Mice that are homozygous for this mutation survive to term or die very shortly after birth. The gene trap insertion appears to have occurred between the translational start sites of the long and short forms in the 5' portion of the endogenous gene. No gene product (protein or mRNA) is detected in homozygous embryos. Mutant embryos can be distinguished by E9.25 as the lateral edges of the cranial neural folds exhibit a wavy appearance and fail to converge at the dorsal midline. As the embryo develops, the neural folds continue to enlarge and develop away from the dorsal midline, presenting a mushroom-like appearance. By day E14.5, failed neural tube closure results in exencephaly, acrania, and facial clefting. Some mutants exhibit defects in ventral closure resulting in herniation of the intestine and liver. Not all aspects of the phenotype are fully penetrant. Hemizygous mice express a B-galactosidase under the control of the endogenous promoter, with expression variously observed in the neural tube, forebrain, somites, ventral body wall, heart, gut and skeletal muscle.
