A transgene-induced mitotic arrest mutation in the mouse allelic with Oligosyndactylism.

Oligosyndactylism (Os) is a radiation-induced mutation on mouse chromosome 8 associated with early postimplantation lethality in homozygotes and abnormal development of the limbs and kidneys in heterozygotes. The recessive lethal effect of Os is due to a mitotic block of the embryonic cells that becomes apparent at the blastocyst stage, but it is not known if the heterozygous effect of Os is due to haploinsufficiency of the gene responsible for the mitotic arrest, or is due to mutation(s) of other gene(s). We have recently described a transgene-induced recessive mutation, 94-A/K, that results in early postimplantation death of the embryos, and we have mapped this mutation to the same region of chromosome 8 where Os has been assigned. On the basis of complementation tests between transgenic and Os/+ mice, in vitro growth characteristics and increased mitotic index of 94-A/K embryos, and molecular structural analysis of 94-A and 94-K transgenic and Os/+ mice, we conclude that the 94-A/K mutation represents a new allele of Os. This insertional mutation should facilitate the isolation of a mammalian gene essential for normal progression of the cell cycle beyond metaphase.