Tissue-specific analysis of Fgf18 gene function in palate development.

BACKGROUND: Previous studies showed that mice lacking Fgf18 function had cleft palate defects and that the FGF18 locus was associated with cleft lip and palate in humans, but what specific roles Fgf18 plays during palatogenesis are unclear. RESULTS: We show that Fgf18 exhibits regionally restricted expression in developing palatal shelves, mandible, and tongue, during palatal outgrowth and fusion in mouse embryos. Tissue-specific inactivation of Fgf18 throughout neural crest-derived craniofacial mesenchyme caused shortened mandible and reduction in ossification of the frontal, nasal, and anterior cranial base skeletal elements in Fgf18c/c ;Wnt1-Cre mutant mice. About 64% of Fgf18c/c ;Wnt1-Cre mice exhibited cleft palate. Whereas palatal shelf elevation was impaired in many Fgf18c/c ;Wnt1-Cre embryos, no significant difference in palatal cell proliferation was detected between Fgf18c/c ;Wnt1-Cre embryos and their control littermates. Embryonic maxillary explants from Fgf18c/c ;Wnt1-Cre embryos showed successful palatal shelf elevation and fusion in organ culture similar to the maxillary explants from control embryos. Furthermore, tissue-specific inactivation of Fgf18 in the early palatal mesenchyme did not cause cleft palate. CONCLUSION: These results demonstrate a critical role for Fgf18 expression in the neural crest-derived mesenchyme for the development of the mandible and multiple craniofacial bones but Fgf18 expression in the palatal mesenchyme is dispensable for palatogenesis.

Cis-control of Six1 expression in neural crest cells during craniofacial development.

BACKGROUND: Six1 is a transcriptional factor that plays an important role in embryonic development. Mouse and chick embryos deficient for Six1 have multiple craniofacial anomalies in the facial bones and cartilages. Multiple Six1 enhancers have been identified, but none of them has been reported to be active in the maxillary and mandibular process. RESULTS: We studied two Six1 enhancers in the chick neural crest tissues during craniofacial development. We showed that two evolutionarily conserved enhancers, Six1E1 and Six1E2, act synergistically. Neither Six1E1 nor Six1E2 alone can drive enhancer reporter signal in the maxillary or mandibular processes. However, their combination, Six1E, showed robust enhancer activity in these tissues. Similar reporter signal can also be driven by the mouse homolog of Six1E. Mutations of multiple conserved transcriptional factor binding sites altered the enhancer activity of Six1E, especially mutation of the LIM homeobox binding site, dramatically reduced the enhancer activity, implying that the Lhx protein family be an important regulator of Six1 expression. CONCLUSION: This study, for the first time, described the synergistic activation of two Six1 enhancers in the maxillary and mandibular processes and will facilitate more detailed studies of the regulation of Six1 in craniofacial development.

Altered tooth morphogenesis after silencing the planar cell polarity core component, Vangl2.

Vangl2, one of the core components of the planar cell polarity (PCP) pathway, has an important role in the regulation of morphogenesis in several tissues. Although the expression of Vangl2 has been detected in the developing tooth, its role in tooth morphogenesis is not known. In this study, we show that Vangl2 is expressed in the inner dental epithelium (IDE) and in the secondary enamel knots (SEKs) of bell stage tooth germs. Inhibition of Vangl2 expression by siRNA treatment in in vitro-cultured tooth germs resulted in retarded tooth germ growth with deregulated cell proliferation and apoptosis. After kidney transplantation of Vangl2 siRNA-treated tooth germs, teeth were observed to be small and malformed. We also show that Vangl2 is required to maintain the proper pattern of cell alignment in SEKs, which maybe important for the function of SEKs as signaling centers. These results suggest that Vangl2 plays an important role in the morphogenesis of teeth.

Alx1 Deficient Mice Recapitulate Craniofacial Phenotype and Reveal Developmental Basis of ALX1-Related Frontonasal Dysplasia.

