Isoform 1 and isoform 2-6 share the first 17 amino acid residues that correspond to the signal sequence. Detected in terminal tubule cells of the submandibular gland (at protein level). Expressed in submandibular salivary glands of 3-day-old males but not adults. Expression in adult submandibular glands is restricted to females. Isoform 5 is expressed in both 3-day-old and adult sublingual glands. N-glycosylated.