifespan of their offspring and even grand-offspring. The germline is the conduit between generations. Our studies, which lie at the heart of transgenerational epigenetic inheritance, will provide critical insights into germ cell biology, how chromatin states transmit information from parents to offspring, and how parental experiences may influence the health and longevity of future generations.