Expression of Set-alpha during morphogenesis of mouse lower first molar

Facioscapulohumeral muscular dystrophy (FSHD) region gene 1 (FRG1) expression and possible function in mouse tooth germ development

Abnormal expression of Facioscapulohumeral muscular dystrophy (FSHD) region gene 1 (FRG1) is involved in the pathogenesis of FSHD. FRG1 is also important for the normal muscular and vascular development. Our previous study showed that FRG1 is one of the highly expressed genes in the mandible on embryonic day 10.5 (E10.5) than on E12.0. In this study, we investigated the temporospatial expression pattern of FRG1 mRNA and protein during the development of the mouse lower first molar, and also evaluated the subcellular localization of the FRG1 protein in mouse dental epithelial (mDE6) cells. The FRG1 expression was identified in the dental epithelial and mesenchymal cells at the initiation and bud stages. It was detected in the inner enamel epithelium at the cap and early bell stages. At the late bell and root formation stages, these signals were detected in ameloblasts and odontoblasts during the formation of enamel and dentin matrices, respectively. The FRG1 protein was localized in the cytoplasm in the mouse tooth germ in vivo, while FRG1 was detected predominantly in the nucleus and faintly in the cytoplasm in mDE6 cells in vitro. In mDE6 cells treated with bone morphogenetic protein 4 (BMP4), the protein expression of FRG1 increased in cytoplasm, suggesting that FRG1 may translocate to the cytoplasm. These findings suggest that FRG1 is involved in the morphogenesis of the tooth germ, as well as in the formation of enamel and dentin matrices and that FRG1 may play a role in the odontogenesis in the mouse following BMP4 stimulation.

Itm2a expression in the developing mouse first lower molar, and the subcellular localization of Itm2a in mouse dental epithelial cells

Itm2a is a type II transmembrane protein with a BRICHOS domain. We investigated the temporospatial mRNA and protein expression patterns of Itm2a in the developing lower first molar, and examined the subcellular localization of Itm2a in murine dental epithelial (mDE6) cells. From the initiation to the bud stage, the in situ and protein signals of Itm2a were not detected in either the dental epithelial or mesenchymal cells surrounding the tooth bud. However, at the bell stage, these signals of Itm2a were primarily observed in the inner enamel epithelium of the enamel organ. After the initiation of the matrix formation, strong signals were detected in ameloblasts and odontoblasts. Itm2a showed a punctate pattern in the cytoplasm of the mDE6 cells. The perinuclear-localized Itm2a displayed a frequent overlap with the Golgi apparatus marker, GM130. A tiny amount of Itm2a was colocalized with lysosomes and endoplasmic reticulum. Minimal or no overlap between the Itm2a-EGFP signals with the other organelle markers for endoplasmic reticulum, lysosome and mitochondria used in this study noted in the cytoplasm. These findings suggest that Itm2a may play a role in cell differentiation during odontogenesis, rather than during the initiation of tooth germ formation, and may be related to the targeting of proteins associated with enamel and dentin matrices in the secretory pathway.

Induction of dental epithelial cell differentiation marker gene expression in non-odontogenic human keratinocytes by transfection with thymosin beta 4

Previous studies have shown that the recombination of cells liberated from developing tooth germs develop into teeth. However, it is difficult to use human developing tooth germ as a source of cells because of ethical issues. Previous studies have reported that thymosin beta 4 (Tmsb4x) is closely related to the initiation and development of the tooth germ. We herein attempted to establish odontogenic epithelial cells from non-odontogenic HaCaT cells by transfection with TMSB4X. TMSB4X-transfected cells formed nodules that were positive for Alizarin-red S (ALZ) and von Kossa staining (calcium phosphate deposits) when cultured in calcification-inducing medium. Three selected clones showing larger amounts of calcium deposits than the other clones, expressed PITX2, Cytokeratin 14, and Sonic Hedgehog. The upregulation of odontogenesis-related genes, such as runt-related transcription factor 2 (RUNX2), Amelogenin (AMELX), Ameloblastin (AMBN) and Enamelin (ENAM) was also detected. These proteins were immunohistochemically observed in nodules positive for the ALZ and von Kossa staining. RUNX2-positive selected TMSB4X-transfected cells implanted into the dorsal subcutaneous tissue of nude mice formed matrix deposits. Immunohistochemically, AMELX, AMBN and ENAM were observed in the matrix deposits. This study demonstrated the possibility of induction of dental epithelial cell differentiation marker gene expression in non-odontogenic HaCaT cells by TMSB4X.

Protogenin, a new member of the immunoglobulin superfamily, is implicated in the development of the mouse lower first molar

Background

Protogenin (Prtg) has been identified as a gene which is highly expressed in the mouse mandible at embryonic day 10.5 (E10.5) by a cDNA subtraction method between mandibles at E10.5 and E12.0. Prtg is a new member of the deleted in colorectal carcinoma (DCC) family, which is composed of DCC, Neogenin, Punc and Nope. Although these members play an important role in the development of the embryonic central nervous system, recent research has also shed on the non-neuronal organization. However, very little is known regarding the fetal requirement of the non-neuronal organization for Prtg and how this may be associated with the tooth germ development. This study examined the functional implications of Prtg in the developing tooth germ of the mouse lower first molar.

