EGO-1 is related to RNA-directed RNA polymerase and functions in germ-linedevelopment and RNA interference in C-elegans

Background: Cell-fate determination requires that cells choose between alte rnative developmental pathways. For example, germ cells in the nematode wor m Caenorhabditis elegans choose between mitotic and meiotic division, and b etween oogenesis and spermatogenesis. Germ-line mitosis depends on a somati c signal that is mediated by a Notch-type signaling pathway. The ego-1 gene was originally identified on the basis of genetic interactions with the re ceptor in this pathway and was also shown to be required for oogenesis. Her e, we provide more insight into the role of ego-1 in germ-line development. Results: We have determined the ego-1 gene structure and the molecular basi s of ego-1 alleles. Putative ego-1 null mutants had multiple, previously un reported defects in germ-line development. The ego-1 transcript was found p redominantly in the germ line. The predicted EGO-1 protein was found to be related to the tomato RNA-directed RNA polymerase (RdRP) and to Neurospora crassa QDE-1, two proteins implicated in post-transcriptional gene silencin g (PTGS). For a number of germ-line-expressed genes, ego-1 mutants were res istant to a form of PTGS called RNA interference. Conclusions: The ego-1 gene is the first example of a gene encoding an RdRP -related protein with an essential developmental function. The ego-1 gene i s also required for a robust response to RNA interference by certain genes. Hence, a protein required for germ-line development in C. elegans may be a component of the RNA interference/PTGS machinery.