DEVELOPMENTAL EXPRESSION PATTERNS OF BCL-2, BCL-X, BAX, AND BAK IN TEETH

The ontogenic profile of expression of four members of the Bcl-2 famil y (Bcl-2, Bcl-x, Bar and Bak) was examined in the mouse by immunohisto chemistry using paraffin sections. All four members were expressed in changing patterns during critical stages of tooth morphogenesis. Expre ssion was detected in epithelial cell populations including the dental lamina, internal dental epithelium (IDE; differentiating ameloblasts) , stratum intermedium and stellate reticulum cells, as well as in the condensed dental mesenchyme. The temporospatial localization of the va rious members of the Bcl-2 family in dental epithelium and mesenchyme showed striking overlapping areas but often their expression patterns differed. In general, contemporaneous co-expression of the Bcl-2 and B ar proteins, and of the Bcl-x and Bak proteins was noted in various ty pes of cells during the developmental process, with the intensity of B cl-2 > Bax and of Bak > Bcl-x. Expression was pronounced at sites wher e interaction between surface ectoderm and induced mesenchyme takes pl ace, and at the enamel knot, which is regarded as organization/regulat ing center for tooth development. Around birth, after the structural m aturation was accomplished, the expression was down-regulated. The abs ence of elevated expression of each of these four members of the Bcl-2 family after birth in the teeth suggests that these proteins are rele vant during the accomplishment of the basic architecture but not once the structure of the tooth is established.