An insight into the transcriptome and proteome of the salivary gland of the stable fly, Stomoxys calcitrans

Abstract

Adult stable flies are blood feeders, a nuisance, and mechanical vectors of veterinary diseases. To enable efficient feeding, blood sucking insects have evolved a sophisticated array of salivary compounds to disarm their host's hemostasis and inflammatory reaction. While the sialomes of several blood sucking Nematocera flies have been described, no thorough description has been made so far of any Brachycera, except for a detailed proteome analysis of a tabanid (Xu et al., 2008). In this work we provide an insight into the sialome of the muscid Stomoxys calcitrans, revealing a complex mixture of serine proteases, endonucleases, Kazal-containing peptides, anti-thrombins, antigen 5 related proteins, antimicrobial peptides, and the usual finding of mysterious secreted peptides that have no known partners, and may reflect the very fast evolution of salivary proteins due to the vertebrate host immune pressure. Supplemental Tables S1 and S2 can be downloaded from http://exon.niaid.nih.gov/transcriptome/S_calcitrans/T1/Sc-tb1-web.xls and http://exon.niaid.nih.gov/transcriptome/S_calcitrans/T2/Sc-tb2-web.xls.

Figure 1

Distribution of the transcripts from the salivary gland cDNA library of S. calcitrans according to functional class.

Figure 2

SDS-PAGE analysis of stable fly salivary gland extract. Lane 1, molecular weight standards; Lane 2, salivary gland extract. Ten putative secreted proteins were identified by N-terminal sequencing after separating proteins extracted from 20 salivary glands by SDS-PAGE. Molecular weight standards and SGE protein bands are shown on the left side. Next are the amino terminal sequences of bands determined by Edman degradation sequencing, and best matches to known proteins. The lower case amino acids represent missing Edman products cysteine and tryptophan. On the right side are the corresponding coding sequence names matching the N-terminal sequence of the protein bands and the number of the EST sequences associated with them. The two bands labeled NTDY… were obtained after removal of pyroglutamate.

Figure 3

Alignment of the Hyp 16 family of Stomoxys calcitrans and other related mosquito salivary proteins. The mosquito species are indicated by 5 letters, the first three being from the genus and the last two from the species names, thus ANOGA for An. gambiae. The number following the letters refers to their GenBank accession number.