FIG. 2.

Hypomorphism of the yy1^flox allele. (A) Weight of the conditional knockout mice. Heterozygous yy1^flox/+ mice were intercrossed, and the weight of their offspring was determined 3 to 6 weeks after birth. The weight of mice heterozygous for the constitutive yy1 knockout allele (yy1^+/−) generated from independent crosses is shown as a comparison. Within each litter, the weight of the mutant (yy1^flox/+, yy1^flox/flox, and yy1^+/−) mice was expressed as the percentage of the average weight of their wild-type (yy1^+/+) littermates of the same sex. Each bar corresponds to the mean ± standard deviation of n mice, with values obtained from several (>5) independent crosses. *, P < 0.001, yy1^flox/flox and yy1^+/− versus yy1^+/+ littermates (Student's t test). (B) YY1 expression in the yy1^flox/flox conditional knockout mice. Western blot analysis of YY1 expression level in various organs harvested from 3-week-old homozygous yy1^flox/flox mice and their wild-type (yy1^+/+) littermates. YY1 was detected with an anti-YY1 (H414) antibody, and an antiactin (MAB1501) antibody was used to verify equal loading of the protein extracts. Densitometry analysis revealed that the YY1 protein level in the liver, lung, kidney, and thymus of the yy1^flox/flox mice corresponded to 52%, 46%, 54%, and 46%, respectively, of that detected in tissues isolated from their wild-type littermates.