Results

Ptrg is preferentially expressed in the early stage of organogenesis. Prtg mRNA and protein were widely expressed in the mesenchymal cells in the mandible at E10.5. The oral epithelial cells were also positive for Prtg. The expression intensity of Prtg after E12.0 was markedly reduced in the mesenchymal cells of the mandible, and was restricted to the area where the tooth bud was likely to be formed. Signals were also observed in the epithelial cells of the tooth germ. Weak signals were observed in the inner enamel epithelial cells at E16.0 and E18.0. An inhibition assay using a hemagglutinating virus of Japan-liposome containing Prtg antisense-phosphorothioated-oligodeoxynucleotide (AS-S-ODN) in cultured mandibles at E10.5 showed a significant growth inhibition in the tooth germ. The relationship between Prtg and the odontogenesis-related genes was examined in mouse E10.5 mandible, and we verified that the Bmp-4 expression had significantly been decreased in the mouse E10.5 mandible 24 hr after treatment with Prtg AS-S-ODN.

Conclusion

These results indicated that the Prtg might be related to the initial morphogenesis of the tooth germ leading to the differentiation of the inner enamel epithelial cells in the mouse lower first molar. A better understanding of the Prtg function might thus play a critical role in revealing a precious mechanism in tooth germ development.

In situ expression of ribosomal protein L21 in developing tooth germ of the mouse lower first molar

We previously performed cDNA subtraction between the mouse mandibles at embryonic day 10.5 (E10.5) in the pre-initiation stage of the odontogenesis and E12.0 in the late initiation stage to investigate the key regulator genes in odontogenesis. Ribosomal protein L21 (Rpl21) is one of differentially expressed genes in the E12.0 mandible. This study examined the precise expression pattern of Rpl21 mRNA in the mouse mandibular first molar by in situ hybridization. Rpl21 mRNA was expressed in the presumptive dental epithelium and the underlying mesenchyme at E10.5, and in the thickened dental epithelium at E12.0. Strong in situ signals were observed in the epithelial bud at E14.0, and in the enamel organ at E15.0. However, either no (E14.0) or only a weak (E15.0) in situ signal was found in the primary enamel knot at these gestational days. Rpl21 was strongly expressed in the inner enamel epithelium, cervical loop and dental lamina from E16.0 to E18.0. In addition, Rpl21 mRNA was also demonstrated in various developing cranio-facial organs. These results suggest that Rpl21 participates in the synthesis of various polypeptides which might be related to the initiation and the development of such tooth germ, and also in the synthesis of enamel components in the presecretory stage of the ameloblast. Rpl21 for protein synthesis might also be related to the morphogenesis of the developing cranio-facial organs.

Functional implication of nucleolin in the mouse first molar development

We examined the functional implication of nucleolin in the mouse first molar development. Both the nucleolin mRNA and protein expressions were demonstrated in the odontogenic epithelial cells in the early stage and in the inner enamel epithelial layer in the late stage. The expression pattern of nucleolin corresponded to the proliferating cells in the tooth germ, thus showing that nucleolin could possibly be related to cell proliferation. No in situ signal of nucleolin was found in the primary enamel knot (PEK). Furthermore, nucleolin protein was demonstrated in the PEK by immunohistochemistry. The existence of nucleolin protein in the PEK may possibly be related to the apoptosis in the PEK cells. An inhibition assay using the hemagglutinating virus of Japan-liposome containing nucleolin antisense phosphorothioated oligonucleotide (AS S-ODN) in cultured mouse mandibles at embryonic day (E) 11.0 showed a marked growth inhibition of tooth germ. Moreover, no developmental arrest was found in the cultured tooth germ at E15.0 treated with nucleolin AS S-ODN. Real time PCR was performed to examine the mRNA expression of nucleolin-related genes, and a significant reduction in the midkine mRNA expression was thus observed in the mouse mandible after being treated with nucleolin AS S-ODN. This inhibition assay indicated that nucleolin could thus be involved in the early stage of tooth germ initiation and morphogenesis, possibly by regulating the midkine expression.

Possible functional involvement of thymosin beta 4 in developing tooth germ of mouse lower first molar

We examined the detailed in situ expression pattern of thymosin beta 4 (Tbeta4) in the developing mouse mandibular first molar. Tbeta4 mRNA was expressed in the presumptive dental epithelium at embryonic day 10.5 (E10.5) and in the thickened dental epithelium at E12. An in situ signal was observed in the invaginated epithelial bud at E13, in the enamel organ at E14 and E14.5, and in the primary enamel knot (PEK) at E14.5. The signal was localized in the epithelial cells of the outer layer of the enamel organ at E15 and E15.5. No signal was found in the PEK at these stages. Tbeta4 mRNA was expressed in the inner enamel epithelium, cervical loop and dental lamina at E16 and E17. The expression of Tbeta4 mRNA was observed in the polarized inner epithelial cells at E18, newborn day 1 (N1) and N2. However, the signal intensity decreased markedly at N3. We herein report for the first time that Tbeta4 is distinctly expressed in developing tooth germ, and it may also play functional roles in the initiation, growth and differentiation of tooth germ.