Heavy bodies detected by NOR-silver staining in sea urchin embryos: In centrifuged eggs and in late anaphase blastomeres

Particles which were stained by NOR-silver staining were detected in the cytoplasm of the sea urchin eggs (Amikura and Ihnuma, 1984). During early development, the cyclic appearance of these cytoplasmic particles (CPs) was observed; they were present between interphase and prophase, and were absent between metaphase and anaphase. The CPs reappeared at telophase when chromosomal vesicles were formed and remained in interphase (Amikura et al, 1989). Electron microscopic study of centrifuged sea urchin eggs showed that these CPs were identical to the heavy bodies (Afzelius, 1957), which were supposed to be nuclear origin. In addition, the CPs began to appear near the chromosomal vesicles as early as at late anaphase.