AN EMBRYOLOGICAL STUDY OF MOUSE EAR USING THE WHOLE EMBRYO CULTURE TECHNIQUE

Abstract

Mouse embryos were explanted at 11.5 days of gestation and cultured for periods of 6, 12, 18, 24, 30, 36, 42 and 48 hours using the whole embryo culture system. A continuous flow of gas (5%CO₂+95%O₂) was maintained through the culture bottles during the culture periods. The cultured embryos were morphologically and histologically examined at the end of the designated periods. The growth of the embryos was depressed after about 36 hours, and differentiation was retarded as the culture time increased. General development had ceased almost completely by 42-48 hours. At 18-36 hours, the external auditory canal and pinna, which are not developed in 11.5 day embryos, could be observed clearly on the surface of the head. After 42 hours, the facial features including the external ear were similar to those of 13 day in vivo embryos. Serial sections of the ear region of cultured embryos showed that development of the inner and middle ear structures up to 42 hours was the same as that seen from 11.5 to 13 days in vivo. In the inner ear, the otocyst had developed into the vestibule, cochlea and semicircular canals by 12-30 hours. In the middle ear, the stapedial anlage appeared and its circular shape became clear between 0 and 12 hours. Subsequently, the medial portion of the stapedial anlage grew until it was abjacent to the developing otic capsule, and the anlages of other ossicles were also recognizable after 18 hours. Differentiation of the horizontal portion of the facial nerve was noted at the same time that the stapedial anlage and otic capsule were developing. In conclusion, this morphological and histological study has clearly demonstrated that early organogenesis of the ear (especially the middle ear), corresponding to days 11.5-13 of in vivo development, is reproducible in a whole embryo culture system.