The development of field vole (Microtus agrestis) and mouse blastocysts in vitro: a study of trophoblast cell migration.

Outgrowth of field vole blastocysts and their constituent tissues in vitro results in the appearance of trophoblast giant cell monolayers plus migratory cells of two types. The large migratory cells, which are never seen in mouse outgrowths, resemble trophoblast giant cells in morphology and DNA content. They probably correspond to giant cells which have been observed to migrate throughout the endometrium of vole implantation sites in vivo. It is suggested that their appearance in vitro may depend upon an interaction between the trophectoderm and inner cell mass (ICM) of the blastocyst. Small migratory cells also emerge from vole explants and are occasionally seen in mouse outgrowths. They are probably of ICM origin, and in some cases have given rise to long-term vole cell lines.