Influence of the Neural Tube on the Differentiation of the Inner Ear in the Mammalian Embryo

Abstract

IT has long been known from transplantation experiments that in amphibians and birds the differentiation of the otic vesicle into a normal labyrinth depends on the influence of the neural tube^1–4, but on account of the technical difficulties involved it has not been possible to extend these findings to mammals by means of similar experiments. The use of mutant mice is the most promising way of circumventing these difficulties. An analysis of the abnormalities of the inner ear in kreisler (kr/kr) mice⁵ provided evidence that the neural tube plays the same part in the differentiation of the inner ear in mammals as in amphibians and birds. Confirmatory evidence was obtained from a study of dreher (dr/dr) mice⁶. It had been known for some time that, in this mutant, the differentiation of the inner ear was faulty. It was argued that, if the kreisler interpretation was correct, then in dreher embryos abnormalities of the neural tube in the region of the myelencephalon might precede those of the inner ear. This turned out to be the case⁶. Still further confirmatory evidence can be obtained by approaching the problems from the opposite direction, that is, by examining the inner ear in mutants where nothing is known about this organ but where the neural tube is known to be abnormal. Such an attempt is the subject of this report.