Multinucleate cells in cultures of human amniotic fluid form by fusion

The major class of cells subcultured from human amniotic fluid retains properties of trophoblast. The objective of this study was to determine whether the multinucleate cells appearing in these cultures form by fusion, as is true for syncytiotrophoblast. Culture methodology involved subdivision of one flask into two, one of which was labeled with 3H-thymidine and the other with 14C-thymidine. Aliquots of each labeled culture were mixed together and allowed to grow. Autoradiographic study revealed binucleate cells containing one nucleus labeled with 3H and the other with 14C. This result indicates that fusion is one means by which binucleate cells form. The distribution of labeled and unlabeled nuclei in 217 binucleate cells obtained in two experiments was then determined. The distribution conformed to that predicted from the assumption that fusion was random and the only way for binucleate cells to form. We conclude that the binucleate cells appearing in cultures of human amniotic fluid form by fusion, as do the multinucleate cells in trophoblast. Our results suggest further that fusion is the sole means by which binucleate cells arise.