A loxP site was inserted upstream of exon 15. A floxed neomycin resistance cassette was inserted downstream of exon 18. Cre-mediated recombination removed exons 15 through 18 (encoding part of the spacer region and the complete 3 cysteine-rich (CR) repeat motifs) and the selection cassette.
RT-PCR analysis followed by direct sequencing showed that while exons 15-18 were successfully deleted, the COOH-terminal CUB domain was transcribed via in-frame coding in homozygous mutant platelets. Immunostaining using anti-CR specific antibody confirmed a complete absence of the 3 CR repeats but conservation of the CUB domain in mutant platelets. The soluble form of SCUBE1 protein was undetectable in mutant mice.