title: Hertwig's Epithelial Root Sheath Fate during Initial Cellular Cementogenesis in Rat Molars.
abstract: To elucidate the fate of the epithelial root sheath during initial cellular cementogenesis, we examined developing maxillary first molars of rats by immunohistochemistry for keratin, vimentin, and tissue non-specific alkaline phosphatase (TNALP) and by TdT-mediated dUTP nick end labeling (TUNEL). The advancing root end was divided into three sections, which follow three distinct stages of initial cellular cementogenesis: section 1, where the epithelial sheath is intact; section 2, where the epithelial sheath becomes fragmented; and section 3, where initial cellular cementogenesis begins. After fragmentation of the epithelial sheath, many keratin-positive epithelial sheath cells were embedded in the rapidly growing cellular cementum. A few unembedded epithelial cells located on the cementum surface. Dental follicle cells, precementoblasts, and cementoblasts showed immunoreactivity for vimentin and TNALP. In all three sections, there were virtually no cells possessing double immunoreactivity for vimentin-keratin or TNALP-keratin and only embedded epithelial cells showed TUNEL reactivity. Taken together, these findings suggest that: (1) epithelial sheath cells divide into two groups; one group is embedded in the cementum and thereafter dies by apoptosis, and the other survives on the cementum surface as epithelial cell rests of Malassez; and (2) epithelial sheath cells do not undergo epithelial-mesenchymal transition during initial cellular cementogenesis.
authors.affiliation: Department of Developmental Biology of Hard Tissue, Hokkaido University Graduate School of Dental Medicine , Sapporo, Japan.
authors.forename: Tsuneyuki
authors.initials: T
authors.lastname: Yamamoto
authors.affiliation: Department of Developmental Biology of Hard Tissue, Hokkaido University Graduate School of Dental Medicine , Sapporo, Japan.
authors.forename: Tamaki
authors.initials: T
authors.lastname: Yamada
authors.affiliation: Department of Developmental Biology of Hard Tissue, Hokkaido University Graduate School of Dental Medicine , Sapporo, Japan.
authors.forename: Tomomaya
authors.initials: T
authors.lastname: Yamamoto
authors.affiliation: Department of Developmental Biology of Hard Tissue, Hokkaido University Graduate School of Dental Medicine , Sapporo, Japan.
authors.forename: Tomoka
authors.initials: T
authors.lastname: Hasegawa
authors.affiliation: Department of Developmental Biology of Hard Tissue, Hokkaido University Graduate School of Dental Medicine , Sapporo, Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Hongo
authors.affiliation: Division of Biochemistry, Niigata University Graduate School of Medical and Dental Sciences , Niigata, Japan.
authors.forename: Kimimitsu
authors.initials: K
authors.lastname: Oda
authors.affiliation: Department of Developmental Biology of Hard Tissue, Hokkaido University Graduate School of Dental Medicine , Sapporo, Japan.
authors.forename: Norio
authors.initials: N
authors.lastname: Amizuka
keywords: Hertwig’s epithelial root sheath; cellular cementum; cementoblasts; epithelial-mesenchymal transition; rat molars