Differential Expression of the Tight Junction Proteins, Claudin‐1, Claudin‐4, Occludin, ZO‐1, and PAR3, in the Ameloblasts of Rat Upper Incisors

Abstract

Tight junctions (TJs) create a paracellular permeability barrier to restrict the passage of ions, small solutes, and water. Ameloblasts are enamel-forming cells that sequentially differentiate into preameloblasts, secretory, transition, and ruffle-ended and smooth-ended maturation ameloblasts (RAs and SAs). TJs are located at the proximal and distal ends of ameloblasts. TJs at the distal ends of secretory ameloblasts and RAs are welldeveloped zonula occludens, but other TJs are moderately developed but incomplete zonula occludens (ZO) or less-developed macula occludens. We herein examined the immunofluorescence localization of TJ proteins, 10 claudin isoforms, occludin, ZO-1, and PAR3, a cell polarity-related protein, in ameloblasts of rat upper incisors. ZO-1 and claudin-1 were detected at both ends of all ameloblasts except for the distal ends of SAs. Claudin-4 and occludin were detected at both ends of transition and maturation ameloblasts except for the distal ends of SAs. PAR3 was detected at the proximal TJs of all ameloblasts and faintly at the distal TJs of early RAs. These results indicate that functional zonula occludens formed at the distal ends of the secretory ameloblasts and RAs consisted of different TJ proteins. Therefore, the distal TJs of secretory ameloblasts and RAs may differentially regulate the paracellular permeability to create a microenvironment suitable for enamel deposition and enamel maturation, respectively. In addition, PAR3 may be principally involved in the formation and maintenance of the proximal, but not distal, TJs.

Importance of bicarbonate transport in pH control during amelogenesis — need for functional studies

“…These are a prerequisite for vectorial electrolyte secretion by restricting free transepithelial ion movements while permitting passage of certain ions between the cells (Hou, ; Melvin, Yule, Shuttleworth, & Begenisich, ; Steward, Ishiguro, & Case, ). The data are also in accordance with previous studies (Amasheh et al., ; Colegio, Van Itallie, McCrea, Rahner, & Anderson, ; Lal‐Nag & Morin, ) showing the expression of Cldn1, Cldn4, and Cldn8 in maturation‐stage ameloblasts (Hata, Kawamoto, Kawai, & Yamamoto, ; Inai, Sengoku, Hirose, Iida, & Shibata, ). As previous studies show, ion transporters necessary for intracellular and extracellular pH regulation such as Slc9a1/Nhe1, Slc4a2/Ae2, Slc4a4/Nbce1, Slc26a4/pendrin, and CFTR (Bronckers et al., ; Jalali et al., ; Lacruz et al., ) and the cytoplasmic Car2 isoform of carbonic anhydrases (Lacruz, Smith, Moffatt, et al., ; Reibring et al., ) are expressed by ameloblasts.…”

Modulation of Cell-Cell Junctional Complexes by Matrix Metalloproteinases

“…However, in incisors, pre-ameloblasts expressed ZO-1 at their basal end and little to no ZO-1 at their apical end. Once the ameloblasts reached the secretory stage, strong ZO-1 expression was observed at both the apical and basal ends (Unda et al, 2003;Inai et al, 2008). ZO-2, in contrast, was observed along lateral surfaces of pre-ameloblasts and across ameloblast cell membranes.…”

“…Claudin-1 (Joao and Arana-Chavez, 2004;Bello et al, 2007;Inai et al, 2008;Hata et al, 2010;Nishikawa and Abe, 2010), claudin-2 (Ohazama and Sharpe, 2007), claudin-4 (Inai et al, 2008), claudin-7 (Bello et al, 2007), and claudins -6, -8, -9, and -10 (Hata et al, 2010) were all shown to be expressed in ameloblasts. The most convincing data were generated from rat incisors and demonstrated that both claudin-1 (Nishikawa and Abe, 2010) and claudins-1 and -4 (Inai et al, 2008) were expressed in maturation-stage ameloblasts. Both studies showed that apical claudin-1 was removed from smooth-ended ameloblasts and was returned when the ameloblasts once again became ruffle-ended.…”

Dpysl4 Is Involved in Tooth Germ Morphogenesis through Growth Regulation, Polarization and Differentiation of Dental Epithelial Cells

“…3B). It has been demonstrated that polarized ameloblasts have specific characteristics including a columnar cell shape and the localization of molecules including Par3, ZO-1 and F-actin at the apical edge 12. Immunohistochemical analyses further showed that this localization of Par3, ZO-1 and F-actin was disrupted in the sh Dpysl4 molar epithelium as compared with control molars (Fig.…”

“…It has been reported that the formation of epithelial polarity is regulated by several signaling mechanisms including Phosphatidylinositol 3,4,5-trisphosphate (PIP 3 ) kinase, Glycogen synthase kinase 3 beta (GSK3β), Partitioning-defective protein (PAR) complex and the Ras homolog gene family (Rho) of proteins through the rearrangement of the actin cytoskeleton and microtubules 9. Functional ameloblasts also have specific characteristics, including a columnar cell shape and the localization of molecules such as Par3 , zonula occludens (ZO) and filamentous actin (F-actin) at their apical edge 12. These cells synthesize and secrete enamel-specific proteins from their apical ends through the transportation of secretory vesicles along microtubules 13, 14.…”