A crucial process in the development of every multicellular organism is the specification of different developmental fates in different cells of the early embryo. In embryos of the nematode Caenorhabditis elegans, as in embryos of many other species, this process is thought to be controlled mainly by maternally supplied factors that are differentially partitioned during the early divisions of the zygote. In addition to maternal factors, we have new evidence that paternally supplied factors also are required for normal early development. We propose to combine genetic, molecular, and cell biological approaches to identify crucial maternal and paternal factors, learn how lineage-specific factors are differentially partitioned to specific cells, and elucidate when and how such factors participate in cell-fate determination in C. elegans embryos. We have identified a novel paternal effect embryonic lethal mutant, spe- 11, that demonstrates that a sperm-contributed factor is required for normal zygote development. Two exciting possibilities are that the spe- 11 product activates the oocyte or provides polarity to the zygote. To investigate the role of the spe-11 product, we will clone the spe-11 gene and analyze and localize its gene product, define the temperature- sensitive period of the mutant, isolate second site suppressors, and try to rescue mutant zygotes by microinjecting sperm factors. The maternally supplied factors on which we will focus are those required for germ-line development. P granules, which are maternally supplied cytoplasmic structures that are segregated to the germ-line blastomeres during the early divisions, are excellent candidates for germ-line "determinants". We are using biochemcal techniques and our collection of anti-P-granule antibodies to purify and analyze the composition of the granules; our long-term goal is to assess their function in the germ line through genetics. Concurrently, by screening for maternal effect sterile of grand-childless mutants, we are identifying mutants defective in maternal control of germ-line development; some of these may identify the factors that determine the germ line. Finally, we are continuing our analysis of the mechanism of segregation of lineage-specific factors. We have already demonstrated that microfilaments (MFs) play a critical role in the generation of zygotic polarity and in segregating P granules to the germ lineage. We will investigate the role of MFs in partitioning somatic-lineage-specific factors, and we will investigate several specific mechanisms by which MFs could participate in segregation events, such as actin-myosin interactions and cytoplasmic streaming.