We are interested in the mechanisms that regulate the development of the early germline. In Drosophila, germ cell fate is controlled by maternal factors present in the posterior pole plasm (the region of the embryo where the germ cells form). Among these factors is the posterior determinant Nanos, which is required both for abdomen formation and primordial germ cell development (1,2). The C. elegans Sequencing Consortium has identified three genes with homology to Drosophila nanos. Here we show that two of these genes,
nos-1 and
nos-2, are required for the development of the primordial germ cells Z2 and Z3. NOS-1 and NOS-2 are most similar to Drosophila Nanos in a 52 aa region comprising the zinc finger-like motif found in all Nanos-related proteins. Northern and in situ hybridization experiments indicate that
nos-1 and
nos-2 RNAs are transcribed in the adult germline and are present in embryos as maternal RNAs.
nos-1 is also transcribed in the primordial germ cells Z2 and Z3 after the 550-cell stage. During early cleavages,
nos-1 and
nos-2 maternal transcripts are rapidly degraded from somatic lineages, but are maintained in the germ lineage, a pattern typical of many maternal RNAs. However, unlike other maternal RNAs described so far,
nos-2 RNA appears to accumulate on granules in the cytoplasm of germ cells. Double-labeling experiments indicate that the
nos-2 granules coincide with P granules. These results suggest that
nos-2 RNA associates transiently with P granules in germline blastomeres. To determine the function of
nos-1 and
nos-2, we generated embryos lacking
nos-1 and/or
nos-2 activity by RNA-mediated interference (RNAi) (3). Simultaneous injection of
nos-1 and
nos-2 RNAs resulted in sterility in 98% of the F1 progeny. In contrast, 0% of
nos-1(RNAi) and only 30%
nos-2(RNAi) animals were sterile. No embryonic lethality was detected in any combination. To determine the basis of the sterility observed in
nos-1 (RNAi);
nos-2 (RNAi) "double mutants", we stained these animals with P granule antibodies. We found that Z2 and Z3 are formed normally in these animals, but fail to proliferate during larval stages. These results suggest that
nos-1 and
nos-2 function redundantly in the development of primordial germ cells. The "germ-cell-less" phenotype of
nos-1 (RNAi);
nos-2 (RNAi) animals is reminiscent of that observed in Drosophila when nanos function in the germline is analyzed independently from its function in embryonic patterning (2). These results strongly suggest that nanos function in germline development has been conserved in evolution. 1. Kobayashi, S. et al., Nature 380, 708-711 (1996). 2. Forbes, A. and Lehmann, R. Development 125, 679-690 (1998). 3. Fire, A. et al., Nature 391, 806-811 (1998).