Dmp1 Knock-in Mice Faithfully Report and Manipulate Dmp1-Expressing Cells

Dentin, the primary structural component of teeth, is a mineralized tissue formed by odontoblasts, which strongly express the Dmp1 gene. Dmp1 is also expressed in osteocytes, making it a valuable marker for studying bone biology and diseases. Transgenic mouse lines expressing Cre, CreER, or fluorescent reporters such as GFP under the control of 8-kb or 10-kb Dmp1 promoters have been widely used to investigate gene functions in odontoblasts and osteocytes. However, the transgenic models exhibit ectopic expression, and reporter signals are often reduced in mature odontoblasts, limiting their utility for lineage tracing and studies of terminal differentiation. To address these limitations, we generated 2 novel knock-in mouse lines, Dmp1^CreERT2 and Dmp1^ZsGreen, using CRISPR-Cas9-mediated genome editing. In both models, an internal ribosome entry site (IRES)-CreERT2 or IRES-ZsGreen cassette was inserted into the 3' untranslated region (UTR) of the endogenous Dmp1 locus. This design preserves normal Dmp1 expression while permitting robust, Dmp1-specific expression of CreERT2 or ZsGreen in odontoblasts and cementoblast/cementocytes. By maintaining endogenous regulatory control, these knock-in lines eliminate the ectopic transgene expression commonly observed in transgenic mice generated by injecting the promoter-driven constructs. The Dmp1^ZsGreen line enables direct visualization of Dmp1-expressing odontoblasts and cementoblasts/cementocytes, while the Dmp1^CreERT2 line allows inducible genetic manipulation in these cells in vivo. Together, these models provide faithful tools for investigating the cellular and molecular mechanisms regulating dentinogenesis and osteocyte biology, as well as for studying dental and alveolar bone tissues, with potential applications in craniofacial biology.