Matings for timed embryo isolation were set up using standard animal husbandry techniques. Noon on the day of vaginal plug observation was considered embryonic day (E) 0.5. Embryos were isolated at E8.5- E10.5. Embryo tailbuds were dissected just prior to the terminal somite, snap frozen in liquid nitrogen and stored at -80 C. All procedures were done at 4C to minimized degradation of nuclei, and following the previously published protocol (Buenrostro et al) except as noted here. Each tailbud was disrupted in 200 uL of NIB with 0.5% Triton-X buffer by pipetting up and down. Then the samples were spun, supernatant removed and was followed by a second wash with RSB buffer. Each pellet of nuclei was then transported using a home-made Tn5 enzyme (Scott et al 2016; +GR ref). After 30 minutes of incubation at 37C, each sample was cleaned up with MinElute PCR purification kit (Qiagen)