In vivo and in vitro studies on the early embryonic lethal oligosyndactylism (Os) in the mouse.

The development of mouse embryos homozygous for oligosyndactylism (Os) is arrested during implantation. Histological investigations confirm a previous report that cells become blocked in mitosis, and air-dried spreads of the mutant embryos reveal that large numbers of cells accumulate in metaphase. Trophoblastic giant cells appear unaffected by the action of the mutant gene both in utero and during culture over the lethal phase. It is proposed that the form of endoreduplication undergone by giant cells renders them refractory to the metaphase block.