title: Cellular turnover in epithelial rests of Malassez in the periodontal ligament of the mouse molar.
abstract: Fragments of Hertwig's epithelial root sheath persist in the periodontal ligament (PDL) in small clusters known as epithelial rests of Malassez (ERM). It is generally agreed that ERM are maintained as a quiescent and exclusively dental epithelial cluster in PDL. However, we speculate that homeostasis and cellular turnover underlies cluster maintenance. We also hypothesize that the fate of ERM clusters - diminishing or remaining - might be regulated via the presence or absence of epithelial stem cells therein. Histological analysis of aging mouse molar PDL showed that ERM clusters gradually increase in size with increasing age. Immunocytochemistry and cell culture revealed that ERM clusters contained Ki67-positive cells and were able to expand when brought in culture. The TdT-mediated biotin-dUTP nick-end labeling (TUNEL) procedure also detected signs of apoptosis. Finally, we identified putative epithelial stem cells in the clusters by 5-bromo-2'-deoxyuridine (BrdU) pulse-chase experiments and immunohistochemistry, using the stem-cell marker leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5). The results suggest that ERM clusters are maintained in the PDL, via cellular turnover, throughout life.
authors.affiliation: Department of Anatomy, Nihon University School of Dentistry, Tokyo, Japan.
authors.forename: Kyoko
authors.initials: K
authors.lastname: Oka
authors.forename: Masakazu
authors.initials: M
authors.lastname: Morokuma
authors.forename: Kyoko
authors.initials: K
authors.lastname: Imanaka-Yoshida
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Sawa
authors.forename: Keitaro
authors.initials: K
authors.lastname: Isokawa
authors.forename: Masaki J
authors.initials: MJ
authors.lastname: Honda
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D001973:Bromodeoxyuridine / Q000378:metabolism; D018929:Cell Culture Techniques; D004847:Epithelial Cells / Q000166:cytology*; D005786:Gene Expression Regulation; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D019394:Ki-67 Antigen / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008963:Molar / Q000166:cytology* / Q000254:growth & development; D010513:Periodontal Ligament / Q000166:cytology*; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*; D013234:Stem Cells / Q000166:cytology* / Q000378:metabolism; D014092:Tooth Root / Q000166:cytology* / Q000254:growth & development
chemical_list: D019394:Ki-67 Antigen; C493597:Lgr5 protein, mouse; D043562:Receptors, G-Protein-Coupled; D001973:Bromodeoxyuridine