To examine the effects of hormone stimulation on Esr1-wildtype and Esr1-mutant mammary glands, we will ovariectomize both wildtype and ER-mutant mice. Following ovariectomy (OVX), animals will be implanted with hormone pellets (either placebo, estrogen, and/or progesterone). Then, we perform RNA-seq on FACS-sorted mature luminal cells (ML) from mammary glands of treated mice. This analysis will allow for separation of ER mutant-intrinsic effects on gene expression vs. combinatorial effects from exposure to either estrogen or progesterone.  Overall design: 37 samples are included, 3 biological replicates per condition (except for the 'WT + P4' condition, which has 4 biological replicates). 'WT + placebo' condition is used as a reference.