Multiparameter in situ analysis of trophoblast cells in mixed cell populations by combined DNA and RNA in situ hybridization.

We developed a non-radioactive assay for simultaneous detection of cytoplasmic mRNA and nuclear genomic DNA in fetal trophoblast cells by sequential in situ hybridization. Trophoblast-specific mRNA is detected with a digoxigenin-labeled RNA probe complementary to HLA-G, followed by visualization through the generation of stable contrast-rich DAB/Ni complexes. Genomic target DNA is subsequently visualized in labeled cells by fluorescent in situ hybridization using biotin-labeled chromosome-specific DNA probes. Simultaneous visualization of both targets is made possible using a fluorescence microscope with FITC filter and conventional brightfield light. This method allows detection of trophoblast cells within a mixed cell population and, at the same time, analysis of chromosome anomalies in the trophoblast cells identified. For prenatal diagnosis of fetal cells enriched from maternal peripheral blood during pregnancy, this multiparameter in situ analysis of immobilized fetal trophoblast cells will be very useful.