Islets were washed twice with ice cold 1xPBS by spinning at 500g for 5mins at 4°C. Cell lysis was performed with ATAC lysis buffer (10mM Tris-HCl, pH 7.4, 3mM MgCl2, 10mM NaCl and 0.1% IGEPAL CA-630) by incubating on ice for 10mins and nuclei were then collected by spinning at 500g for 10mins at 4°C. The transposition reaction mix (12.5μl of 2X TD buffer, 2μl of Tn5 transposase (Illumina, San Diego, CA, USA) and 10.5μl of nuclease free water was added to nuclei and incubated at 37°C for 1hour before the reaction was cleaned using MinElute cleanup kit (Qiagen, Hilden, Germany). Next, 10-12cycles of PCR were performed with transposed DNA using the Illumina Nextera dual index primers. The PCR product was cleaned using PCR purification kit (Qiagen).