Inducible and cell-type–specific activation of

loxP-flanked ROSA26-EGFP allele byMx-cre or lck-cretransgenes. (A) Flow cytometric analysis of EGFP expression in cells from ROSA26-EGFP^f/+ and ROSA26-EGFP^f/+;Mx-cre mice injected with pI-pC. A mouse with excised ROSA26-EGFP allele was used as a positive control. Fluorescence intensity was represented on log scale. (B) The enrichment of thymocytes with excised test allele based on the activated expression of EGFP in ROSA26-EGFP^f/+;Test^f/+;lck-cremouse. (Left) Histogram of EGFP expression in thymocytes of heterozygous mouse with lck-cre (nonshaded) or withoutlck-cre (shaded). M1 and M2 indicate the EGFP⁺and EGFP⁻ fractions of thymocytes from triple-compound mouse that are sorted. (Right) Southern blot analysis for the excision of the test floxed allele. Genomic DNAs were digested withSpeI and BglII. The positions of DNA bands representing WT, floxed, and excised test alleles are indicated.