Loss of ALX1 function causes the frontonasal dysplasia syndrome FND3, characterized by severe facial clefting and microphthalmia. Whereas the laboratory mouse has been the preeminent animal model for studying developmental mechanisms of human craniofacial birth defects, the roles of ALX1 in mouse frontonasal development have not been well characterized because the only previously reported Alx1 mutant mouse line exhibited acrania due to a genetic background-dependent failure of cranial neural tube closure. Using CRISPR/Cas9-mediated genome editing, we have generated an Alx1-deletion mouse model that recapitulates the FND craniofacial malformations, including median orofacial clefting and disruption of development of the eyes and alae nasi. In situ hybridization analysis showed that Alx1 is strongly expressed in frontonasal neural crest cells that give rise to periocular and frontonasal mesenchyme. Alx1 del/del embryos exhibited increased apoptosis of periocular mesenchyme and decreased expression of ocular developmental regulators Pitx2 and Lmxb1 in the periocular mesenchyme, followed by defective optic stalk morphogenesis. Moreover, Alx1 del/del embryos exhibited disruption of frontonasal mesenchyme identity, with loss of expression of Pax7 and concomitant ectopic expression of the jaw mesenchyme regulators Lhx6 and Lhx8 in the developing lateral nasal processes. The function of ALX1 in patterning the frontonasal mesenchyme is partly complemented by ALX4, a paralogous ALX family transcription factor whose loss-of-function causes a milder and distinctive FND. Together, these data uncover previously unknown roles of ALX1 in periocular mesenchyme development and frontonasal mesenchyme patterning, providing novel insights into the pathogenic mechanisms of ALX1-related FND.

Sox2 maintains epithelial cell proliferation in the successional dental lamina.

OBJECTIVES: The successional dental lamina is the distinctive structure on the lingual side of the vertebrate tooth germ. The aim of this study was to investigate the relationship among Sox2, Claudin10 and laminin5 and the role of Sox2 in successional dental lamina proliferation during vertebrate tooth development. MATERIALS AND METHODS: To understand the successional dental lamina, two types of successional tooth formation, that in geckos (with multiple rounds of tooth generation) and that in mice (with only one round of tooth generation), were analysed. RESULTS: Unique coexpression patterns of Sox2 and Claudin10 expression were compared in the successional dental lamina from the cap stage to the late bell stage in the mouse tooth germ and in juvenile gecko teeth to support continuous tooth replacement. Furthermore, Laminin5 expression was shown in the cap stage and decreased after the bell stage. Upon comparing the epithelial cell cycles and cell proliferation in successional dental lamina regions between mouse and gecko molars using BrdU and IdU staining and pulse-chase methods, distinctive patterns of continuous expression were revealed. Moreover, Sox2 overexpression with a lentiviral system resulted in hyperplastic dental epithelium in mouse molars. CONCLUSIONS: Our findings indicate that the regulation of Sox2 in dental lamina proliferation is fundamental to the successional dental lamina in both species.

Comparison of biofilm formation and migration of Streptococcus mutans on tooth roots and titanium miniscrews.

Periodontitis and peri-implantitis are inflammatory diseases caused by periodontal pathogenic bacteria leading to destruction of supporting periodontal/peri-implant tissue. However, the progression of inflammatory process of these two diseases is different. The bacterial biofilm is the source of bacteria during the inflammatory process. As the bacteria migrate down the surface of tooth or titanium implant, the inflammation spreads along with it. Streptococcus mutans has an important role in oral bacterial biofilm formation in early stage biofilm before the microbiota shift to late stage and become more virulent. The other major difference is the existence of periodontal ligament (PDL) cells in normal teeth but not in peri-implant tissue. This study aims to compare the S. mutans bacterial biofilm formation and migration on 2 different surfaces, tooth root and titanium miniscrew. The biofilm was grown with a flow cells system to imitate the oral dynamic system with PDL cells. The migration distances were measured, and the biofilm morphology was observed. Data showed that the biofilm formation on miniscrew was slower than those on tooth root at 24 hr. However, there were no difference in the morphology of the biofilm formed on the tooth root with those formed on the miniscrew at both 24 and 48 hr. The biofilm migration rate was significantly faster on miniscrew surface compare with those on tooth root when observe at 48 hr (p < .001). There are no significant differences in biofilm migration within miniscrew group and tooth root group despite the exiting of PDL cell (p > .05). The biofilm's migration rate differences on various surfaces could be one of the factors accounting for the different inflammatory progression between periodontitis and peri-implantitis disease.