Unlike unicellular organisms which always grow to a certain size and then divide, the cells of metazoans sometimes grow without dividing and at other times in development divide without growing. We have characterized a gene, ncl-1, that represses both the synthesis of ribosomes and the size of cells in the animal. Mutations in the ncl-1 gene were identified because most of the cells contain enlarged nucleoli. While the number of cells is not changed in the mutants, the cells are bigger and the animals are bigger than wild type. The ncl-1 gene encodes a protein with motifs common to several genes which when mutated cause cancer in mammals.
Germ cells contain material in the cytoplasm called germ plasm.
Many experiments indicate that this material constitutes a cytoplasmic determinant that is segregated to germ cells where it plays an essential role in the establishment and preservation of the germ line. A monoclonal antibody was isolated in 1982 that binds germ plasm in C. elegans, however, the antigens recognized by this antibody were not identified. We found that this antibody recognizes a shared epitope on at least four different proteins. Isolation and characterization of cDNAs encoding these proteins revealed that one was highly conserved in plants and animals. Loss of expression of this gene is associated with differentiation and loss of function mutations in this gene can result in precocious differentiation.