Characterization of the Sialokinin I gene encoding the salivary vasodilator of the yellow fever mosquito, Aedes aegypti

Abstract

The gene encoding sialokinin I, the principal vasodilatory peptide of Aedes aegypti, has been isolated and characterized. Degenerate oligonucleotide primers based on peptide amino acid sequence were used to amplify a gene fragment from messenger RNA (mRNA) isolated from female salivary glands. The amplification product was used to probe a salivary gland complementary DNA (cDNA) library, and a number of corresponding cDNAs were isolated and their primary sequence determined. Analysis of the conceptual translation product of a 406-bp cDNA indicates that sialokinin I is expressed as a preprosialokinin and is subsequently post-translationally processed to the active peptide. Northern analysis revealed a 490-bp transcription product expressed exclusively in female salivary glands, and hybridization in situ of probes to RNA in whole tissues localized gene expression to the medial lobe of female salivary glands. Screening of an Ae. aegypti genomic library with the cDNA resulted in the isolation of a clone containing the gene, designated Sialokinin I (Sia I). Comparison of the cDNA with the genomic clone reveals two introns of 62 bp and 833 bp. Primer extension analysis showed that several transcription initiation sites are present. Southern analysis of genomic DNA shows that Sia I is most probably a single-copy gene. Similarities of the Sia I gene product with other genes are confined to the region encoding the active decapeptide.

Expression and Functional Characterization of aDrosophila Neuropeptide Precursor with Homology to Mammalian Preprotachykinin A

“…As a consequence, the endogenous ligands for NKD and DTKR are not known. A tachykinin precursor cDNA has recently been cloned from the mosquito A. aegypti that contains only a single tachykinin-like peptide, sialokinin I (24). Sialokinins are thought to be released into mosquito saliva and thus enter the host at a blood meal.…”

Genetics of Mosquito Vector Competence

“…Apyrases prevent platelet aggregation by converting ATP and ADP to AMP, eliminating the signal (ADP) for aggregation (30,146,199,225). Vasodilation is promoted by the secretion of sialokinins, tachykinin-like molecules, in A. aegypti and catechol oxidase/ salivary peroxidase in A. albimanus (7,29,194,197,198,200). In A. aegypti, the AFXa gene encodes a serine protease inhibitor-like molecule that is directed against factor Xa of the coagulation pathway, thereby acting as an anticoagulant (230,233).…”

“…These molecules are secreted principally by female mosquitoes and are synthesized in specialized regions (the distal lateral and medial lobes) of the salivary glands (7,104,225). Male mosquitoes, which are incapable of blood feeding and feed only on nectar, lack these specialized regions.…”

Blocking malaria parasite invasion of mosquito salivary glands

“…The proximal regions of the lateral lobes in females express and secrete salivary gland products such as amylases and α1-4 glucosidase that are involved in sugar feeding, and these lobes appear to overlap functionally the male salivary glands (James, 1994;Arcá et al, 1999). In contrast, the medial lobe and distal-lateral lobes express genes whose products such as apyrases, anticoagulants and vasodilatory agents are involved in hematophagy (Champagne et al, 1995;Smartt et al, 1995;Beerntsen et al, 1999;Stark and James, 1998;Arcá et al, 1999).…”

“…The proximal regions of the lateral lobes in females express and secrete salivary gland products such as amylases and α1-4 glucosidase that are involved in sugar feeding, and these lobes appear to overlap functionally the male salivary glands (James, 1994;Arcá et al, 1999). In contrast, the medial lobe and distal-lateral lobes express genes whose products such as apyrases, anticoagulants and vasodilatory agents are involved in hematophagy (Champagne et al, 1995;Smartt et al, 1995;Beerntsen et al, 1999;Stark and James, 1998;Arcá et al, 1999).In addition to their gene expression characteristics, the surface properties of the different salivary gland lobes are also variable. A number of studies with lectins and monoclonal antibodies raised to whole salivary glands show differential binding of these agents to the lobes of the female glands (Perrone et al, 1986;Barreau et al, 1995Barreau et al, , 1999.…”