Abstract
Dental enamel development occurs in stages. The ameloblast cell layer is adjacent to, and is responsible for, enamel formation. When rodent pre-ameloblasts become tall columnar secretory-stage ameloblasts, they secrete enamel matrix proteins, and the ameloblasts start moving in rows that slide by one another. This movement is necessary to form the characteristic decussating enamel prism pattern. Thus, a dynamic system of intercellular interactions is required for proper enamel development. Cadherins are components of the adherens junction (AJ), and they span the cell membrane to mediate attachment to adjacent cells. p120 stabilizes cadherins by preventing their internalization and degradation. So, we asked if p120-mediated cadherin stability is important for dental enamel formation. Targeted p120 ablation in the mouse enamel organ had a striking effect. Secretory stage ameloblasts detached from surrounding tissues, lost polarity, flattened, and ameloblast E- and N-cadherin expression became undetectable by immunostaining. The enamel itself was poorly mineralized and appeared to be composed of a thin layer of merged spheres that abraded from the tooth. Significantly, p120 mosaic mouse teeth were capable of forming normal enamel demonstrating that the enamel defects were not a secondary effect of p120 ablation. Surprisingly, blood-filled sinusoids developed in random locations around the developing teeth. This has not been observed in other p120-ablated tissues and may be due to altered p120-mediated cell signaling. These data reveal a critical role for p120 in tooth and dental enamel development and are consistent with p120 directing the attachment and detachment of the secretory stage ameloblasts as they move in rows.
Highlights
Dental enamel development progresses through defined stages that can be observed by the changing morphology of the enamel organ that covers the developing murine tooth
To confirm that cadherins are expressed in tissues responsible for the developing mouse first molar, Quantitative Real-time PCR (qPCR) analysis was performed on first molar enamel organs (EO) at two specific stages of development
The results demonstrated that E, and N-cadherins are each expressed during the secretory (P5-7) and maturation stage (P9-11) of enamel development (Fig. 1)
Summary
Dental enamel development progresses through defined stages that can be observed by the changing morphology of the enamel organ that covers the developing murine tooth. The ameloblasts of the enamel organ are a single layer of tall, columnar cells that are responsible for enamel development at their apical cell surface and attach to the stratum intermedium of the enamel organ at their basal end. During the secretory stage of enamel development, enamel matrix proteins are secreted and long thin crystallites form normal to the secretory surface of the ameloblasts. These crystallites will eventually span the distance between the dentin and the enamel surface. Rows of ameloblasts will move past each other to form the decussating enamel rod pattern that is characteristic of rodent dental enamel [3,4,5]
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