The expression of nuclear retinoid receptors in human implantation

Vitamin A and retinoids play an important role during development. They aff ect morphogenesis, cell growth and differentiation by interacting with two types of receptor, the RARs and the RXRs. Despite the well known establishe d teratogenic effects of retinoids during human pregnancy, little is known about the effect of retinoids on human placental development. We studied the possible involvement of retinoids during the implantation pr ocess by investigating the spatial distribution of retinoid receptors in th e human implantation site by in situ hybridization and immunohistochemistry . For in situ hybridization, we used digoxigenin-labelled antisense ribopro bes. Immunochemical staining was performed with specific antibodies against the various retinoid receptors and a streptavidin-alkaline phosphatase imm unostaining kit. We found that only two types of receptors were expressed at the implantatio n site: RAR alpha and RXR alpha. Both types of receptors were present in th e proliferative intermediate trophoblast, the invasive extravillous trophob last and decidual cells. Both receptors were also present in the villous cy totrophoblasts. The presence of this retinoid receptor in the cytotrophobla sts suggests a key role for all-trans retinoic acid and/or 9-cis retinoic a cid in the development of human placenta. (C) 2000 Harcourt Publishers Ltd.