Homozygous null mice have a perinatal lethal phenotype and do not survive long after birth due to respiratory failure. Mice that are heterozygous for the targeted mutation are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities. No gene product (protein) is detected by immunohistochemical analysis in homozygotes. Homozygous 17.5 to 18.5 embryonic day old embryos exhibit severe shortening in all outgrowing axes of the body and limbs with loss of distal structures (absence of tail, limb digits and genital tubercle), and truncated facial features. Newborn homozygous mice succumb to asphyxia due to abnormal lung development and display shortened trachea, overexpansion of the distal airways and impaired capillary/alveolar coupling. This mutant mouse strain may be useful in studies of distal outgrowth of internal organs and organization of morphogenesis in development. The Jackson Laboratory 2024, used with permission.