Vascular defects in conditional Reck -deficient mice. (A) 5'-terminal region of the conditional Reck mutant allele before (fl) and after (Δ) CreER-mediated recombination, which leads to the elimination of exon-2 and hence the early termination of translation. (B) Typical genotyping data (left panel) and Reck immunoblot assay (right panel). Reckfl/fl females were mated with CAG-CreER;Reckfl/- males and treated with tamoxifen from 11 dpc; embryos were harvested at E15.5. Yolk sac DNA was subjected to genotyping PCR (left panels; top, Cre primers; bottom, primers flanking Reck exon-2), while the whole embryo proteins were analyzed by immunoblot assay (right panels; top, Reck; bottom, α-tubulin). Note the smaller exon-2 band (lane 2, lower panel) and the absence of Reck protein band (lane 4) in the Cre-positive mouse (lane 2, upper panel). (C) Gross morphology of Reckfl/fl (Cont) and ReckΔ/- (ΔReck) embryos. The ΔReck embryos (i.e., CAG-CreER;Reckfλ/- embryos treated with tamoxifen; right panel) are smaller than the control (i.e., Reckfλ/fl embryos treated with tamoxifen; left panel) and show pale body color and haemorrhage in their heads and abdomen. The frequency of visible haemorrhage was 0% (0/16) in control animals and 100% (14/14) in ΔReck animals in which the hearts were beating. (D) Sagittal sections of the control (left panels) or ΔReck embryos (right panels) stained with H&E. Note the abnormally large blood vessels in the back region (panel 2) and the haemorrhage in the head region (panel 4) found in the ΔReck embryos. Scale bar: C, 1 mm; D, 100 μm.