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Tooth development is controlled by body plan during the fetal period, the generation of teeth from tooth germ is induced by the epithelial-mesenchymal interaction. Spatiotemporal regulation of tooth morphogenesis is supported by gene expression. Although many of the genes involved in tooth development are known, the molecular mechanism underlying tooth morphogenesis is not completely understood. For a comprehensive understanding of tooth development, the elucidation of unknown genes is necessary. In this study, to identify unknown genes involved in tooth development, we performed genome-wide analysis at each stage of tooth development and identified 17 genes with high levels of expression and large changes in expression. In addition, we performed qPCR and in situ hybridization analyses to elucidate the spatiotemporal regulation, such as the regulation that occurs around or in the entire tooth germ, enamel knots, epithelium, and mesenchyme. These results show that these characteristic genes may play important roles in each time period or region of tooth development, and the elucidation of the functions of these genes will lead to an integrated understanding of the process of tooth development., 博士（医学）・甲第790号・令和3年3月15日, 発行元である日本再生歯科医学会の許諾を得て登録（2021年6月29日付）, ジャーナル公式サイト（日本再生歯科医学会HP内）：http://www.jarde.jp/zasshi/e/18-2-1.html

Enchytraeus japonensis is a small oligochaete species that proliferates asexually via fragmentation and regeneration. As sexual reproduction can also be induced, it is a good model system for the study of both regenerative and germline stem cells. It has been shown by histological study that putative mesodermal stem cells called neoblasts, and dedifferentiated epidermal and endodermal cells are involved in blastema formation. To clarify the molecular biological mechanism operating at an initial stage of regeneration in E. japonensis , we isolated five genes whose expression levels changed in the regeneration process occurring between growing and early regenerating worms by cDNA subtraction method. One of the isolated genes (a novel gene named grimp ) was expressed transiently from 3 to 12 h post-amputation only in neoblasts and a population of mesodermal cells (the non-neoblast grimp-expressing cells) incorporating BrdU simultaneously showed mitotic activity. We carried out functional analysis by using RNA interference (RNAi). In knock-down worms, the number of BrdU-positive neoblasts and the non-neoblast grimp-expressing cells in the coelom drastically decreased. Also the elongation and segmentation of blastema were inhibited, while no statistically significant inhibitory effect was observed in epidermal and intestinal cells. These results suggest that grimp is required for initial proliferation of neoblasts and some mesodermal cells for regeneration. We also investigate the function of grimp at the protein level. cDNA sequence of grimp contains a putative open reading frame and poly (A). The deduced polypeptide contains a triplicate repeat of a very similar sequence containing integrin-binding RGDS sequences and protein kinase C phosphorylation sites. However, it is hard to predict its function from the sequence. Thus we took several approaches to clarify the localization and the function of grimp protein.