An immunohistochemical study of the expression of heat-shock protein-25 and cell proliferation in the dental pulp and enamel organ during odontogenesis in rat molars.
OBJECTIVE
The aim of this study is to clarify the functional significance of heat-shock protein (HSP)-25 during tooth development.


METHODS
We compared the expression of HSP-25 in the dental epithelial and mesenchymal cells with their proliferative activity during odontogenesis in rat molars on postnatal days 1-100 by immunohistochemistry using anti-HSP-25 and anti-5-bromo-2'-deoxyuridine (BrdU) for cell proliferation assay.


RESULTS
On day 1, BrdU-immunoreactive cells were densely located in the inner enamel epithelium in the cervical loop and intercusped areas and the dental pulp adjacent to them, whereas HSP-25-immunoractivity (IR) was restricted to the cusped area where odontoblasts and ameloblasts had already differentiated. Subsequently, BrdU-IR shifted in the apical direction to be localized around Hertwig's epithelial root sheath during days 5-30, never overlapping with concomitantly apically-shifted HSP-25-IR. On days 60-100, BrdU-immunoreactive cells were hardly recognizable in the dental pulp, where HSP-25-IR was exclusively localized in the odontoblast layer. Furthermore, the odontoblast- and ameloblast-lineage cells exhibited two steps in the expression of HSP-25 throughout the postnatal stages: first, dental epithelial and pulpal mesenchymal cells showed a weak IR for HSP-25 after the cessation of their proliferative activity, and subsequently odontoblasts and ameloblasts consistently expressed an intense HSP-25-IR.


CONCLUSIONS
Odontoblast- and ameloblast-lineage cells acquire HSP-25-IR after they complete their cell division, suggesting that this protein acts as a switch between cell proliferation and differentiation during tooth development. The consistent expression of HSP-25-IR in the formative cells may be involved in the maintenance of their functional integrity.
Nakasone
Naohiro
N
Division of Anatomy and Cell Biology of the Hard Tissue, Department of Tissue Regeneration and Reconstruction, Niigata University Graduate School of Medical and Dental Sciences, 2-5274 Gakkocho-dori, Niigata 951-8514, Japan.
Yoshie
Hiromasa
H
Ohshima
Hayato
H
D000566:Amelogenesis / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn; D001973:Bromodeoxyuridine / Q000032:analysis; D049109:Cell Proliferation; D003782:Dental Pulp / Q000737:chemistry / Q000254:growth & development*; D003810:Dentinogenesis / Q000502:physiology; D004658:Enamel Organ / Q000737:chemistry / Q000254:growth & development*; D055551:HSP27 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000032:analysis*; D007150:Immunohistochemistry / Q000379:methods; D008963:Molar / Q000737:chemistry / Q000254:growth & development*; D009363:Neoplasm Proteins / Q000032:analysis*; D009805:Odontogenesis / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D055551:HSP27 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C486114:Hspb1 protein, rat; D009363:Neoplasm Proteins; D001973:Bromodeoxyuridine