Steroid hormones, estrogen, and progesterone, promote extensive cell proliferation, differentiation, and remodeling in all compartments of the uterus during pregnancy (1 -5 ). These hormones orchestrate the entry of the fertilized ova into the uterus, prepare the uterus for embryo implantation, and maintain an environment conducive to the growth and development of the implanted embryo. The cellular actions of these hormones are mediated through specific intracellular receptors. These receptors function as ligand-inducible transcription factors (6 -8 ). It is generally believed that the cellular events leading to the establishment and maintenance of pregnancy are mediated through the expression of specific steroid-regulated genes in the uterus. The identification of these steroid-regulated genes is crucial for understanding the molecular and cellular processes that control uterine growth and differentiation during pregnancy.
