Mice that are heterozygous for the targeted mutation are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities. Homozygous mice have an embryonic lethal phenotype, failing to develop past 11.5 days post coitum (d.p.c.). Placental formation is defective due to the failure of the chorion and the allantois to fuse. Morphological disorganization of the chorion is observed by 8.0-8.25 d.p.c. Integrin alpha 4 protein is not detectable in homozygous mutant chorionic cells by immunohistochemical analysis. This mutant mouse strain may be useful in studies related to the failure of chorion and allantois fusion during placental development. The Jackson Laboratory 2024, used with permission.