The salivary secretome of the tsetse fly Glossina pallidipes (Diptera: Glossinidae) infected by salivary gland hypertrophy virus.

Henry M Kariithi,Serap Aksoy,Andrew G Parker,Just M Vlak,Adly M M Abd-Alla,Monique M Van Oers,Ikbal A Ince,Sjef Boeren

doi:10.1371/journal.pntd.0001371

Abstract

BackgroundThe competence of the tsetse fly Glossina pallidipes (Diptera; Glossinidae) to acquire salivary gland hypertrophy virus (SGHV), to support virus replication and successfully transmit the virus depends on complex interactions between Glossina and SGHV macromolecules. Critical requisites to SGHV transmission are its replication and secretion of mature virions into the fly's salivary gland (SG) lumen. However, secretion of host proteins is of equal importance for successful transmission and requires cataloging of G. pallidipes secretome proteins from hypertrophied and non-hypertrophied SGs.Methodology/Principal FindingsAfter electrophoretic profiling and in-gel trypsin digestion, saliva proteins were analyzed by nano-LC-MS/MS. MaxQuant/Andromeda search of the MS data against the non-redundant (nr) GenBank database and a G. morsitans morsitans SG EST database, yielded a total of 521 hits, 31 of which were SGHV-encoded. On a false discovery rate limit of 1% and detection threshold of least 2 unique peptides per protein, the analysis resulted in 292 Glossina and 25 SGHV MS-supported proteins. When annotated by the Blast2GO suite, at least one gene ontology (GO) term could be assigned to 89.9% (285/317) of the detected proteins. Five (∼1.8%) Glossina and three (∼12%) SGHV proteins remained without a predicted function after blast searches against the nr database. Sixty-five of the 292 detected Glossina proteins contained an N-terminal signal/secretion peptide sequence. Eight of the SGHV proteins were predicted to be non-structural (NS), and fourteen are known structural (VP) proteins.Conclusions/SignificanceSGHV alters the protein expression pattern in Glossina. The G. pallidipes SG secretome encompasses a spectrum of proteins that may be required during the SGHV infection cycle. These detected proteins have putative interactions with at least 21 of the 25 SGHV-encoded proteins. Our findings opens venues for developing novel SGHV mitigation strategies to block SGHV infections in tsetse production facilities such as using SGHV-specific antibodies and phage display-selected gut epithelia-binding peptides.

Highlights

Tsetse flies (Glossina sp.) are found exclusively in sub-Saharan Africa and are efficient vectors of African trypanosomes, causative agents of sleeping sickness in humans and nagana in domesticated animals [1,2,3]
The problem is that the production of some species of tsetse such as Glossina pallidipes colonies are vulnerable to infections by a salivary gland hypertrophy virus (SGHV) [9,10,11,12]; which in a proportion of infected flies leads to hypertrophy of the salivary glands and gonadal lesions
The Glossina pallidipes species is found in several African countries and rearing facilities have been established in Kenya, Ethiopia and Tanzania with the aim of strengthening the fly eradication campaigns in African

Summary

Introduction

Tsetse flies (Glossina sp.) are found exclusively in sub-Saharan Africa and are efficient vectors of African trypanosomes, causative agents of sleeping sickness in humans and nagana in domesticated animals [1,2,3]. Tsetse control remains the most feasible management technique to combat trypanosomiasis and the application of the sterile insect technique (SIT) within the concept of area-wide integrated insect management (AW-IPM), has had promising successes [7,8]. This strategy relies heavily on colony mass rearing of flies in contained production facilities. The problem is that the production of some species of tsetse such as Glossina pallidipes colonies are vulnerable to infections by a salivary gland hypertrophy virus (SGHV) [9,10,11,12]; which in a proportion of infected flies leads to hypertrophy (hyperplasia) of the salivary glands (hereafter referred to as SGs) and gonadal lesions. Secretion of host proteins is of equal importance for successful transmission and requires cataloging of G. pallidipes secretome proteins from hypertrophied and nonhypertrophied SGs

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