Chick Tooth Induction Revisited JINGLEI CAI 1 , SUNG-WON CHO 1 , MIKIO ISHIYAMA 2 , MASATO MIKAMI 3 , AKIHIRO HOSOYA 4 , YUKISHIGE KOZAWA 5 , HAYATO OHSHIMA 6 , AND HAN-SUNG JUNG 1Ã 1 Division in Anatomy and Developmental Biology, Department of Oral Biology, Research Center for Orofacial Hard Tissue Regeneration, Brain Korea 21 project, Oral Science Research Center, College of Dentistry, Yonsei Center of Biotechnology, Yonsei University, Seoul, Korea 2 Department of Histology, The Nippon Dental University School of Life Dentistry at Niigata, Niigata, Japan 3 Department of Microbiology, The Nippon Dental University School of Life Dentistry at Niigata, Niigata, Japan 4 Department of Oral Histology, Matsumoto Dental University, Shiojiri, Nagano, Japan 5 Department of Anatomy (Division II), Nihon University School of Dentistry, Tokyo, Japan 6 Division of Anatomy and Cell Biology of the Hard Tissue, Department of Tissue Regeneration and Reconstruction, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan ABSTRACT Teeth have been missing from Aves for almost 100 million years. However, it is believed that the avian oral epithelium retains the molecular signaling required to induce odontogenesis, and this has been widely examined using heterospecific recombinations with mouse dental mesenchyme. It has also been argued that teeth can form from the avian oral epithelium owing to contamination of the mouse mesenchyme with mouse dental epithelial cells. To investigate the possibility of tooth formation from chick oral epithelium and the characteristics of possible chick enamel, we applied LacZ transgenic mice during heterospecific recombination and examined the further tooth formation. Transmission electron microscopy was used to identify the two tissues during development after heterospecific recombination. No mixing was detected between chick oral epithelium and mouse dental mesenchyme after 2 days, and secretory ameloblasts with Tomes’ processes were observed after 1 week. Teeth were formed after 3 weeks with a single cusp pattern, possibly determined by epithelial factors, which is similar to that of the avian tooth in the late Jurassic period. These recombinant teeth were smaller than mouse molars, whereas perfect structures of both ameloblasts and enamel showed histological characteristics similar to those of mice. Together these observations consistent with previous report that odontogenesis is initially directed by species-specific mesenchymal signals interplaying with common epithelial signals. J. Exp. Zool. (Mol. Dev. Evol.) 312B:465– 472, 2009. r 2009 Wiley-Liss, Inc. How to cite this article: Cai J, Cho S-W, Ishiyama M, Mikami M, Hosoya A, Kozawa Y, Ohshima H, Jung H-S. 2009. Chick tooth induction revisited. J. Exp. Zool. (Mol. Dev. Evol.) 312B:465–472. Tooth development in mammals and other vertebrates involves a complex sequence of epithe- lial mesenchymal interactions, resulting in a progressive specification of odontogenesis (Pispa and Thesleff, 2003). Classical studies have demon- strated that specific molecules function at parti- cular steps in odontogenesis (Vainio et al., ’93; Satokata and Maas, ’94; Neubuser et al., ’97; Published online 18 February 2009 in Wiley InterScience (www. interscience.wiley.com). DOI: 10.1002/jez.b.21265 Received 13 November 2008; Accepted 17 November 2008 Grant sponsor: Korea Science and Engineering Foundation (KOSEF); Grant number: M10646010001-08N4601-00110. Additional supporting information may be found in the online version of this article. Ã Correspondence to: Han-Sung Jung, Department of Oral Biology, College of Dentistry, Yonsei University, 134 Shinchon-Dong, Seodae- moon-Gu, Seoul 120-752, Korea. E-mail: hsjung@yuhs.ac r 2009 WILEY-LISS, INC. JOURNAL OF EXPERIMENTAL ZOOLOGY (MOL DEV EVOL) 312B:465–472 (2009)