Cell migration in the ruminant placenta: a freeze-fracture study.

In the ruminant placenta, binucleate cells normally migrate out of the trophectodermal epithelium throughout pregnancy to fuse with the syncytium bounding the maternal connective tissue. This study shows that they form part of the trophectodermal tight junction as they migrate, thus maintaining the barrier function while penetrating the junction. This method of migration seems to be unique and the means by which it is achieved is briefly discussed.