PMID:15604101

Citation	Kettunen, P, Løes, S, Furmanek, T, Fjeld, K, Kvinnsland, IH, Behar, O, Yagi, T, Fujisawa, H, Vainio, S, Taniguchi, M and Luukko, K (2005) Coordination of trigeminal axon navigation and patterning with tooth organ formation: epithelial-mesenchymal interactions, and epithelial Wnt4 and Tgfbeta1 regulate semaphorin 3a expression in the dental mesenchyme. Development 132:323-34
Abstract	During development, trigeminal nerve fibers navigate and establish their axonal projections to the developing tooth in a highly spatiotemporally controlled manner. By analyzing Sema3a and its receptor Npn1 knockout mouse embryos, we found that Sema3a regulates dental trigeminal axon navigation and patterning, as well as the timing of the first mandibular molar innervation, and that the effects of Sema3a appear to be mediated by Npn1 present in the axons. By performing tissue recombinant experiments and analyzing the effects of signaling molecules, we found that early oral and dental epithelia, which instruct tooth formation, and epithelial Wnt4 induce Sema3a expression in the presumptive dental mesenchyme before the arrival of the first dental nerve fibers. Later, at the bud stage, epithelial Wnt4 and Tgfbeta1 regulate Sema3a expression in the dental mesenchyme. In addition, Wnt4 stimulates mesenchymal expression of Msx1 transcription factor, which is essential for tooth formation, and Tgfbeta1 proliferation of the dental mesenchymal cells. Thus, epithelial-mesenchymal interactions control Sema3a expression and may coordinate axon navigation and patterning with tooth formation. Moreover, our results suggest that the odontogenic epithelium possesses the instructive information to control the formation of tooth nerve supply.
Links	PubMed Online version:10.1242/dev.01541
Keywords	Animals; Axons/metabolism; Body Patterning; Cell Proliferation; Epithelium/metabolism; Gene Expression Regulation, Developmental; Glial Cell Line-Derived Neurotrophic Factor; Imaging, Three-Dimensional; Immunohistochemistry; In Situ Hybridization; Mesoderm/metabolism; Mice; Mice, Knockout; Mice, Transgenic; Models, Biological; Nerve Growth Factor/biosynthesis; Nerve Growth Factors/biosynthesis; Proto-Oncogene Proteins/metabolism; Rats; Semaphorin-3A/biosynthesis; Time Factors; Tissue Distribution; Tooth/embryology; Tooth/innervation; Transforming Growth Factor beta/metabolism; Transforming Growth Factor beta1; Trigeminal Nerve/physiology; Wnt Proteins; Wnt4 Protein
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