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Immunohistochemical Localization of -Smooth Muscle Actin During Rat Molar Tooth Development

Akihiro Hosoya, Hiroaki Nakamura, Tadashi Ninomiya, Kunihiko Yoshiba, Nagako Yoshiba, Hiroyuki Nakaya, Shigeyuki Wakitani, Hirohito Yamada, Etsuo Kasahara and Hidehiro Ozawa

Department of Oral Histology (AH,HNakamura), Institute for Dental Science (TN,HO), and Department of Endodontics and Operative Dentistry (HY,EK), Matsumoto Dental University, Shiojiri, Nagano, Japan; Division of Cariology, Department of Oral Health Science, Course for Oral Life Science, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan (KY,NY); and Department of Orthopedic Surgery, Shinshu University Graduate School of Medicine, Matsumoto, Nagano, Japan (HNakaya,SW)

Correspondence to: Akihiro Hosoya, DDS, PhD, Department of Oral Histology, Matsumoto Dental University, 1780 Gobara Hirooka, Shiojiri, Nagano 399-0781, Japan. E-mail: hosoya{at}po.mdu.ac.jp

The dental follicle contains mesenchymal cells that differentiate into osteoblasts, cementoblasts, and fibroblasts. However, the characteristics of these mesenchymal cells are still unknown. -Smooth muscle actin (-SMA) is known to localize in stem cells and precursor cells of various tissues. In the present study, to characterize the undifferentiated cells in the dental follicle, immunohistochemical localization of -SMA was examined during rat molar tooth development. Rat mandibles were collected at embryonic days (E) 15–20 and postnatal days (P) 7–28. Immunohistochemical stainings for -SMA, periostin, Runt-related transcription factor-2 (Runx2), tissue nonspecific alkaline phosphatase (TNAP), and bone sialoprotein (BSP) were carried out using paraffin-embedded sections. -SMA localization was hardly detected in the bud and cap stages. At the early bell stage, -SMA-positive cells were visible in the dental follicle around the cervical loop. At the late bell to early root formation stage (P14), these cells were detected throughout the dental follicle, but they were confined to the apical root area at P28. Double immunostaining for -SMA and periostin demonstrated that -SMA-positive cells localized to the outer side of periostin-positive area. Runx2-positive cells were visible in the -SMA-positive region. TNAP-positive cells in the dental follicle localized nearer to alveolar bone than Runx2-positive cells. BSP was detected in osteoblasts as well as in alveolar bone matrix. These results demonstrate that -SMA-positive cells localize on the alveolar bone side of the dental follicle and may play a role in alveolar bone formation. (J Histochem Cytochem 54:1371–1378, 2006)

Key Words: -smooth muscle actin • dental follicle • undifferentiated cell • rat molar • periostin

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