Foxn1 mRNA expression from the Foxn1^lacZ allele is down-regulated after birth. (A) Relative quantity of Foxn1 expression in CD45⁻ total thymic stromal cells (TSCs) of +/+ and lacZ/lacZ mice at newborn stage and at 5 weeks. At newborn stage, Z/Z and +/+ showed similar Foxn1 expression levels in TSCs. At 5 weeks, Foxn1 expression level in lacZ/lacZ thymi was reduced to about 30% of that of +/+ thymi. (B) Schematic representation of Foxn1-lacZ and Foxn1-cre bicistronic message RNA. Allele-specific primers (arrows) were used for quantitative RT-PCR. (C) Comparison of Foxn1 transcript levels from Foxn1^lacZ and Foxn1^cre alleles. The lacZ:cre ratio decreased at postnatal stages, suggesting that the expression of Foxn1 from the Foxn1^lacZ was reduced after birth compared with that from Foxn1^cre allele. P < .001. (D) lacZ and cre mRNA expression were measured with relative quantitative real-time PCR in primary culture thymic stromal cells from Foxn1^lacZ/cre mice at different postnatal ages with or without demethylating drug treatment.