| Research Abstract |
The OASIS gene was cloned from long term-cultured astrocytes and found to encode a putative transcription factor belonging to the camp responsive element binding protein gene family. The OASIS was expressed primarily in the tooth germs, salivary gland, cartilages and epithelium of the digestive tract in mouse embryos, and was increasingly expressed in the nervous system during the postnatal development. In the present study, we examined in detail the temporospatial distribution of OASIS mRNA expression in the mouse tooth germs. Oro-facial tissue of embryonic days 11(E11) to postnatal day 1 (P1) mice were fixed with 4% paraformaldehyde and embedded in paraffin. In situ hybridization was performed with a digoxigenin-labeled RNA probe. In the tooth germs of molar and incisor of E14 mice, a positive signal for OASIS mRNA was firstly detected in the inner enamel epithelium of the enamel organ, but no signal was detectable in other types cells. In El6 mice, the gene was expressed in the inne
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r enamel epithelium of the maxillary first molar exclusively, and in the inner enamel epithelium at the apical loop and in the preodontoblasts at incisal portion of the mandibular incisor tooth germ. In E18 mice, the gene was expressed in the entire inner enamel epithelium and in the preodontoblasts of central cusp, but weakly in the cervical loop in the tooth germ of maxillary first molar. In the incisor tooth germ of E18 mice the signal of the inner enamel epithelium remained weakly only at the bulbous part of the apical loop, but not detected in the ameloblats. In P1 mice, the gene was slightly expressed in the inner enamel epithelium near the cervical loop and the preodontoblasts from late bell stage tooth germs of maxillary first molar. In the incisor tooth germ of P1 mice, the gene was expressed in the inner enamel epithelium near the bulbous part of the apical loop and the preodontoblasts. In the tooth germs of molar and incisor of P1 mice, the gene was not expressed in the preameloblasts neither of molar nor incisor, precursor cells of the preodontoblasts, the mature odontoblasts, the inner enamel epithelium, the preameloblasts, and the ameloblasts. After the disappearance of the signal in the inner enamel epithelium, signal was detected exclusively in preodontoblasts and absent in other ectodermal and mesenchymal cells including amelobiasts and odontoblasts, suggesting that the gene plays an important role in the differentiation of odontoblasts. The results revealed that the OASIS geae showed a characteristic temporospatial expression pattern in the mouse tooth germs, indicating that the gene is involved in the tooth development. Less
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