Article révisé par les pairs
Résumé : Morphological and histochemical aspects of the early development of inner ear and adjacent ganglia have been studied in abnormal mouse embryos bearing gene Dc (Dancer) and collected at the 9- to the 12-day stages. Abnormalities have been found in embryos of all stages studied. Abnormal Dancer embryos (Dc/Dc and Dc/+) show a delay in neural tube closure and in cephalic neural crest migration. The developing otic region shows bilateral asymmetries. Otocyst and ganglionic defects show considerable variations, even between both sides of the same animal. Dancer embryos also exhibit a general delay in body growth and other cephalic anomalies. The invaginating otic placode does not make contact with the rhombencephalic neural wall. This defect is accompanied by a delay in otic vesicle closure and in presumptive ganglionic cells migration from the primary auditory epithelium. A delayed modelling characterizes the anterior region of the otocyst. The main structures affected are the superior and lateral semicircular ducts and the utriculus. Sensory areas of the superior and lateral ampullae and of the utricular macula show a defectuous differentiation or are missing. The posterior region of the otocyst develops normally. The lateral portion of the stato-acoustic ganglion primordium is smaller in Dancer embryos. Abnormalities also appear later on in the ganglionic lateral arm of the medial portion. The branches of the developing superior vestibular nerve may be thinner, aberrant or absent. The utricular branch is always missing. The fibers of the future inferior vestibular nerve are not affected. Certain central nerve connections are reduced or absent, or their formation is delayed in Dancer embryos. These connections are the facial motor roots and the sensitive roots of the developing superior vestibular ganglion.