An insight into the sialome of blood-feeding Nematocera

Abstract

Within the Diptera and outside the suborder Brachycera, the blood-feeding habit occurred at least twice, producing the present day sand flies, and the Culicomorpha, including the mosquitoes (Culicidae), black flies (Simulidae), biting midges (Ceratopogonidae) and frog feeding flies (Corethrellidae). Alternatives to this scenario are also discussed. Successful blood-feeding requires adaptations to antagonize the vertebrate's mechanisms of blood clotting, platelet aggregation, vasoconstriction, pain and itching, which are triggered by tissue destruction and immune reactions to insect products. Saliva of these insects provides a complex pharmacological armamentarium to block these vertebrate reactions. With the advent of transcriptomics, the sialomes (from the Greek word sialo = saliva) of at least two species of each of these families have been studied (except for the frog feeders), allowing an insight into the diverse pathways leading to today's salivary composition within the Culicomorpha, having the sand flies as an outgroup. This review catalogs 1288 salivary proteins in 10 generic classes comprising over 150 different protein families, most of which we have no functional knowledge. These proteins and many sequence comparisons are displayed in a hyperlinked spreadsheet that hopefully will stimulate and facilitate the task of functional characterization of these proteins, and their possible use as novel pharmacological agents and epidemiological markers of insect vector exposure.

Figure 1

The 30 kDa antigen/Aegyptin family of blood sucking Nematocera. A) Clustal alignment showing the 2 domain regions (first 20 amino acids excluded). B) Bootstrapped phylogram of the alignment in A. The number near the branches indicates percent bootstrap support after 10,000 trials. The bar at the bottom of the figure indicates 20% amino acid sequence divergence. The sequence names are represented by the first 3 letters of the genus name, followed by two letters of the species name, followed by the GenBank accession number.

Figure 2

Phylogram of the 41 kDa family of mosquitoes, biting midges, black flies and biting midges. The number near the branches indicates percent bootstrap support after 10,000 trials. The bar at the bottom of the figure indicates 20% amino acid sequence divergence. The sequence names are represented by the first 3 letters of the genus name, followed by two letters of the species name, followed by the GenBank accession number, except for some An. gambiae sequences.

Figure 3

Bootstrapped phylogram of the SG1 family of Anophelines. The number near the branches indicates percent bootstrap support after 10,000 trials. The bar at the bottom of the figure indicates 20% amino acid sequence divergence. The sequence names are represented by the first 3 letters of the genus name, followed by two letters of the species name, followed by the GenBank accession number. The An. gambiae sequences are marked with a filled circle.

Fig. 4

Blood-feeding evolution in the Nematocera. Indicated in red are the Null hypothesis (independent evolution of blood-feeding behavior in the Psychomorpha and Culicomorpha) presented in this study, according to Grimaldi and Engel (2005). Numbers at the basal branch indicate the total number of unique sialome protein families not recognizable outside Nematocera that are common to all Nematocera lineages (30 kDa antigen and 41 kDa protein family), followed by the number of all protein families (excluding the orphan proteins) unique to any Nematocera. Below the family branches with available sialome data, the numbers represents the number of protein families unique to the lineage followed by the unique families found in all members (excluding orphan proteins). Notice that the denominators shown at the end of the branches (8, 34, 8 and 24) add to the 74 unique salivary protein families. 4/8 in the sand fly branch indicate that of the 8 unique sand fly protein families, only 4 are shared between Lutzomyia and Phlebotomus. Phylogenetic and divergence date data were obtained from Grimaldi and Engel (2005).