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M. Hormia(1*), C. Sahlberg(2), I. Thesleff(2), and T. Airenne(3)
Abstract. The attachment of the marginal gingiva to the tooth surface is mediated by a thin nonkeratinized epithelium termed the junctional epithelium (JE). Ultrastructural studies have revealed that the attachment of the JE to the tooth surface occurs through hemidesmosomes (HD) and a basal lamina-like extracellular matrix termed the internal basal lamina (IBL). We have previously shown that neither type IV collagen nor prototypic laminin, two common components of basement membranes (BM), is present in the IBL between the epithelium and the tooth. In the present study, we show that laminin-5 is a major component of the IBL in both rodent and human tissues. By using in situ hybridization, we also show that the cells of the JE express the LAMC2 gene of laminin-5. In other parts of gingival epithelium, LAMC2 gene expression is less prominent. Our results indicate that the epithelium-tooth interface is a unique structure wherein epithelial cells are induced to secrete a basal lamina containing laminin-5 and no other presently known laminin isoform.
Key words: basal lamina, epithelium, laminin-5, dentoepithelial junction.
Introduction
The junctional epithelium (JE) that links the gingiva to the tooth surface resembles phenotypically the basal cell layer of oral epithelium (Schroeder and Listgarten, 1977) but is unique in being attached both to a hard tooth surface and to a basement membrane (BM) facing the connective tissue. The structural features of the dento-epithelial junction have been well-characterized in earlier studies (Schroeder and Listgarten, 1977; Ten Cate, 1994). The cells of JE are attached both to the internal basal lamina (IBL, between epithelium and tooth) and to the external basal lamina (EBL, between epithelium and connective tissue) by means of hemidesmosomes (HD; Borradori and Sonnenberg, 1996; Green and Jones, 1996). However, in contrast to the EBL, the IBL often shows an incompletely delineated lamina densa and relatively indistinct anchoring filaments (Kobayashi et al., 1976; Schroeder and Listgarten, 1977; Sawada and Inoue, 1996).
Knowledge of the molecular composition and architecture of the dento-epithelial junction has thus far remained fragmentary. We have previously shown that alpha6-beta4 integrin, a HD-associated receptor glycoprotein (Carter et al., 1990; Stepp et al., 1990; Jones et al., 1991; Sonnenberg et al., 1991; Hynes, 1992), is polarized...