Detection of class I MHC mRNA in subpopulations of first trimester cytotrophoblast cells by in situ hybridization

Class I MHC mRNA has been identified in both villous and extravillous cytotrophoblast cells in first trimester placentas by in situ hybridization. In this report, we expand those observations to additional morphologically and anatomically distinct subpopulations of trophoblast cells in early placentas using the same experimental approach. In the transition zone of first trimester placental villi, where cytotrophoblast cells are proliferating to form new villi or to migrate into adjacent tissue, both cytotrophoblast cells beneath the uninterrupted syncytium and the proliferating cytotrophoblast cells contained class I mRNA whereas a layer of cytotrophoblast cells proximal to the villus core did not contain class I mRNA. In the placental bed, migrating cytotrophoblast cells contained high levels of class I mRNA as determined by the intensity of staining. In contrast, multinucleated giant trophoblast cells contained little specific message. Alterations in levels of class I mRNA seem therefore to be associated with trophoblast proliferation, migration and differentiation.