Teeth develop from interactions between embryonic oral epithelium and neural-crest-derived mesenchyme. These cells can be separated into singlecell populations and recombined to form normal teeth, providing a basis for bioengineering new teeth if suitable, non-embryonic cell sources can be identified. We show here that cells can be isolated from adult human gingival tissue that can be expanded in vitro and, when combined with mouse embryonic tooth mesenchyme cells, form teeth. Teeth with developing roots can be produced from this cell combination following transplantation into renal capsules. These bioengineered teeth contain dentin and enamel with ameloblast-like cells and rests of Malassez of human origin.

Polycystin 2 (Pkd2), which belongs to the transient receptor potential family, plays a critical role in development. Pkd2 is mainly localized in the primary cilia, which also function as mechanoreceptors in many cells that influence multiple biological processes including Ca(2+) influx, chemical activity and signalling pathways. Mutations in many cilia proteins result in craniofacial abnormalities. Orofacial tissues constantly receive mechanical forces and are known to develop and grow through intricate signalling pathways. Here we investigate the role of Pkd2, whose role remains unclear in craniofacial development and growth. In order to determine the role of Pkd2 in craniofacial development, we located expression in craniofacial tissues and analysed mice with conditional deletion of Pkd2 in neural crest-derived cells, using Wnt1Cre mice. Pkd2 mutants showed many signs of mechanical trauma such as fractured molar roots, distorted incisors, alveolar bone loss and compressed temporomandibular joints, in addition to abnormal skull shapes. Significantly, mutants showed no indication of any of these phenotypes at embryonic stages when heads perceive no significant mechanical stress in utero. The results suggest that Pkd2 is likely to play a critical role in craniofacial growth as a mechanoreceptor. Pkd2 is also identified as one of the genes responsible for autosomal dominant polycystic kidney disease (ADPKD). Since facial anomalies have never been identified in ADPKD patients, we carried out three-dimensional photography of patient faces and analysed these using dense surface modelling. This analysis revealed specific characteristics of ADPKD patient faces, some of which correlated with those of the mutant mice.

Background: Tooth development is known to be mediated by the cross-talk between signaling pathways, including Shh, Fgf, Bmp, and Wnt. MicroRNAs (miRNAs) are 19-to 25-nt noncoding small singlestranded RNAs that negatively regulate gene expression by binding target mRNAs, which is believed to be important for the fine-tuning signaling pathways in development. To investigate the role of miRNAs in tooth development, we examined mice with either mesenchymal (Wnt1Cre/Dicer fl/fl ) or epithelial (ShhCre/Dicer fl/fl ) conditional deletion of Dicer, which is essential for miRNA processing. Results: By using a CD1 genetic background for Wnt1Cre/Dicer fl/fl , we were able to examine tooth development, because the mutants retained mandible and maxilla primordia. Wnt1Cre/Dicer fl/fl mice showed an arrest or absence of teeth development, which varied in frequency between incisors and molars. Extra incisor tooth formation was found in ShhCre/Dicer fl/fl mice, whereas molars showed no significant anomalies. Microarray and in situ hybridization analysis identified several miRNAs that showed differential expression between incisors and molars. Conclusion: In tooth development, miRNAs thus play different roles in epithelium and mesenchyme, and in incisors and molars. Developmental Dynamics 241:1465-1472, 2012. V C 2012 Wiley Periodicals, Inc.Key words: microRNA; Dicer; tooth development; Wnt1Cre; ShhCre; epithelial-mesenchymal interaction Key findings:Extra incisor tooth formation was found in ShhCre/Dicer fl/fl mice. Wnt1Cre/Dicer fl/fl mice showed an arrest or absence of teeth development, which varied in frequency between incisors and molars. Microarray an in situ hybridization analysis identified several miRNAs that showed differential expression between incisors and molars.