GERM PLASM IN CAENORHABDITIS-ELEGANS, DROSOPHILA AND XENOPUS

Special cytoplasm, called germ plasm, that is essential for the differ entiation of germ cells is localized in a particular region of Caenorh abditis elegans, Drosophila and Xenopus eggs. The mode of founder cell formation of germline, the origin and behavior of the germline granul es, and the molecules localized in germline cells are compared in thes e organisms. The common characteristics of the organisms are mainly as follows. First, the founder cells of germline are established before the initiation of gastrulation. Second, the germline granules or their derivatives are always present in germline cells or germ cells throug hout the life cycle in embryos, larvae, and adults. Lastly, among the proteins localized in the germ plasm, only Vasa protein or its homolog is detected in the germline cells or germ cells throughout the life c ycle. As the protein of vasa homolog has been reported to be also loca lized in the germline-specific structure or nuage in some of the organ isms without the germ plasm, the possibility that the mechanism for di fferentiation of primordial germ cells is basically common in all orga nisms with or without the germ plasm is discussed.