library_construction_protocol: Single cell multiome ATAC-seq/RNA-seq was performed using a modified 10X protocol (10X Genomics, protocol CG000169 Rev D). Wild type mouse embryos were harvested at embryonic day E11.5. A single hindlimb bud was dissected in ice-cold PBS and incubated with collagenase II (Gibco, #17101015, 0.2 uL at 100 u/ul) for 10 min at 37 C. Every five minutes, hindlimb tissue was triturated using a P200 pipette for mechanical dissociation into single cells. Immediately after collagenase treatment, 10% FBS (450 uL) was added and dissociated cells were spun down. Supernatant was removed and cells were resuspended in 100 uL of ice-cold 10X nuclear lysis buffer (10X Genomics, protocol CG000169 Rev D) and incubated for 5 min on ice. Ice-cold wash buffer was then added and lysed cells were centrifuged and supernatant removed. Nuclei were resuspended in ice-cold wash buffer, quantified, and inspected for viability using Trypan Blue assay (Bio-Rad, 1450013). 10X Chromium Single Cell Multiome ATAC + Gene Expression kit (10X Genomics, 1000285)