A family of genes with growth factor and adenosine deaminase similarity are preferentially expressed in the salivary glands of Glossina m. morsitans

A cDNA library constructed from salivary glands of tsetse fly, Glossina mor sitans morsitans (Diptera: Glossinidae), was differentially screened, and t wo related full-length cDNAs were molecularly characterized: tsetse salivar y growth factor, TSGF-1 and TSGF-2. The cDNAs encode for open reading frame s (ORFs) of 494 and 506 aa, respectively, and display an overall 45% amino acid identity and 61% similarity to one another. Both genes are preferentia lly expressed in the salivary glands of male and female adult flies. In add ition to salivary glands, both transcripts can be detected from the gut tis sue. Only transcripts specific for TSGF-2 are detected in ovary and testes tissues of adults as well as in puparia, while neither gene is expressed du ring the larval developmental stages. The N-terminal region of both putativ e proteins contains a hydrophobic sequence with secretory signal peptide ch aracteristics, and analysis of proteins in saliva by Western blot indicates that both are secreted. Western blot analysis indicates that TSGF-1 is syn thesized at significantly higher levels than TSGF-2. The deduced protein se quences of both cDNAs display extensive similarities to two other proteins: insect derived growth factor (IDGF) characterized from Sarcophaga peregrin a with growth-factor activity, and atrial gland specific antigen (AGSA or M DSF) characterized from Apylasia californica. In addition to growth factor similarity, all four related proteins share the evolutionarily conserved am ino acid residues associated with the enzymatic deamination of adenosine, w hich is shown here to be present in salivary gland extracts of tsetse. Whil e both genes are present and expressed in G. m. morsitans and G. p. palpali s, only TSGF-1 is present in G. austeni. We present the molecular character istics of the cDNAs, their genomic arrangement and their regulation of expr ession in different fly tissues and species. We discuss the potential role of these proteins in hemostatis and in African trypanosome transmission by different species of tsetse. (C) 2000 Elsevier Science B.V. All rights rese rved.