Chikage Murakami

Enamelysin (Matrix Metalloproteinase-20): Localization in the Developing Tooth and Effects of pH and Calcium on Amelogenin Hydrolysis

The formation of dental enamel is a precisely regulated and dynamic developmental process. The forming enamel starts as a soft, protein-rich tissue and ends as a hard tissue that is is over 95% mineral by weight. Intact amelogenin and its proteolytic cleavage products are the most abundant proteins present within the developing enamel. Proteinases are also present within the enamel matrix and are thought to help regulate enamel development and to expedite the removal of proteins prior to enamel maturation. Recently, a novel matrix metalloproteinase named enamelysin was cloned from the porcine enamel organ. Enamelysin transcripts have previously been observed in the enamel organ and dental papillae of the developing tooth. Here, we show that the sources of the enamelysin transcripts are the ameloblasts of the enamel organ and the odontoblasts of the dental papilla. Furthermore, we show that enamelysin is present within the forming enamel and that it is transported in secretory vesicles prior to its secretion from the ameloblasts. We also characterize the ability of recombinant enamelysin (rMMP-20) to degrade amelogenin under conditions of various pHs and calcium ion concentrations. Enamelysin displayed the greatest activity at neutral pH (7.2) and high calcium ion concentration (10 mM). During the initial stages of enamel formation, the enamel matrix maintains a. neutral pH of between 7.0 and 7.4. Thus, enamelysin may play a role in enamel and dentin formation by cleaving proteins that are also present during these initial developmental stages.

Primary Structure of the Porcine 89-kDa Enamelin

The primary structure of the 89-kDa enamelin found in porcine secretory enamel at an early stage of development was investigated. The fragments of the enamelin cDNA were amplified by polymerase chain-reaction from the first-strand enamelin cDNA, and were sequenced. The results indicated that the 89-kDa enamelin consisted of 627 amino acid residues and had a molecular mass of 70,448. A hydrophobic domain is located in the region of the 21 st-62nd amino acid residues of the molecule. Acidic domains are located in two regions of the molecule-one in the region of the 135th-238th amino acid residues and the other in the C-terminal region. A basic domain is located in the region of the 239th-360th amino acid residues. The results also indicated that the low-molecular-weight enamelins were fragments derived from a prototype enamelin.

Localization of EMSP1 Expression During Tooth Formation and Cloning of Mouse cDNA

Enamel Matrix Serine Proteinase 1 (EMSP1) is a proteolytic enzyme that has been isolated from the developing enamel of pig teeth. Its apparent function is to degrade the organic matrix in preparation for enamel maturation. The expression of EMSP1 has never been investigated in another organism besides the pig, and EMSP1 expression in the enamel organ has never been specifically demonstrated in ameloblasts. Here we report the expression of recombinant pig EMSP1 (rpEMSP1), the generation of rabbit polyclonal antibodies against rpEMSPl, the characterization of the antibodies and EMSP1 expression by Western blot and immunohistochemical analyses, the cloning and characterization of a full-length cDNA encoding mouse EMSP1, and the localization of EMSP1 expression in ameloblasts in mouse day 14 first and second molars by in situ hybridization. The full-length mouse EMSP1 cDNA clone has 1237 nucleotides, excluding the poly(A+) tail, and encodes a preproprotein of 255 amino acids. Mouse EMSP1 shares 75% amino acid identity with pig EMSP1 and has three potential N-linked glycosylation sites, two of which are conserved in the pig homologue. Western blot analysis shows that the polyclonal antibodies are specific for EMSP1 and do not cross-react with trypsin. Immunohistochemistry of pig incisors shows discrete staining in the surface enamel at the earliest part of the maturation stage. In mouse molars, in situ hybridization gives a distinct and specific signal in maturation-stage ameloblasts, and in the junctional epithelium following tooth eruption. We conclude that EMSP1 is expressed by pig and mouse ameloblasts during the early maturation stage of amelogenesis.

Immunochemical and immunohistochemical study of the 27- and 29-kDa calcium-binding proteins and related proteins in the porcine tooth germ

Abstract Our previous report identified 27- and 29-kDa calcium-binding proteins in porcine immature dental enamel. In this study we revealed that the N-terminal amino acid sequences of the two proteins were identical: LLANPXGXIPNLARGPAGRSRGPPG. The sequence matches a portion of the amino acid sequence of the porcine sheath protein, sheathlin. Porcine tooth germs were investigated immunochemically and immunohistochemically using specific antibodies raised against synthetic peptide that included residues 13–25 of this sequence. The affinity-purified antibodies reacted with several proteins extracted from newly formed immature enamel in immunochemical analyses, especially protein bands migrating at 62, 35–45, 29, and 27 kDa in SDS-polyacrylamide gels. The largest protein detected was a weak band near 70 kDa. In immunochemical analyses of proteins extracted from the inner (old) immature enamel, the antibody reacted faintly with the 27- and 29-kDa proteins. In immunohistochemical preparations, the Golgi apparatus and secretory granules of the secretory ameloblast, and the surface layer of immature enamel showed immunoreactivity. The immunoreactivity of immature enamel just beneath the secretory face of the Tomes’ process was intense. No immunoreactivity was found in the Golgi apparatus of the maturation ameloblast. These results suggest that the 70-kDa protein, whose degradation might be very fast, is the parent protein of the 27- and 29-kDa proteins.

