Formation of Tight and Gap Junctions in the Inner Enamel Epithelium and Preameloblasts in Human Fetal Tooth Germs

Abstract

Human fetal primary tooth germs in the cap stage were fixed with a glutaraldehyde-formaldehyde mixture, and formative processes of tight and gap junctions of the inner enamel epithelium and preameloblasts were examined by means of freeze-fracture replication. Chains of small clusters of particles on the plasma membrane P-face of the inner enamel epithelium and preameloblasts were the initial sign of tight junction formation. After arranging themselves in discontinuous, linear arrays in association with preexisting or forming gap junctions, these particles later began revealing smooth, continuous tight junctional strands on the plasma membrane P-face and corresponding shallow grooves of a similar pattern on the E-face. Although they exhibited evident meshwork structures of various extents at both the proximal and distal ends of cell bodies, they formed no zonulae occludentes. Small assemblies of particles resembling gap junctions were noted at points of cross linkage of tight junctional strands; but large, mature gap junctions no longer continued into the tight junction meshwork structure. Gap junctions first appeared as very small particle clusters on the plasma membrane P-face of the inner enamel epithelium. Later two types of gap junctions were recognized: one consisted of quite densely aggregated particles with occasional particle-free areas, and the other consisted of relatively loosely aggregated particles with particle-free areas and aisles. Gap junction maturation seemed to consist in an increase of particle numbers. Fusion of gap junctions in the forming stage too was recognized. The results of this investigation suggest that, from an early stage in their development, human fetal ameloblasts possess highly differentiated cell-to-cell interrelations.

Expression of connexin 43 and ZO-1 in differentiating ameloblasts and odontoblasts from rat molar tooth germs

“…Expression of Cx43 between ameloblasts is consistent with the previous reports that showed gap junctions at all stages of amelogenesis (Sasaki et al 1981(Sasaki et al , 1985. Since these junctions are involved in cell-cell communication, they may play an important role during the coordinated events that lead to the full differentiation of ameloblasts.…”

Immunohistochemical localization of connexin 43 in the developing tooth germ of rat

“…The ordered arrangement of matrix in enamel and dentine suggests that both types of cell exhibit a high degree of organization and cell communication. Gap junctions have been demonstrated between the cells in the developing tooth germ by transmission electron microscopy (Garant 1972;Kallenbach 1977;Warshawsky 1978;Weinstock 1981;Sasaki et al 1985;Sasaki and Garant 1986), but it is difficult to determine their incidence from thin sections or freeze-etching replicas. Further, the members of the connexin family that constitute gap junctions in the developing tooth germ are yet to be determined.…”