Early development of the otocyst in an exencephalic mutant of the mouse.

Development of the otic anlage was studied by means of scanning electron microscopy in exencephalic loop-tail (Lp/Lp) embryos and in their normal (+/+; Lp/+) littermates at 8.5-9.5 days of gestation. In the abnormal embryos, the cells of the otic pit lack the rounded prominent surfaces and dense arrangement of microvilli which characterize the normal otic pit, and the overall configuration of the otic anlage is also distorted. The relatively early manifestation of abnormalities in the otic anlage of this mutant suggests that the defective neural tube may exert an influence as early as the otic placode stage, or that a common factor may simultaneously affect both otic and neural tube development in this mutant.