Vestibular hair cell pathology in the dancer mouse mutant.

The morphogenetic type of inner ear defect in the dancer (Dc/+) mouse mutant affects primarily the vestibular part of the labyrinth. The animals show a circling-waltzing behaviour. The inner ears from 7-day to 12-month-old Dc/+ mutants have been analysed. Apart from gross malformations, the gene caused changes in fine structure which were found primarily in the cuticular plate and the stereocilia. As the cuticle gradually disintegrated, the sensory hairs became disarrayed and later showed hair fusion. The combination of the gross malformations and the specific ultrastructural changes in the hair cells probably interferes with both posture and behaviour and, probably together with a dysfunction of the central nervous system, is the cause of the animal's behaviour.