The goal is to understand the mechanisms by which cells become committed to specific developmental fates in early embryogenesis. Using embryos of the nematode Caenorhabditis elegans, and taking a combined genetic, cellular, and molecular approach, we shall continue to investigate the nature of early cytoplasmic influences on cell fate. We plan to test the validity of two possible models for the mechanism of determination. Model A is the classical view that several distinct, lineage-specific, maternally derived cytoplasmic deteminants in the form of informational macromolecules are segregated during cleavage to the various embryonic founder cells, whose fates are thereby determined prior to the onset of embryonic gene expression. Model B is an alternative view that gradients of only one or two less specific, maternally derived determinants dictate these fates by regulating early differential expression of selector genes in the different founder cells. In evaluating Model A, we shall biochemically and functionally characterize the germ-line-specific P granules, which segregate in the manner of cytoplasmic determinants, to establish whether or not they are, in fact, determinative for the germ line. Biochemical characterization will include analysis of their components by immunoprecipitation and islolation of cloned genes coding for the major P-granule antigens. Experiments to ascertain their function(s) will include microinjection of anti-P-granule antibodies into early embryos and continued screening for P-granule-defective mutants. To evaluate Model B we shall characterize the earliest embryonic gene expression after fertilization, by radioactive labelling of RNA in early embryos as well as generation of monoclonal antibodies against the first newly synthesized embryonic antigens. As byproducts of these experiments we hope to expand our library of monoclonal antibodies to lineage-specific antigens and to identify additional components of the cellular machinery responsible for generating asymmetry and for accomplishing asymmetric segregation in the early embryo.
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