The cytoplasmic expression of E-cadherin and β-catenin in bovine trophoblasts during binucleate cell differentiation

Binucleate cells are endocrine cells generated by the acytokinesis and endoreduplication of the trophectoderm in the ruminant placenta. These cells are migratory and secrete hormones into the maternal circulation after fusing with uterine epithelial cells. In this study, we performed immunohistochemistry for E-cadherin and β-catenin in bovine placenta and a bovine trophoblast cell line (BT-1). We found that E-cadherin and β-catenin were distributed not only at the cell to cell boundary but throughout the cytoplasm in binucleate cells, although they were concentrated at the cell to cell boundary in epithelial cells in bovine placenta. Moreover, β-catenin was detected in the nuclei of binucleate cells. Binucleate cells after fusion with uterine epithelial cells (feto-maternal hybrid cells) in the maternal side showed no intracellular expression of E-cadherin and β-catenin. The transformation into binucleate cells in the BT-1 cell line was also accompanied by the cytoplasmic accumulation of E-cadherin and β-catenin. We further demonstrated that levels of cytoplasmic β-catenin were well correlated with the DNA content of binucleate cells in BT-1. The dynamic changes in the distribution of E-cadherin and β-catenin suggest an important role in binucleate cells, including the rearrangement of cadherin-mediated cell adhesions during cell migration and the onset of endoreduplication probably via the nuclear transfer of β-catenin.