THE EMBRYONIC-DEVELOPMENT OF SENSORY ORGANS AND THE SKULL IN THE TRISOMY-16 MOUSE, AN ANIMAL-MODEL FOR DOWNS-SYNDROME

The trisomy 16 mouse is a widely accepted animal model for the study o f the embryonic development of human trisomy 21. While the development of the brain and heart has been thoroughly studied, there are hardly any data on the development of sensory organs like the eye, nose and e ar. By studying scanning electron microscopic pictures and semithin se ctions from the tenth to the 15th day of development, we found delayed development of the nose, and, in particular, of the vomer. Sensory st ructures of the otic vesicle also showed a marked developmental delay. Pigmentation of the outer layer of the otic cup starts later in triso mic animals. Cleared specimens on day 16 showed retarded development o f ossification centres in all areas of the skull. These findings corre spond with the abnormal facial morphology found in Down's syndrome and may also provide new insights into the hearing impairment commonly fo und. The observations in the eye and skull bones indicate that neural crest tissue maldevelopment is not the sole cause of malformations.