Histological Study of Genesis of the Mice Oral Vestibule

Abstract

Background: Both the vestibular lamina (VL) and dental lamina (DL) develop from the primary epithelial band of the oral cavity. Previous studies have reported that VL and DL were initiated by certain epithelial-mesenchymal interactions between the primary epithelial band of the oral cavity and underlying mesenchyme; however, the exact mechanisms remain to be elucidated. Aims: Here we studied how the retinoblastoma (Rb) family and E2 promoter binding factor (E2F) regulate signals that control and regulate the proliferation and differentiation of the VL leading to the formation of the oral vestibule. Methods: Immunohistochemical light microscopy by the enhanced polymer one-step staining(EPOS) method and confocal laser scanning microscopy by the LsAB labelled streptavidin biotin (LSAB) method were performed on the developing vestibular lamina(VL) of fetal mice at stages from 11 days after fertilization E11 to E14.The immunohistochemical findings were compared with the findings in the developing dental lamina (DL) and tooth germ. Conventional transmission electron microscopy was performed on the E13 fetuses, in an effort to elucidate the differentiation of keratocytes in the developing VL. Results: We found that: 1) EGF, TGF , EGFR, PCNA, FGF2, pRb, and FGFR1-4 were immunolocalized in the developing tissues. 2) Cytokine expression patterns indicated that the EGF family and FGF2 essentially induced VL generation and cell proliferation. 3) FGFR1 as diffusely localized in the primary epithelial band, but was strongly expressed in the E12-14 VL and DL/enamel organ. By contrast, EGFR internalization was observed in the differentiating E13 VL. 4) Expression of pRb was intensely localized in the suprabasal layer of the E13 VL corresponding to CK-10 expression and keratohyaline-containing structures in the VL stratum germinativum cells. Conclusions: We suggest a mechanism in which FGFR1 regulates pRb to induce proliferation of cells in the VL and DL/enamel organ, and, in particular, to incite keratocyte differentiation and subsequent exfoliation of keratinizing VL cells.