Expression of Smad2 and Smad4 in mouse uterus during the oestrous cycle and early pregnancy

SMAD2 and SMAD4 are intracellular transducers of TGF-beta superfamily. In situ hybridization and semi-quantitative RT-PCR were employed to determine the temporal and spatial expression of Smad2 and Smad4 mRNA in mouse uterus during the oestrous cycle and early pregnancy. Smad2 mRNA was predominantly present in the luminal and glandular epithelium at dioestrus and prooestrus, while Smad4 expression was at a steady level in the luminal and glandular epithelium throughout the oestrous cycle. During pre-implantation period, Smad2 hybridization signals were accumulated in the luminal and glandular epithelium at a basal level; Smad4 mRNA appeared in the epithelium with a little variation in hybridization signal intensity. After implantation, on day 5 of pregnancy, Smad2 signals were localized to the subluminal stroma surrounding the implanting blastocyst, and Smad4 mRNA were accumulated in the decidua near the luminal epithelium. Both Smads were present in the decidua on days 6-7 with a switch from the mesometrial pole to the antimesometrial pole. RT-PCR results showed that both Smad2 and Smad4 mRNA levels were rising during peri-implantatation. The results suggest that Smad2 and Smad4 might be involved in the cycling changes of mouse uterus during the oestrous cycle and embryo implantation.