A cell surface mucin specifically expressed in the midgut of the malaria mosquito Anopheles gambiae

An invertebrate intestinal mucin gene, AgMuc1, was isolated from the malaria vector mosquito Anopheles gambiae. The predicted 122-residue protein consists of a central core of seven repeating TTTTVAP motifs flanked by hydrophobic N- and C-terminal domains. This structure is similar to that of mucins that coat the protozoan parasite Trypanosoma cruzi. Northern blot analysis indicated that the gene is expressed exclusively in the midgut of adult mosquitoes. A length polymorphism and in situ hybridization were used to genetically and cytogenetically map AgMuc1 to division 7A of the right arm of the second chromosome. The subcellular localization of the encoded protein in tissue culture cells was examined by using a baculovirus vector to express AgMuc1 protein tagged with the green fluorescent protein (GFP). The results indicated that this protein is found at the cell surface and that both hydrophobic domains are required for cell surface targeting. We propose that AgMuc1 is an abundant mucin-like protein that lines the surface of the midgut microvilli, potentially protecting the intestinal epithelium from the proteinase-rich environment of the gut lumen. An intriguing possibility is that, as an abundant surface protein, AgMuc1 may also interact with the malaria parasite during its invasion of the mosquito midgut.