PCNA and ameloblastoma: Similar to that observed in both the ameloblastoma and DLRs, the intermediate cells (or middle dental epithelium, equivalent to the central cells in Ame/DLRs) of the shark successional lamina show a similar pattern of Bmi1, PH3 and PCNA expression (Fig. 2), which indicates that this is a dynamic and highly proliferative region of the lamina, capable of maintaining stem cells necessary for continued tooth production.