Analysis of Palatogenesis in the Mouse with Exencephaly Induced by Cadmium Chloride

Abstract

ABSTRACT It has been revealed that exencephalic mouse embryos were resistant to cleft palate induction when they were exposed to several teratogens known as cleft palate inducing agents. In the present study, palatogenesis in exencephalic mouse embryos, which were not exposed to cleft palate inducing teratogens, was observed. A single dose of 6 mg CdCl2/kg body weight was intraperitoneally injected into pregnant Jcl:ICR mice at day 7.5 of gestation (plug day = day 0). Embryos were dissected from uterus at day 13.5 to 15.5, and the secondary palate was observed with a dissecting microscope or a scanning electron microscope (SEM). Of live embryos, 71.5% had exencephaly. Palatal shelves of exencephalic embryos were elevated earlier than non‐exencephalic embryos, and there seem to be two modes of palatal fusion in exencephalic embryos. (1) “Parallel‐shape.” The anterior part of shelves were elevated at day 13.5. Distance between the opposite medial edges of both shelves decreased at the posterior part, and this closing proceeded to the anterior part, where the shelves began to fuse. (2) “V‐shape.” The posterior part of palatal shelves became closer at day 14.0 or day 14.25. The medial edge of both shelves began to fuse at this part, and this fusion proceeded anteriorly. The anterior parts of the shelves were elevated, and the medial edge of the anterior shelves was fused independently. It is suggested that these alterations of palatogenesis in exencephalic embryos are related to inhibitive mechanism(s) against cleft palate induction. Key words: palate, neural tube defects, skull, mice, cadmium