Homozygous lethal. Homozygous embryos have defects in the heart, visceral muscles and nervous system. Interruptions are seen in the dorsal vessel. Cardial cells are present and migrate properly to a dorsal position, but in some places they are not arranged as a continuous layer but appear as unorganised clusters of cells. The same types of defects are seen in the visceral mesoderm. Longitudinal axons are often missing in the nervous system, and important modifications are seen in the guidance and axonal growth of motoneurons. Heart epithelial cells remain round and do not show signs of shape remodelling. Pericardial cells are absent from their normal location of being attached to the basal membrane of the cardioblasts.