Insulin-like growth factor-I receptor in the cell biology of the ameloblast: an immunohistochemical study on the rat incisor.

The distribution of IGF-I receptor is reported in the odontogenic epithelium and mesenchyme of the continuously erupting mandibular incisor of the rat by immunohistochemistry using a polyclonal antibody specific to the IGF-I receptor. Odontogenic epithelium is a unique odontogenic sequence in that all stages of the complex life cycle of the ameloblast are represented along the length of the enamel-forming aspect of the tooth. Pre-ameloblasts become post-mitotic before secreting enamel matrix. When the full thickness of the enamel has been formed, a remarkable transition in phenotype takes place in the ameloblast. It changes from a protein secretory cell to one active in maturation of enamel matrix by removal of water and protein from the increasingly mineralized matrix. The distribution and intensity of IGF-I receptor expression varied with the phenotypic stages of the ameloblasts. Diffuse cellular staining for IGF-I receptor was found during the active secretory phase of amelogenesis. However, towards the end of this phase, the staining was confirmed to granular or vesicular structures within the cytoplasm. These granular deposits gradually decreased as the ameloblasts made the transition towards enamel maturation. This transition is accompanied by programmed cell death (apoptosis) of approximately 25% of the ameloblasts and cells in this zone did not stain for IGF-I receptor. With the onset of enamel maturation, diffuse staining of the ameloblast layer was re-established gradually and staining remained evident right up to the reduced enamel epithelium, which joins with the oral epithelium. Strong IGF-I receptor immunoreactivity was observed in the stratum basale and stratum spinosum of the adjacent labial gingival epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)