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 malari a vector mosquito Anopheles gambiae. The predicted 122-residue protein cons ists of a central core of seven repeating TTTTVAP motifs flanked by hydroph obic 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 mo squitoes. A length polymorphism and in situ hybridization were used to gene tically and cytogenetically map AgMuc1 to division 7A of the right arm of t he second chromosome. The subcellular localization of the encoded protein i n tissue culture cells was examined by using a baculovirus vector to expres s AgMuc1 protein tagged with the green fluorescent protein (GFP), The resul ts indicated that this protein is found at the cell surface and that both h ydrophobic domains are required for cell surface targeting. We propose that AgMuc1 is an abundant mucin-like protein that lines the surface of the mid gut microvilli, potentially protecting the intestinal epithelium from the p roteinase-rich environment of the gut lumen. An intriguing possibility is t hat, as an abundant surface protein, AgMuc1 may also interact with the mala ria parasite during its invasion of the mosquito midgut.