115 RAT EPIDERMAL GROWTH FACTOR GENE EXPRESSION CONTROLLED BY PROGESTERONE DURING PREGNANCY

Abstract

The implantation of the developing blastocyst into the uterine wall is regulated by a precisely timed interplay of the ovarian hormones estrogen and progesterone, which control a set of regulatory factors that make the uterus receptive to implantation. These factors include EGF receptor (Egfr) and members of the epidermal growth factor (Egf) family, namely, EGF, heparin-binding EGF (Hbegf), transforming growth factor-alpha (Tgfa), and amphiregulin (Areg). However, the exact role(s) these factors play in pregnancy remain unclear. To address this, a group of three rats was euthanized every day from gestation day (GD) 0 through to GD21. The uterus, attached uterus (these tissues are mostly composed of stromal cells), and placenta were rapidly excised and used directly for total RNA. We used real-time PCR with the TaqMan system (Applied Biosystems, Foster City, CA, ISA) to examine the uterine expression patterns of these factors in rats during the entire pregnancy. Data were analyzed by nonparametric one-way analysis of variance using the Kruskal-Wallis test, followed by Dunnett's test for multiple comparisons. Egf and Egfr mRNA levels increased significantly at implantation, especially on GD3 and GD6, after which their expression gradually decreased. Hbegf and Tgfa showed a modest spike of transcription around the implantation period (GD4 and GD3, respectively) but were much more strongly expressed at mid-pregnancy, which is when progesterone is secreted at high levels. Areg expression peaked strongly around implantation (GD4) and at mid-pregnancy (GD12). Treatment of pregnant rats on GD5 or GD8 with the progesterone receptor antagonist RU486 (2.5 mg per rat) blocked the expression of all of the genes on the days of treatment. Moreover, injection of immature rats with progesterone induced the uterine expression of all of the genes except Hbegf, while injection with estrogen or estrogen plus progesterone had no effect. Taken together, all genes tested may be assumed to regulate the implantation process. Moreover, Hbegf, Tgfa, and Areg may participate during mid-pregnancy. In addition, all of these activities are likely to be controlled by progesterone in the uterus of rats during pregnancy.