The Anopheles gambiae salivary glands: transcriptome analysis and tissue-specific promoters.

The salivary glands of haematophagous arthropods express a large variety of bioactive molecules that play important roles in blood feeding and parasite transmission. With the final aim to identify secreted proteins and sporozoite receptor(s) we used a selective cloning strategy that allowed for the identification of several Anopheles gambiae salivary genes. We are currently progressing on the analysis of the A. gambiae salivary gland transcriptome and we are assemblying a catalogue of genes which are specifically expressed in the salivary glands of this mosquito. Surprisingly, a significant proportion of the salivary genes identified so far appeared to encode putative polypeptides with no similarity to known proteins. For this reason we initiated expression of recombinant salivary proteins in order to set up functional assays and evaluate their effect on haemostasis and/or on the immune response of the host. In the effort to identify an efficient salivary promoter, which could be useful for studies on mosquito-parasite interactions in transgenic mosquitoes, we tested the 5’upstream regions of the A. gambiae AgApy and D7r4 genes in Anopheles stephensi and in the fruitfly Drosophila melanogaster. An 800 bp AgApy promoter fragment was able to drive weak transgene expression in the salivary glands of both the fruitfly and the mosquito; however, the lobe-specific pattern of expression observed in A. stephensi did not match the A. gambiae endogenous pattern. Conversely, different results were observed in the fruitfly and in the mosquito with the D7r4 promoter: efficient expression of the reporter gene was obtained in the Drosophila salivary glands whereas transgene expression was hardly detectable in A. stephensi. More recently we have obtained a few A. gambiae lines transformed with a larger fragment (approx. 2.5 kb) of the AgApy promoter driving the E. coli beta-galactosidase gene; these lines are presently under analysis.