3D approaches for stem cell niches in medaka pharyngeal dentition

Stem cell population exists in “niches” in various tissues. Identification and characterization of stem-cell niches are essential for understanding stem cell maintenance and tissue and organ regeneration. Medaka, a small-sized teleosts fish, has as many as 1000 functional teeth in the pharyngeal cavity. These teeth are known to be replaced throughout life thus implicating existence of large population of odontogenic stem cells in pharyngeal regions of Medaka. Objectives: and Methods: Here we report our new observations of possible stem cell niches in the adult Medaka pharyngeal dentition, by means of histological, BrdU labeling, and calcein labeling studies combined with three-D reconstruction and viewing methods. Results: & Discussion: Histological three-D reconstruction of pharyngeal regions revealed that, in adult medaka pharyngeal dentition, functional teeth and tooth germs of their replacement teeth are organized in families of successional tooth organs, each comprising up to five generations of teeth. In vivo calcein labeling studies have confirmed that the replacement cycle of pharyngeal teeth of adult Medaka is around 6 W since the labeled tooth germs posterior to the rows of functional teeth replace the functional teeth in 2 W, and remain functional for the following 2 to 3 W until they are being replaced by the next generation of teeth. Long-term BrdU label-chase studies of adult Medaka up to 12 W allowed localization of the groups of label-retaining cells near the youngest tooth germs in each family of growing tooth organs. Conclusions: These data clearly demonstrated spatial-temporal arrangements of families of pharyngeal tooth organs, confirmed their replacement cycles, and further identified possible sites of stem cell niches in Medaka pharyngeal dentition. This work was supported in part by JSPS grants for scientific research (2122103) and G-COE Program, International Research Center for Molecular Science in Tooth and Bone Diseases.