Gene expression of transforming growth factor-β receptors types I and II in rat endometrium during the estrous cycle and early pregnancy

Roles of transforming growth factor-β (TGF-β) receptor types I (TβRI) and II (TβRII) during the estrous cycle and implantation of rodents are currently unclear. In the present study, the spatial and temporal expressions of TβRI and TβRII in rat endometrium during the estrous cycle, pre-, and peri-implantation were examined using in situ hybridization and semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). With in situ hybridization, TβRI and TβRII were expressed at weak levels in rat endometrium during the estrous cycle. During pre-implantation, both receptors were expressed in the luminal epithelium and glandular epithelium on Days 0.5 and 1.5 of pregnancy, but were down-regulated on Days 2.5 and 3.5. During peri-implantation, both TGF-β receptors were localized in the luminal epithelium and subepithelial stroma to facilitate attachment reaction and trophoblast invasion. They were highly expressed on Day 4.5, whereas were down-regulated on Days 5.5 and 6.5. Semi-quantitative RT-PCR analysis confirmed the data obtained by in situ hybridization. These results suggest that during pre-implantation, both TGF-β receptors are functional in the proliferation of endometrial epithelial cells. During peri-implantation, both TGF-β receptors play important roles during the onset of the uterine receptivity and the attachment reaction. TGF-β signaling is down-regulated when trophoblast invasion begins.