Immunodetection of Enamel- and Cementum-Related (Bone) Proteins at the Enamel-Free Area and Cervical Portion of the Tooth in Rat Molars

Abstract

Enamel and dentin at the cervical portion of the tooth are frequently covered by a collagen-free matrix referred to as acellular afibrillar cementum (AAC). It is believed that AAC deposition occurs when the enamel organ is displaced or disrupted, and mesenchymal cells from the dental follicle gain access to the tooth surface, differentiate into cementoblasts, and secrete noncollagenous proteins typically found in collagen-based mineralized tissues. A similar thin layer of mineralized matrix is found at the enamel-free area (EFA) of rodent molars, but in this case the matrix is covered by inner enamel epithelium (IEE) throughout development. We have, therefore, used this site as a paradigm to test the hypothesis that typical mesenchymal matrix proteins can also be found in association with epithelial cells. To this end, we have analyzed the presence and distribution of enamel-and cementum-related matrix proteins at the EFA and at the cervical portion of the tooth. Rat mandibular molars were processed for colloidal gold immunolabeling with antibodies to amelogenins, bone sialoprotein (BSP), osteopontin (OPN), osteocalcin (OC), and dentin sialoprotein (DSP), and the plasma proteins ␣ 2 HS-glycoprotein and albumin. The EFA matrix was immunoreactive for amelogenins as well as for BSP, OPN, OC, and ␣ 2 HS-glycoprotein, but not for albumin and DSP. The AAC was, similar to the EFA matrix, labeled for BSP, OPN, OC, and ␣ 2 HSglycoprotein. These data show for the first time that the EFA matrix is comprised of a mixture of enamel-and cementum-related proteins, a situation that parallels the distribution of matrix constituents at the cervical portion of the tooth. Since the EFA matrix is deposited on top of the mineralized dentin, and since the enamel organ seals off the forming matrix, it is concluded that EFA cells are responsible for the production of these proteins. Consistent with previous reports showing that epithelial cells can produce both BSP and OPN in some circumstances, the data also suggest that AAC may be deposited by cells of epithelial origin. Furthermore, they lend support to the possibility that cells derived from Hertwig's epithelial root sheath may likewise be capable of producing cementum matrix proteins. (J Bone Miner Res 1997;12:367-379)

Immunocytochemical Study of Amelogenin Deposition during the Early Odontogenesis of Molars in Alendronate-treated Newborn Rats

“…Even though it has been reported that odontoblasts express amelogenin mRNA (Veis et al 2000;Oida et al 2002) and that amelogenin is expressed in relatively small amounts in a temporal-dependent pattern by rodent odontoblasts (Papagerakis et al 2003), the odontoblasts were never labeled in either the control or treated specimens, thus confirming previous studies with the same antibody (Nanci et al 1996;Bosshardt and Nanci 1997;Arana-Chavez and Nanci 2001). At least 14 isoforms are translated by an alternative splicing that takes place during amelogenin processing (Tompkins et al 2005b).…”

Epithelial Dlx-2 Homeogene Expression and Cementogenesis

“…This was also shown by the presence in root-lining cells of several epithelial markers, such as E-cadherin (Terling et al 1998), and an enamel protein, the amelin/ameloblastin/sheathlin studied at the mRNA level (Fong et al 1996) and protein level (this study). Ameloblastin was used and clearly evidenced in this study rather than the main enamel protein amelogenin, which appeared to be detected lining the root surface only by electron microscopy (Bosshardt and Nanci 1997). This observed patchwork/lattice of Dlx-2 positive cells along the root surface may correspond to the different origins of cementoblasts: one group would derive from root epithelium and the other from the ectomesenchyme of the follicular sac (Cho and Garant 1988;Bosshardt and Schroeder 1996).…”

Mineralization process during acellular cementogenesis in rat molars: a histochemical and immunohistochemical study using fresh-frozen sections

“…the epithelial sheath cells transform into cementoblasts to generate the initial cementum (Thomas 1995;Bosshardt and Nanci 1997;Bosshardt et al 1998;Zeichner-David et al 2003;Bosshardt 2005). The following points established in the study are: (1) Related to point (1) mentioned above, Kaneko et al (1999) have reported that the epithelial cells migrate into the periodontal ligament, or die immediately after the onset of root dentin formation in rat molars.…”