The immunohistochemical localization of Bax and Bcl-2 and their relation to apoptosis during amelogenesis in developing rat molars

Bax and Bcl-2 are members of a family of intracellular, membrane-associated proteins that regulate programmed cell death. It has been suggested that, when Bax predominates, programmed cell death is accelerated and the apoptos is inhibitory activity of Bcl-2 is suppressed. The present study was undert aken to immunohistochemically (IHC) localize Bax and Bcl-2 in the cells of the enamel organ during amelogenesis in rat molars. Also, apoptotic cells w ere detected by TUNEL staining. The IHC intense localization of Bcl-2 and l ight staining for Bax in the pre-ameloblasts suggest that apoptosis is inhi bited in the proliferating pre-ameloblasts. This is consistent with an abse nce of TUNEL staining for apoptosis in these cells. However, in the late se cretory and transition ameloblasts, and adjacent stratum intermedium, evide nce of apoptosis of the ameloblasts was observed. Bax and Bcl-2 were co-loc alized in the proximal ends of late secretory, transition and early maturat ion-stage ameloblasts, but immunoreactivity for Bax markedly increased in t he proximal ends of late secretory and transition ameloblasts, while the Bc l-2 staining appeared to be lighter. This suggests that Bax antagonized Bcl -2 function, limiting the ability of Bcl-2 to prolong cell survival. In the early maturation stage, Bax staining faded while the immunoreactivity for Bcl-2 increased. Evidence of distinct apoptosis was reduced in the early ma turation stage ameloblasts. When related to the occurrence of apoptosis dur ing amelogenesis, the relative intensity of expression of Bax and Bcl-2 cha nged in a pattern consistent with that observed in other cell lines. This i ndicates that these proteins play essential roles in the process of ameloge nesis, as predicted by their proposed mechanisms of action in the control o f apoptosis. (C) 2001 Elsevier Science Ltd. All rights reserved.