Immunocytochemical and immunochemical study of enamelins, using antibodies against porcine 89-kDa enamelin and its N-terminal synthetic peptide, in porcine tooth germs

Abstract Enamelins comprise an important family of the enamel matrix proteins. Porcine tooth germs were investigated immunochemically and immunocytochemically using two antibodies: a polyclonal antibody raised against the porcine 89-kDa enamelin (89 E) and an affinity purified anti-peptide antibody against the porcine enamelin amino-terminus (EN). Immunochemical analysis of layers of immature enamel from the matrix formation stage detected immunopositive protein bands ranging from 10 kDa to 155 kDa in the outer layer enamel sample irrespective of the antibodies used. In contrast, the middle and inner enamel layer mainly contained lower molecular weight enamelins. In immunocytochemical analyses of the differentiation stage, 89 E stained enamel matrix islands around mineralized collagen fibrils of dentin, while EN stained both enamel matrix islands and stippled material. At the matrix formation stage, both antibodies intensely stained enamel prisms located in the outer layer. In the inner layer, 89 E moderately stained enamel matrix homogeneously, while EN primarily stained the prism sheath. The intense immunoreaction over the surface layer of enamel matrix at the matrix formation stage, following staining with 89 E and EN, disappeared by the end of the transition stage and the early maturation stage, respectively. The Golgi apparatus and secretory granules in the ameloblasts from the late differentiation stage to the transition stage were immunostained by both antibodies. These results suggest that expression of enamelin continues from late differentiation to the transition stage and the cleavage of N-terminal region of enamelin occurs soon after secretion. Some enamelin degradation products, which apparently have no affinity for hydroxyapatite crystals, concentrate in the prism sheaths during enamel maturation.

Maturation ameloblasts of the porcine tooth germ do not express amelogenin.

Abstract Amelogenins are the most abundant constituent in the enamel matrix of developing teeth. Recent investigations of rodent incisors and molar tooth germs revealed that amelogenins are expressed not only in secretory ameloblasts but also in maturation ameloblasts, although in relatively low levels. In this study, we investigated expression of amelogenin in the maturation stage of porcine tooth germs by in situ hybridization and immunocytochemistry. Amelogenin mRNA was intensely expressed in ameloblasts from the differentiation to the transition stages, but was not detected in maturation stage ameloblasts. C-terminal specific anti-amelogenin antiserum, which only reacts with nascent amelogenin molecules, stained ameloblasts from the differentiation to the transition stages. This antiserum also stained the surface layer of immature enamel at the same stages. At the maturation stage, no immunoreactivity was found within the ameloblasts or the immature enamel. These results indicate that, in porcine tooth germs, maturation ameloblasts do not express amelogenins, suggesting that newly secreted enamel matrix proteins from the maturation ameloblast are not essential to enamel maturation occurring at the maturation stage.

The sites of origin and termination of afferent and efferent components in the lingual and pharyngeal branches of the glossopharyngeal nerve in the Japanese monkey (Macaca fuscata)

Afferent and efferent components in the lingual and pharyngeal branches of the glossopharyngeal nerve (Li and Ph) of the Japanese monkey (Macaca fuscata) were examined. After injecting wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) unilaterally into the central cut end of the Li and Ph, or into the stylopharyngeal muscle, labeled neuronal cell bodies and terminal labeling were observed in the medulla oblongata, peripheral ganglia of the glossopharyngeal and vagus nerves, and cervical ganglia of the sympathetic trunk. The following conclusions were deduced from the results. The Li contains efferent fibers from the inferior salivatory nucleus, and superior cervical ganglion. The afferent fibers in the Li are composed mainly of peripheral processes of ganglion neurons in the superior and petrous ganglia of the glossopharyngeal nerve, and additionally of those of ganglion neurons in the jugular ganglion of the vagus nerve. The afferent fibers in the Li terminate mainly in the lateral division of the nucleus of the solitary tract, and additionally in the dorsal aspect of the lateral marginal region of the interpolar spinal trigeminal nucleus. The Ph is mainly composed of efferent fibers from the ambiguous nucleus and superior cervical ganglion; only a small number of afferent fibers from the sensory ganglia of the glossopharyngeal and vagus nerves are contained in the Ph. Stylopharyngeal motoneurons are distributed in the retrofacial part of the ambiguous nucleus.