CENTROSOMES WITH STRIATED ROOTLETS IN RABBIT ZYGOTES

An electron microscopic study of the rabbit zygote has shown the prese nce of numerous paracrystalline structures (PSs) around the pronuclei. The majority of these structures are situated in the narrow space bet ween pronuclei. The PSs during interphase are associated with small de nse knobs, and filamentous material; some of them, namely those situat ed in the internuclear space, are also associated with striated rootle ts. The PS and its appendages form a complex which nucleates microtubu les during interphase and phase M. The structure of these complexes ch anges with the cell cycle. Striated rootlets disappear at G(2)/M. Dens e knobs and filamentous material separate from the PS, become loose an d associate with numerous microtubules at the poles of the first mitot ic spindle. PSs and their associated :structures are considered to be a newly discovered morphological form of the centrosome.