Abstract
In laboratory mice, cleft lip, cleft lip with palate and cleft palate are generally very rare. However, the cleft lip with or without cleft palate occurred spontaneously at higher frequencies in one family of inbred mouse “A” strains. In addition, it has been known that cleft palate can be induced in fetal mice by injection of cortisone during a sensitive period of gestation. Recently, the “A” strains of mice have been utilized extensively as models to study the genetic factors and the processes involved in clefting of the lip and palate. Of the “A” substrains, the A/WySn mouse was utilized in this study to investigate the frequency of spontaneous cleft lip with or without cleft palate and cleft palate, and detect their susceptibility to this teratogenic effect that cortisone-induced orofacial clefts. Another was used to compare the differences in incidence between the A/WySn and C 3 H/He strains. Pregnant mice were injected on days 11 through 14 of gestation with 100 mg of cortisone per kg of body weight. As a control group the pregnant mice were not treated with the drugs mentioned above. The frequency of each cleft was observed among embryos that attained at least Day 18 of development. In the control group, A/WySn was found to have a frequency of spontaneous cleft lip and cleft lip with palate being 3.7% (9/241) and 10.8% (26/241), respectively, but cleft was not found in C 3 H/He strains. Further, the incidence of cortisone-induced cleft palate in A/WySn for 40.6% (65/160) was significantly higher than 16.7% (8/48) in C 3 H/He. The mean living fetuses showed significant decreases in the A/WySn, showing no appreciable decreases in C 3 H/He when the pregnant mice were treated with cortisone, indicating the susceptibility to the teratogenic effect of cortisone in A/WySn. The significantly different frequency occurring the orofacial clefts between A/WySn and C 3 H/He suggested however that this may apply to genetic research for human congenital cleft lip, cleft lip with palate and cleft palate as the animal model thought genetic crosses between the two strains of mice.
