The initiation and control of trophoblastic growth in the mouse: binucleation and polyploidy.

Initially diploid, pure trophectodermal derivatives were dissociated and grown in culture. Over the 72-hour time course in vitro, uninucleate, binucleate and a small number of multinucleate cells appeared. Moreover, the pattern of binucleation found in these trophoblast cultures resembled that seen during the development of the mouse liver. Thus, the binucleates displayed a progressive increase in nuclear DNA content and the increased DNA values ranged from 2c to 32c. Furthermore, the proportion of uninucleate and binucleate cells changed systematically with growth in vitro and the final binucleate cell population became, on average, 10 to 15 per cent of the total. These results, together with those of other studies, suggest that mouse trophoblast can initially become giant through a binucleate phase.