Characterization of genes expressed in the salivary glands of the tsetse fly, Glossina morsitans morsitans

Salivary gland products of haematophogous insects including tsetse flies (Diptera: Glossinidia) are involved in antihaemostasis to allow for efficient blood feeding. In addition, salivary products of tsetse are thought to indirectly support the metacyclogenesis and eventual transmission of the African trypanosome protozoan parasites to their mammalian hosts. We have previously characterized the major anticoagulant, Tsetse Thrombin Inhibitor (TTI), from salivary extracts, and described molecular aspects of its cDNA from a Glossina morsitans morsitans salivary gland cDNA library. In addition, a family of two related genes with growth factor and adenosine-deaminase motifs (TSGF-1 and TSGF-2) have also been described. Here, we report on the molecular aspects of three different cDNAs and their putative products expressed in salivary glands: cDNAs TAg5, Tsal1 and Tsal2. The full-length transcript encoded by Tsetse Antigen 5 (TAg5) cDNA is 926 bp excluding the poly(A) stretch, and has an open reading frame of 259 amino acids that can encode for a protein of 28 925 Da. The putative product of TAg5 shows extensive similarities to cDNAs characterized from Drosophila (Agr and Agr2) and sandfly Lutzomyia (LuLoAG5). The cDNAs Tsal1 and Tsal2 are predicted to encode for mature proteins of 45 612 Da (399 amino acids) and 43 930 Da (389 amino acids), respectively, and their putative products exhibit over 42% identity to one another. The N terminus of each putative protein contains a hydrophobic region with signal peptide characteristics indicating that they may be secretory in nature. Transcripts specific for TAg5 and Tsal2 genes can be detected in all developmental stages of tsetse while Tsal1 expression is limited to adult and larval stages. A reverse transcription polymerase chain reaction based amplification approach indicates that TAg5 transcipts can be detected from proventriculus and midgut tissues of the fly in addition to salivary glands, while Tsal1 and Tsal2 expression is restricted to salivary gland and proventriculus. The salivary glands of adult males are found to express higher levels of TAg5 and Tsal2 in comparison to females while no significant sex-based difference is observed for Tsal1 expression. The expression of these cDNAs in different tsetse species (G. m. morsitans, Glossina austen/and Glossina fuscipes) shows wide variations.