Detection of multiple bone morphogenetic protein messenger ribonucleic acids and their signal transducer, Smad1, during mouse decidualization

Decidualization is a process characterized by morphological and functional changes in the uterine stromal cells. In addition to steroid hormones, grow th factors are implicated in this process. Using in situ hybridization, we found that mRNAs for several bone morphogenetic proteins (BMPs) were detect ed in the decidual and vascular endothelial cells. The Bmp7 mRNA was detect ed in the decidualizing stromal cells surrounding the blastocyst and distri buted in a gradient, with the highest levels occurring near the uterine epi thelium at 4.5 days post-coitus (dpc). With the progression of decidualizat ion, Bmp7 signals in the deciduum at the antimesometrial side decreased, bu t strong signals were retained in the decidual area at the mesometrial side at 7.0 dpc. In contrast, Bmp8a transcripts increased from 5.5 to 7.0 dpc i n the decidual tissue, with the highest levels occurring in the secondary d ecidual zone at the antimesometrial side. The Bmp2, Bmp4 and Smad1 transcri pts were found in the secondary decidual zone, especially at the mesometria l side. The Bmp2 signals were primarily detected in decidual cells, whereas Bmp4 and Smad1 transcripts were mainly detected in vascular endothelial ce lls, suggesting that they may be involved in decidual angiogenesis.