Gene-KO strategies and genomic structure of MASP genes. (A) Single, double, triple, and quadruple KOs of MASPs were isolated from the claudin-2 (CLDN2)-KO MDCK II (Ctrl) cell clone. (B) Genomic structure of KO cells. Two gRNAs were simultaneously introduced to the cells to induce large deletions. The sequences of gRNAs (red) and genome sequences of the KO clones are shown. The deleted regions of TMPRSS1 (TP1) and TMPRSS4 (TP4) contain the sequences encoding transmembrane region, which is supposed to be critical for proper localization and function of these genes. For TMPRSS14 (TP14) and PRSS8(P8), the first exon with a start codon (green) was removed.