Mutations in the Crumbs homolog 2 (CRB2) gene cause various autosomal recessive genetic diseases, such as leber congenital amaurosis, retinitis pigmentosa and ventriculomegaly with cystic kidney disease. However, the precise roles of CRB2 in cell fate determination remains unknown. Here, we generated a homozygous CRB2 knockout (CRB2