An autoradiographic investigation of tooth renewal in the purple sea urchin (Strongylocentrotus purpuratus)

The DNA‐synthesizing cells in the tooth of the purple sea urchin were labeled with tritiated thymidine and detected with autoradiography. After one hour many cells were labeled in the abaxial peripheral layer of the soft, aboral end of the tooth. These cells were the chief source of new cells for tooth renewal. With time, the cells labeled in the abaxial peripheral layer (and several generations of their progeny) migrated as a zone of labeled cells. The zone migrated in an oral direction toward the hard, biting end of the tooth. The labeled cells in the leading part of the migrating zone occupied lateral positions in the tooth, and the labeled cells in the trailing part of the migrating zone occupied a median position. The time of tooth renewal in young adult specimens of the purple sea urchin maintained in the laboratory is approximately 75 days.