A targeting vector was designed to introduce a loxP-flanked neomycin-resistance cassette in reverse transcriptional orientation to intron 17 and an additional loxP site to intron 18. Exon 18 encodes the transmembrane domain of the gene (also called CD148). Targeted animals were bred with BALB/c-background CMV-Cre transgenic female mice to delete the neomycin cassette and exon 18. Transmembrane domain-deleted mice were obtained and characterized. CD148 protein is not detected on any cells of hematopoietic origin by immunoblotting or flow cytometry.