Establishing the VWF^h28knockin mouse strain. (A) E14 mouse ES cells were targeted with the depicted construct, and a total of 380 clones were screened by PCR. (B) Genomic DNA samples of the positive ES clones were digested with restriction enzyme KpnI and confirmed by Southern blot using a probe designed in the 3′ homology arm. The WT allele appears as a 6.2-kb band whereas the targeted allele appears as a 7.8-kb band. TK, thymidine kinase gene.