Generation of the conditional Foxp1 allele. (A) Diagram of the targeting vector containing Foxp1 exons 11 to 14. (B) Southern blot analysis to identify embryonic cell lines carrying the targeted Foxp1 locus. XbaI-digested (left) and SpeI-digested (right) genomic DNA from embryonic stem cells, hybridized to the 2 probes in the short and long arms, respectively. (C) PCR analysis of heterozygous mice confirms germline transmission. Shown is a PCR result indicating the cointegration of the 3′ downstream loxP site (370 bp) and wild-type allele product (280 bp) using primers 1 and 2.