Studies on "repeated epilation" mouse mutant embryos: I. Development of facial malformations.

Repeated Epilation Er/Er mouse embryos show severe facial malformations. The most obvious is an important decrease in prominence of facial features. The protuberance of the snout is reduced. The eyes, the mouth, the nares and the ears are modified. From 13.5 days onwards the lips begin to close, the joining proceeding from the lateral to the central part. The nares, eyelids, oral opening, and auditory ducts are in the course of closure from 14 days of pregnancy. This process is terminated at 15 days. At the microscopic level, disturbances begin to appear at 13 days. They are limited to the anterior part of the face. During the next few hours, they become more important. At 14 days, the maxillae are joined from the anterior extremity of the snout. The oral opening is thus closed. Then, an oral cavity of very reduced form and dimensions is formed. The tongue connects the nasal septum to the mandible. A general process of closure occurs between: nasal septum, maxillae, tongue, and palatal shelves. Extensive modifications result from the compression of all these areas, especially of the tongue and shelves which remain in vertical position. An atypical cleft palate is seen, due to the absence of shelf movement, impeded by the tongue and the joinings mentioned earlier. The compression increases at 15 and 16 days. However, complete epithelial fusions do not occur. In 18-day-old embryos, cystic malformations appear in the glosso muscular system.