Scientists have identified a key gene involved in embryo implantation in mice. The gene makes a uterine protein known as C/EBPb, which is regulated by oestrogen and progesterone. The researchers say the protein must be present for pregnancy to occur in mice. The team, from the University of Illinois, created a mouse model lacking C/EBPb and used it to observe the relationship between hormones and receptors around the time of implantation. They found that the protein is critical to the way the uterus responds to steroid hormones. The paper is reported in the Proceedings of the National Academy of Sciences.
C/EBPb is normally produced rapidly and in large quantities during the critical four day implantation period in mice that follows ovulation. During this period the embryo attaches to the uterine wall and eventually attaches, through the placenta, to the maternal blood supply. In order for this connection to occur, a critical change in the uterine tissue known as decidualisation must take place, which allows the embryo to link to the mother's blood supply. Lead researcher Professor Milan K. Bagchi said, 'We have demonstrated very clearly in the mouse that in the absence of C/EBPb there is no decidualisation. We transferred viable mouse embryos from healthy mice into mice lacking the gene, and pregnancy failed'.
Co-author of the study Indrani C. Bagchi, Professor of Veterinary Biosciences in the College of Veterinary Medicine at Illinois, believes the finding could contribute to more successful infertility treatment. 'The success rate for the practice of IVF currently is, on average, about 25 per cent. The major problem is that the conditions occurring when the embryo is transferred often are not the best in the uterus. It's not known if the uterus is ready to accept an embryo, so often multiple embryos are transferred in hopes that one will attach. In future studies, confirmation of C/EBPb as a marker that correctly indicates uterine readiness for implantation in the human is likely to alleviate these shortcomings'. The protein is known to occur in humans but more research is necessary to establish whether it has the same function. If the findings are replicated in humans the protein's presence could become a vital gene marker for predicting uterine readiness for pregnancy.
Richard J. Paulson, Professor of Reproductive Medicine at the University of Southern California, responded to the report by pointing out that doctors already have effective methods of helping patients overcome implantation difficulties and that the research is 'far away from the human'. He added that, 'In women who have had their ovaries removed, giving them estrogen and progesterone can induce pregnancy that is just as good as it is in women who have functioning ovaries'. He also noted that, as yet, there was no identification of a population of women that do not respond to these hormones but that the study does add to our overall understanding of key factors in pregnancy.