library_construction_protocol: Mandibles were collected from C57BL/6J mice at P25. After removing the soft tissues, samples were fixed overnight with RNase-free 4% PFA . Samples were decalcified with RNase-free 0.5 M EDTA for 3 days. Decalcified samples were cryoprotected in 30% sucrose/PBS solutions and then in 30% sucrose/PBS: OCT (1:1) solutions, each for at least overnight at 4 °C. Samples were embedded in an OCT compound under a stereomicroscope and transferred on a sheet of dry ice to solidify the compound. The library preparation followed the protocol (CG000685). The quality of the final libraries was examined using the Agilent High-Sensitivity DNA Kit (#5067-4626) by Agilent Bioanalyzer 2100 (Agilent Technologies, Santa Clara, USA). The qualified libraries were sequenced using the paired-end sequencing on an Illumina NovaSeq X Plus (Illumina, Inc., USA)