Female mice used were SvJ/129, 10-16 weeks of age, with both copies of the Hoxa-10 gene (GenBank # NM_008263) disrupted. These mice were littermates of Hoxa-10+/+ mice used in parallel experiments. 14 days after ovariectomy, mice were injected subcutaneously with progesterone dissolved in sesame oil (Sigma; 0.2mg/0.1mL/mouse), followed by sacrifice and removal of uterine horns at 6 hours after injection. 8 uterine horns from 4 mice were pooled to form one sample. Total RNA preparation, cRNA labeling and hybridization were performed according to recommendations by Affymetrix.