Controlling gene expression in vivo involves regulating multiple hierarchies of protein complexes and their association with DNA. The sequential control of gene expression during embryogenesis has evolved to yield many variations of similar themes, with details that are specific to each species. In most metazoan animals, only the germ cells retain, throughout both development and successive generations, the ability to renew an entire organism. Germ cells therefore retain totipotency. The retention of totipotency appears to be accomplished in many animals, at least in part, by an orchestrated sequestration of the primordial germ cells, coupled with an inherent unresponsiveness to most developmental cues. Using the nematode Caenorhabditis elegans as a model system, a combination of genetic and molecular approaches will be used to investigate the processes that confer and maintain germ cell totipotency. One candidate process is genetic silencing of chromatin. This epigenetic process has components that are germ cell specific; these components likely participate in the maintenance of germ cell identity. The genetics available in C. elegans will be used to create and isolate mutations that cause defects in germ line silencing. The mutations will be characterized and the defective genes will be identified. The role of these genes in chromatin organization will be investigated using a variety of probes to assess the mutants' effects on nucleosomal histone modifications and chromosomal interactions during meiosis. How the different components interact to orchestrate the silencing process will also be determined. It is hoped that an understanding of these processes in the germ lineage will provide an understanding of the underlying mechanisms that are common to all descendents of this founding lineage.