Figure 1 Glycoforms of MUC1. MUC1 is composed of an extracellular domain consisting of a variable number of highly conserved tandem repeats of 20 amino acids (GVTSAPDTRPAPGSTAPPAH), a transmembrane domain, and a cytoplasmic tail domain (CTD) of 69 amino acids in the intracellular domain. Cleavage of a single polypeptide at SEA (sea-urchin sperm protein, enterokinase and agrin) domain results in the two subunits of MUC1, MUC1-N terminus and MUC1-C terminus. They are heterodimerized by non-covalent interactions and anchored to the surface of the cell. Underglycosylated, sialylated, and fully glycosylated forms of MUC1 can be detected by epitope-specific monoclonal antibodies. Recently, we have developed a novel antibody for MUC1 CTD, which we refer to as MAb MUC1-014E.

Figure 2 Schematic representation of secretory mucins. The MUC2 gene is located at the telomeric end of an approximately 400 kb gene cluster on chromosome 11p15.5. MUC2 is oriented from centromere to telomere and is clustered with other secretory mucin genes such as MUC6 and MUC5AC/B (a). Illustration of the monomeric MUC2 protein (b). The 1st tandem repeat (TR) region is Ser, Thr and Pro rich, and comprises 21 repeats of an irregular amino acid motif. The 2nd TR region shows a variable number of tandem repeats (VNTRs) from 51 to 115, with each composed of 23 amino acids. The central repetitive domains are rigid owing to heavy glycosylation, whereas the unique sequences of the N-terminal and C-terminal regions are sparsely glycosylated and protease-sensitive (b). In addition, the unique sequences have numerous Cys residues that link monomers via disulfide bonds to form oligomers (c).

Figure 3 MUC3 expression in normal small intestine. Clear linear staining of the surface of villi in the normal mucosa of the small intestine is a very good positive control for MUC3 immunohistochemistry staining.

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