Immunohistochemical localization of heat shock protein 25 (HSP 25) during root formation of the rat molar

The present study investigated the immunohistochemical localization of heat shock protein 25 (HSP 25) of rat molar teeth during root formation. Most, probably all, cells of the epithelial rest of Malassez (ERM cells) had immunoreaction for laminin, a marker protein for basement membrane. During root formation, HSP 25 immunoreactivity was observed in odontoblasts, cells at the subodontoblastic layer, and those in close proximity to the acellular cementum. HSP 25-immunopositive cells at the subodontoblastic layer were present only at the apical region. Most HSP 25-immunoreactive cells in close proximity to the cementum lacked laminin immunoreactivity. However, at postnatal day 28 a small number of cells showed immunoreaction for both HSP 25 and laminin at the cervical and bifurcational regions. Under the electron microscope, most HSP 25-immunoreactive cells along the surface of the cementum were round and contained rich organelles such as mitochondria and rough endoplasmic reticulum. They lay between fiber bundles of the periodontal ligament. The localization and morphological features of these HSP 25-immunoreactive cells resemble those of cementoblasts. On the other hand, HSP 25-immunoreactive cells at the cervical region were oval and contained few cell organelles. They were closely apposed to each other, and separated from the surrounding tissues with basal lamina. These features were similar to those of mature ERM cells. In contrast, cells with microvillus-like processes and relatively rich mitochondoria, which were similar to immature ERM cells, had no immunoreaction for HSP 25. These results suggest that HSP 25 may be involved in shape alterations of ERM cells, cementoblasts, and odontoblasts during differentiation. Anat Rec 267:321–329, 2002. © 2002 Wiley-Liss, Inc.