Gene Expression and Localization of Insulin-like Growth Factors and Their Receptors throughout Amelogenesis in Rat Incisors

Abstract

(SO) S U M M A R Y Insulin-like growth factors (IGFs) are expressed in many tissues and control cell differentiation, proliferation, and apoptosis. In teeth, the temporo-spatial pattern of expression IGFs and their receptors has not been fully characterized. The purpose of this study was to obtain a comprehensive profile of their expression throughout the life cycle of ameloblasts, using the continuously erupting rat incisor model. Upper incisors of young male rats were fixed by perfusion, decalcified, and embedded in paraffin. Sections were processed for in situ hybridization and immunohistochemistry. mRNA and protein expression profiles IGF-I, IGF-II, IGF-IR, and IGF-IIR mRNA were essentially identical. At the apical loop of the incisor, very strong signals were seen in the outer enamel epithelium while the inner enamel epithelium showed a moderate reaction. In the region of ameloblasts facing pulp, inner enamel epithelium cells were still moderately reactive while signals over the outer enamel epithelium were slightly reduced. In the region of ameloblasts facing dentin and the initial portion of the secretory zone, signals in ameloblasts were weak while those over the outer enamel epithelium were strong. In the region of postsecretory transition, signals in both ameloblasts and papillary layer cells gradually increased. In maturation proper, signals in ameloblasts appeared as alternating bands of strong and weak reactivities, which corresponded to the regions of ruffle-ended and smooth-ended ameloblasts, respectively. Papillary layer cells also showed alternations in signal intensity that matched those in ameloblasts. These results suggest that the IGF family may act as an autocrine/paracrine system that influences not only cell differentiation but also the physiological activity of ameloblasts. (J Histochem Cytochem 54:243-252, 2006)

Rabson-Mendenhall syndrome: two case reports and a brief review of the literature

“…This case is of special interest because it is the fi rst reported case of leprechaunism with these features, because most patients do not survive long enough to develop them. Yamamoto et al 22 found mRNA and protein signals for IGF-I and -II and their receptors in enamel organ of rat incisors throughout amelogenesis. Hence, there is a strong possibility that these molecules act as an autocrine/paracrine system that infl uences not only cell differentiation but also the physiological activity of ameloblasts.…”

MAPK mediates Hsp25 signaling in incisor development

“…The expression pattern is similar to the localization of BMP4, FGF3, FGF9, and FGF10 in the developing incisor (Harada et al 1999(Harada et al , 2002Wang et al 2007). IGF and EGF also aVect ameloblast diVerentiation, and are localized in the incisor enamel formation region (Joseph et al 1999;Martineau-Doizé et al 1991;Yamamoto et al 2006). Hsp25 is expressed in both ameloblasts and odontoblasts.…”

Induction of enamel matrix protein expression in an ameloblast cell line co-cultured with a mesenchymal cell line in vitro

“…Among these factors, the insulin-like growth factors (IGFs) have been proposed as autocrine/paracrine regulators of in vivo tooth development (Caton et al 2005;Yamamoto et al 2006) and the molecular weight of IGF is less than 12.5 kDa. Therefore, IGFs are promising candidate soluble factors for mediation of the stimulation of ameloblastin mRNA and protein expression in HAT-7 cells.…”