title: ATACseq-Mat_R2
design: The ATAC-seq library was prepared based on the OMNI-ATAC seq method with modifications as described below. Mature upper arm and upper arm blastemas (7.5 to 8cm animals) from 13 days were isolated by cell sorting from the converted Prrx1:Cre-ER;CAGGs:lp-Cherry transgenic strain.  Embryonic ATAC-seq was prepared from cells isolated from d/d strain embryos. Stage 40 early embryonic limb bud cells were prepared from 10 whole limb buds. ATAC-seq libraries were performed from 1.5 to 2 x104 K cells. After cell isolation, the isolated fibroblast cell suspensions were spun down (250 x g for 10 min at 4) and re-suspend in 500 l lysis buffer No.1, mix gently and spun down (250 x g for 10 min at 4). The pellets were resuspended in 100 l Lysis buffer No.2 and incubated on ice for 10 min. Lysis buffer No.3 was added to the cells and mixed gently. Immediately, cells were spun down (250 x g for 10 min at 4) and pellets were resuspend with 50 l  Tn5 Transposase reaction mixture (Transposase reaction: 5 l of the 5x Transposase buffer (in-home): 50 mM TAPS-NaOH (pH 8.5), 25 mM MgCl2, 50% DMF, 16.5 l of PBS, 1 l of 10% Tween-20 (0.1 % f. c.), 1 l of 1% Digitonin (0.01 % f. c.), 2.5 l of assembled in-home Tn5 (0.5 g of assembled Tn5 was used for a reaction. Tn5 assembly with adapters was carried as follows. Transposition with Tn5 was carried out at 37 for 1 hr with occasional agitation. The reaction was stopped by adding a 5 times volume of PB buffer (QIAGEN) and vortexing for 30 second. Tn5 treated DNA was purified (QIAGEN mini purification kit) and eluted with 20 l of EB buffer. 10 l of purified DNA solution was used for library amplification, and final amplification cycles were defined with intermediate qPCR as described in the original ATAC-seq method 37.  Final libraries were amplified with NEBNext High-Fidelity 2X PCR Master Mix (NEB)). After PCR amplification, the libraries were purified with DNA purification beads.