Expression of secretory calcium-binding phosphoprotein (scpp) genes in medaka during the formation and replacement of pharyngeal teeth

<jats:title>Abstract</jats:title><jats:sec> <jats:title>Background</jats:title> <jats:p>Analyses of tooth families and tooth-forming units in medaka with regard to tooth replacement cycles and the localization of odontogenic stem cell niches in the pharyngeal dentition clearly indicate that continuous tooth replacement is maintained. The <jats:italic>secretory calcium-binding phosphoprotein</jats:italic> (<jats:italic>scpp</jats:italic>) gene cluster is involved in the formation of mineralized tissues, such as dental and bone tissues, and the genes encoding multiple SCPPs are conserved in fish, amphibians, reptiles, and mammals. In the present study, we examined the expression patterns of several <jats:italic>scpp</jats:italic> genes in the pharyngeal teeth of medaka to elucidate their roles during tooth formation and replacement.</jats:p> </jats:sec><jats:sec> <jats:title>Methods</jats:title> <jats:p>Himedaka (Japanese medaka, <jats:italic>Oryzias latipes</jats:italic>) of both sexes (body length: 28 to 33 mm) were used in this study. Real-time quantitative reverse transcription-polymerase chain reaction (PCR) (qPCR) data were evaluated using one-way analysis of variance for multi-group comparisons, and the significance of differences was determined by Tukey’s comparison test. The expression of <jats:italic>scpp</jats:italic> genes was examined using in situ hybridization (ISH) with a digoxigenin-labeled, single-stranded antisense probe.</jats:p> </jats:sec><jats:sec> <jats:title>Results</jats:title> <jats:p>qPCR results showed that several <jats:italic>scpp</jats:italic> genes were strongly expressed in pharyngeal tissues. ISH analysis revealed specific expression of <jats:italic>scpp1</jats:italic>, <jats:italic>scpp5</jats:italic>, and <jats:italic>sparc</jats:italic> in tooth germ, and <jats:italic>scpp5</jats:italic> was continually expressed in the odontoblasts of teeth attached to pedicles, but not in the osteoblasts of pedicles. In addition, many <jats:italic>scpp</jats:italic> genes were expressed in inner dental epithelium (ide), but not in odontoblasts, and <jats:italic>scpp2</jats:italic> consistently showed epithelial-specific expression in the functional teeth. Taken together, these data indicate that specific expression of <jats:italic>scpp2</jats:italic> and <jats:italic>scpp5</jats:italic> may play a critical role in pharyngeal tooth formation in medaka.</jats:p> </jats:sec><jats:sec> <jats:title>Conclusion</jats:title> <jats:p>We characterized changes in the expression patterns of <jats:italic>scpp</jats:italic> genes in medaka during the formation and replacement of pharyngeal teeth.</jats:p> </jats:sec>