Gene silencing by RNA interference in Sarcoptes scabiei: a molecular tool to identify novel therapeutic targets

Deepani D Fernando,Martha Zakrzewski,Edward J Marr,Katja Fischer,Simone L Reynolds,Stewart T G Burgess

doi:10.1186/s13071-017-2226-1

Abstract

BackgroundScabies is one of the most common and widespread parasitic skin infections globally, affecting a large range of mammals including humans, yet the molecular biology of Sarcoptes scabiei is astonishingly understudied. Research has been hampered primarily due to the difficulty of sampling or culturing these obligatory parasitic mites. A further and major impediment to identify and functionally analyse potential therapeutic targets from the recently emerging molecular databases is the lack of appropriate molecular tools.MethodsWe performed standard BLAST based searches of the existing S. scabiei genome databases using sequences of genes described to be involved in RNA interference in Drosophila and the mite model organism Tetranychus urticae. Experimenting with the S. scabiei mu-class glutathione S-transferase (SsGST-mu1) as a candidate gene we explored the feasibility of gene knockdown in S. scabiei by double-stranded RNA-interference (dsRNAi).ResultsWe provide here an analysis of the existing S. scabiei draft genomes, confirming the presence of a double stranded RNA (dsRNA) - mediated silencing machinery. We report for the first time experimental gene silencing by RNA interference (RNAi) in S. scabiei. Non-invasive immersion of S. scabiei in dsRNA encoding an S. scabiei glutathione S-transferase mu-class 1 enzyme (SsGST-mu1) resulted in a 35% reduction in the transcription of the target gene compared to controls.ConclusionsA series of experiments identified the optimal conditions allowing systemic experimental RNAi without detrimental side effects on mite viability. This technique can now be used to address the key questions on the fundamental aspects of mite biology and pathogenesis, and to assess the potential therapeutic benefits of silencing S. scabiei target genes.

Highlights

Scabies is one of the most common and widespread parasitic skin infections globally, affecting a large range of mammals including humans, yet the molecular biology of Sarcoptes scabiei is astonishingly understudied
It is a skin disease that affects worldwide, primarily economically disadvantaged populations [3,4,5,6]. It is common in the tropics and here the initial epidermal skin infections with parasitic mites often escalate into complex secondary infections with mite-associated bacterial pathogens, potentially causing serious subsequent sequelae
We developed a non-invasive RNA interference (RNAi) methodology specific for S. scabiei and demonstrate the successful experimental gene-silencing of SsGST-mu1 in S. scabiei var. suis following immersion in complementary double stranded RNA (dsRNA)

Summary

Introduction

Scabies is one of the most common and widespread parasitic skin infections globally, affecting a large range of mammals including humans, yet the molecular biology of Sarcoptes scabiei is astonishingly understudied. A few broad spectrum anti-parasitic drugs are currently in use to treat scabies [16, 17], but these often fail to control the disease because of their limited ovicidal activity and their short half-lives [18, 19]. This dictates multiple treatments and combining topical and systemic drugs, which causes considerable management issues [19]. Scabies (and mange) remains a small, understudied research field

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