Evidence for polar cytoplasm nuage in rat oocytes

In many organisms oocytes contain dark-staining material, termed nuage, tha t is concentrated at one pole of the oocyte cytoplasm and that influences t he further development of the oocyte after fertilization. In mammalian oocy tes, ultrastructural studies have detected small patches of nuage-like mate rial, but thus far no nuage-rich zone of polar cytoplasm has been reported. Here, we report that when large sections of rat ovary embedded in methacry late resin are stained with toluidine blue and surveyed, many oocytes conta in a narrow, sharply defined, basophilic zone of polar cytoplasm that appea rs analogous to the polar cytoplasm of Xenopus and other non-mammalian spec ies. This basophilic polar cytoplasm was common in multilaminar follicles a nd was not visible in smaller, primordial follicles. In one out of five ooc ytes stimulated with hCG to complete the first meiotic division, a relative ly faint region of cortical basophilia was detectable. Further studies will be needed to ascertain if this nuage-like material has an influence upon t he development of oocytes similar to that seen in non-mammalian species.