The GFP-positive anterior palatal shelves were isolated from E12.5 Wnt1Cre;Meis2f/+;R26RmTmG and Wnt1Cre;Meis2f/f;R26RmTmG embryos. Samples were subjected to digestion by a cocktail of 0.02% collagenase I, II and IV in HBSS for 30min, followed by Accutase solution (Sigma) treatment for 5 min at 37℃. After stop of the digestion with culture medium containing 10% fetal bovine serum (FBS), cells were washed with PBS containing 3% FBS and then filtered through a 70- μm filter. Suspended cells were sorted by Fluorescence-activated Cell Sorting (FACS) on a BD FACS Aria Fusion cell sorter (Becton- Dickinson). Around 50,000 single GFP-positive cells from each group were obtained and were subjected promptly to generation of ATAC-seq library with the Nextera DNA Library Preparation Kit