Mammary tissues from specific stages during pregnancy and lactation were harvested, and stored at -80°C. The frozen-stored tissues were ground into powder in liquid nitrogen. Chromatin was fixed with formaldehyde (1% final concentration) for 15 min at room temperature, and then quenched with glycine (0.125 M final concentration). Samples were processed as previously described. The following antibodies were used for ChIP-seq: STAT5A (Santa Cruz Biotechnology, sc-1081), GR (Thermo Fisher Scientific, PA1-511A), H3K27ac (Abcam, ab4729), H3K4me3 (Millipore, 17-614), NFIB (Santa Cruz Biotechnology, sc-5567), and RNA polymerase II (Abcam, ab5408). Libraries for next-generation sequencing were prepared and sequenced with a HiSeq 2500 instrument (Illumina). Libraries for sequencing were prepared using standard Illumina protocols.