Spermatogenic cells were isolated from P12 and P18 testes which were digested with collagnease and trypsin followed by filteration through a 40 micron sieve. Cells were prepared for ATAC-seq as described (Buenrostro et al 2013) ATAC-seq libraries were created using protocol from Buenrostro et al 2013, and processed using Nextera adapter sequences for Illumina sequencing