Temporally controlled, tamoxifen-dependent recombination in HSC-SCL-Cre-ER^T embryos. (A) The 6E5/Cre-ER^T/3′enh construct used to generate HSC-SCL-Cre-ER^T transgenic mice. The 6E5 genomic fragment containing the SCL exon 4 promoter combined with a 5.5-kb Scl 3′ enhancer sequence was used to control expression of Cre-ER^T. White, light gray, and dark gray boxes represent introns, untranscribed exon, and transcribed exon sequences, respectively. (B) Schematic drawing of the transgenic system used in this study. Upon tamoxifen (TAM) treatment, the Cre-ER^T recombinase is translocated and the stop-cassette is removed, inducing expression of Eyfp or lacZ. (C) LacZ staining of E12.5 HSC-SCL-Cre-ER^T;R26R embryos revealed positive staining of the fetal liver and scattered LacZ-positive cells throughout the embryo. (D) View on the visceral side of the E12.5 yolk sac, showing spindle-shaped LacZ-positive endothelial cells within blood vessels. (E) Latero-medial view onto the fetal liver. (C-E) LacZ whole-mount staining after maternal tamoxifen injections E9.5 0.5 mg, E10.5 1 mg, and E11.5 2 mg.