Allophenic mice in cleft-palate investigations.

T1Wh (Rb (5;19)1Wh), an albino strain of mice not previously used in the investigation of cleft palate (CP), is homozygous for a (5;19) Robertsonian translocation which provides conspicuous chromosomal markers. Preliminary studies in this laboratory revealed that CP is induced in all the offspring of T1Wh females treated with 2.5 mg of cortisone acetate on days 11-14 of pregnancy and that palatal closure is accomplished at a later morphological and chronological age than in C57BL/6J strain mice. The latter strain had a CP frequency of 42% under similar experimental conditions. Eight- to 16-cell embryos were aggregated in the following combinations: T1Wh in equilibrium T1Wh, C57BL/6J in equilibrium C57BL/6J and T1Wh in equilibrium C57BL/6J. The resulting allophenic blastocysts were transferred to pseudopregnant C57BL/6J recipients which were given the above cortisone treatment and killed on the 18th day of pregnancy. CP was found in all of the 48 T1Wh in equilibrium T1Wh fetuses, 4 (20%) of of 20 C57BL/6J in equilibrium C57BL/6J fetuses and in 17 (26.2%) of 65 T1Wh in equilibrium C57BL/6J fetuses. Analysis of chromosome preparations from the palates of the T1Wh in equilibrium C57BL/6J fetuses demonstrated that there is a positive correlation between the presence of CP and the percentage of susceptible cells in the palate (P less than 0.02). Other data suggest a possible growth advantage in favor of C57BL/6J cells in the palates of T1Wh in equilibrium C57BL/6J allophenic mice.