Fine structure of rat incisor ameloblasts in transition between enamel secretion and maturation stages

Kallenbach, Ernst

doi:10.1016/0040-8166(74)90030-5

Cited by 48 publications

(51 citation statements)

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“…The large, irregular bodies with "lipid-like" membranes appear to correspond to the electron dense phagosomes of the ameloblast (Kallenbach, 1974). The close association between the beccublast and the secreted tissue is also seen in the secretory phase of the rat ameloblast (Kallenbach, 1974).…”

Section: Discussionmentioning

confidence: 82%

“…Allan (1967) and Reith and Butcher (1967) suggested that the ameloblasts go through a transitional stage in which they change from protein synthesising and secreting cells to ones active in absorptive and transport processes. Kallenbach (1974) showed that fine structural differences occurred in the rat incisor ameloblasts related to the two types activity of these cells.…”

Section: Introductionmentioning

confidence: 99%

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The cells that secrete the beaks in octopods and squids (Mollusca, Cephalopoda)

Dilly

Nixon

1976

Cell Tissue Res.

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Summary. A single layer of cells secretes the hard cephalopod beaks. The beccublasts are tall columnar cells that separate the beak from the surrounding buccal muscles, and must serve to attach these muscles to the beak. Within the cell layer there are three types of cells. The first, and most frequently found contain cell-long fibrils. These fibrils may have contractile and tensile properties. Complex trabeculae extend from the beccublasts into the matrix of the beak. The fibrils are attached to these trabeculae and at the other end of the cells they are anchored near to the beccublast-muscle cell interface, closely associated with the muscles that move the beak.The second group of cells contain masses of endoplasmic reticulum the cysternae of which are arranged along the long axis of the cell. These cells also contain dense granules and are probably the major source of beak hard tissue. It is probable that each cell secretes its own column of beak hard tissue. The third group of cells contains a mixture of fibrils and secretory tissue.In the beccublast layer there are changes in the proportion of the three types of cells depending upon the region sampled. In the region where growth is most active there are mostly secretory cells, whereas near the biting and wearing tip there are mainly anchoring type cells.

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Section: Discussionmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

The cells that secrete the beaks in octopods and squids (Mollusca, Cephalopoda)

Dilly

Nixon

1976

Cell Tissue Res.

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“…By the end of the secretory stage the enamel crystals are full-length and the enamel layer as a whole is as thick as it will ever be, but it has only about 14% of the mineral as it will have when the tooth erupts (15). Following the secretory stage there is then a transition during which the ameloblasts greatly reduce their secretion of enamel proteins (16) and convert to maturation ameloblasts (17). During the maturation stage, mineral is deposited exclusively on the sides of pre-existing enamel crystallites (18), which grow in width and thickness until further growth is prevented by contact with adjacent crystals (19,20).…”

mentioning

confidence: 99%

Hypomaturation Enamel Defects in Klk4 Knockout/LacZ Knockin Mice

Simmer

Lertlam

et al. 2009

Journal of Biological Chemistry

133

184

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Kallikrein 4 (Klk4) is believed to play an essential role in enamel biomineralization, because defects in KLK4 cause hypomaturation amelogenesis imperfecta. We used gene targeting to generate a knockin mouse that replaces the Klk4 gene sequence, starting at the translation initiation site, with a lacZ reporter gene. Correct targeting of the transgene was confirmed by Southern blot and PCR analyses. Histochemical X-gal (5-bromo-4-chloro-3-indolyl-␤-D-galactopyranoside) staining demonstrated expression of ␤-galactosidase in maturation stage ameloblasts. No X-gal staining was observed in secretory stage ameloblasts or in odontoblasts. Retained enamel proteins were observed in the maturation stage enamel of the Klk4 null mouse, but not in the Klk4 heterozygous or wild-type mice. The enamel layer in the Klk4 null mouse was normal in thickness and contained decussating enamel rods but was rapidly abraded following weaning, despite the mice being maintained on soft chow. In function the enamel readily fractured within the initial rod and interrod enamel above the parallel enamel covering the dentinoenamel junction. Despite the lack of Klk4 and the retention of enamel proteins, significant levels of crystal maturation occurred (although delayed), and the enamel achieved a mineral density in some places greater than that detected in bone and dentin. An important finding was that individual enamel crystallites of erupted teeth failed to grow together, interlock, and function as a unit. Instead, individual crystallites seemed to spill out of the enamel when fractured. These results demonstrate that Klk4 is essential for the removal of enamel proteins and the proper maturation of enamel crystals.Dental enamel is composed of highly ordered, very long crystals of calcium hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ). Mature enamel crystallites are about 70 nm wide and 30 nm thick, but are of unmeasurable length (1), probably extending all the way from the dentin layer to the surface of the tooth (2). Enamel crystallites are organized into bundles called rods, with about 10,000 parallel crystals in a rod (3). Each enamel rod is the product of a single ameloblast, the cell type that forms a continuous sheet over the developing enamel and orchestrates its formation. Dental enamel of erupted teeth is ϳ95% mineral (by weight) (4), with most of the non-mineral component being water. Protein comprises Ͻ1% of its weight. Forming enamel, however, is over 30% protein (5). Much of the protein is reabsorbed by ameloblasts and degraded in lysosomes (6, 7), but extracellular proteases also play a role in matrix protein removal (8 -10).Dental enamel formation is divided into secretory, transition, and maturation stages (11,12). During the secretory stage, enamel crystals grow primarily in length. As the crystals extend, the enamel layer expands. Enamel crystallites lengthen along a mineralization front at the secretory surface of the ameloblast cell membrane. There, mineral deposits rapidly on the crystallite tips, and very slowly on their sides...

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“…7). The gap between the distal cell membrane and the enamel [6] could not be confirmed. Some large and small vesicles and tubular structures were recognized in the distal cytoplasm, but their structures and distributions were varied (Fig.…”

Section: Methodsmentioning

confidence: 92%

“…However, no study has yet been carried out on the electron microscopic ultrastructure of this particular maturation stage. KALLEN-BACH [6] has shown that the maturation stage begins when the ameloblast becomes shortened after the transitional stage, but his study was not related to modulation. Accordingly, the present authors carried out serial electron microscopic observations of the region in the rat upper incisor where SA can be seen directly after the transitional stage, using undecalcified sections.…”

Section: Introductionmentioning

confidence: 99%