GAP JUNCTION AND TISSUE INVASION - A COMPARISON OF TUMORIGENESIS AND PREGNANCY

1. Trophoblast invasion during embryo implantation in some aspects res embles tumour cell invasion but, unlike tumour cells, trophoblast cell s are able to differentiate and establish a placenta, Because direct c ell-cell communication is believed to be involved in growth control an d differentiation, we have investigated connexin (ex) gene expression during trophoblast development, 2. Pre-implantation embryos expressed cx43 as well as cx31 proteins from the 8-cell stage onwards, Following implantation, compartmentalization of both connexins occurred: cx31 e xpression was restricted to the invasive trophoblast cell population, whereas the embryo proper was characterized by cx43. Trophoblast diffe rentiation was indicated by induction of cx26 in the labyrinth and cx4 3 in the spongiotrophoblast accompanied by a disappearance of cx31, Co mparison with trophoblast cell lines revealed that rat trophoblast HRP -1 cells express connexin43, while malignant choriocarcinoma cells exp ress cx31, Treatment with retinoic acid led to a disappearance of cx31 in the choriocarcinoma. Both cell lines reduced their invasion proper ties after retinoic acid treatment, but growth retardation was only ob served in the malignant trophoblast, 3. It seems that the cx31 channel is needed for trophoblast cell populations to maintain the highly pro liferative properties but does not alter their invasion properties.