Spatiotemporal Expression Pattern of Gadd45g Signaling Pathway Components in the Mouse Uterus Following Hormonal Steroid Treatments

The uterus is a hormone-dependent organ under the control of estrogens, progestins and androgens. The actions of estradiol (E2) and progesterone on uterine physiology are well documented, while active androgens such as testosterone and dihydrotestosterone (DHT) are now also recognized to exert an important role to appropriately maintain the cyclical changes of the endometrium. Based on our previous observations that DHT modulates GADD45g and the expression of specific cell cycle genes, the aim of this study was to identify the specific uterine cell types in which these cell cycle genes are modulated by hormonal steroids. Using in situ hybridization and quantitative RT-PCR (QRT-PCR), the localization and measurement of mRNA expression of key cell cycle genes responding to E2 and DHT were performed in the uterus of ovariectomized mice. Interestingly, in situ hybridization experiments demonstrate that Gadd45g mRNA is detected early and strongly in stromal cells only, indicating that the early cell cycle arrest induced by DHT and E2 in the mouse uterus occurs in this compartment. On the other hand, the cell cycle stimulation represented by the late increase of Ccnb1, Cdc2a and Cdc25c gene expression is located exclusively in the glandular and luminal epithelial cells. QRT-PCR experiments confirm the regulation of mRNA expression observed following in situ hybridization. Surprisingly, both hormones appear to trigger effects in the same direction on cell cycle progression, with androgens inducing a lower modulation of gene expression levels. Additional experiments using the human uterine Ishikawa cell line confirmed the implication of the estrogen receptor in the GADD45g up-regulation following treatment with E2 while the regulation triggered by DHT is less clear. These observations illustrate clearly the stroma-epithelium interactions, which finely regulate the uterine physiology via paracrine mechanisms. Additional investigations are definitely needed to determine the exact role played by androgens in mouse uterine growth and differentiation.