Odontogenic Stem Cells in Pharyngeal Dentition of Teleost Fish Medaka

Small-sized fresh-water teleost fish medaka, Oryzias Latipes, has ideal features for the study of embryogenesis and organogenesis owing to their compact size, short embryonic period, rapid growth speed and body transparency. Medaka is particularly suitable to investigate tooth growth and replacement, since adult medaka has as many as 1000 functional teeth in the pharyngeal dentition being continuously replaced throughout life.

Objectives: The objective of current study is to identify and locate possible stem cell niches in the pharyngeal dentition of medaka, which appear to serve as excellent source of odontogenic stem cells for the study of tooth development and regeneration.

 Methods: The upper and lower pharyngeal dentition of adult medaka with or without fluorochrome- or short-and long term-BrdU-labeling were collected and processed for histological, histomorphometrical, and 3D reconstruction studies.

Results: Current data clearly indicated that functional teeth and their successional tooth germs were organized in families up to five generations being aligned at some angles with respect to parasagittal planes on each pharyngeal bone.  In vivo calcein and alizarin complexon labeling studies confirmed the replacement cycle of pharyngeal teeth being around 6W in adults and shorter in younger ones.  3D reconstruction of BrdU labeling at various time intervals in adult medaka up to 12W-chase confirmed existence of groups of label-retaining cells posterior to the youngest tooth germ in each tooth family.

Conclusions:  Pharyngeal teeth and successional tooth germs comprise well-aligned families of tooth organs, in which stem cell niches are located immediately posterior to the youngest tooth germ in each family.