MGI:1913500Mice homozygous for a knock-out allele reach the egg-cylinder stage but fail to initiate gastrulation and show embryonic growth retardation, a size reduction of the epiblast, extraembryonic ectoderm and pro-amniotic cavity, absence of the primitive node, head folds, allantois, amnion and chorion, and complete embryonic lethality prior to organogenesis.