Dramatic changes in gene expression in different forms of Crithidia fasciculata reveal potential mechanisms for insect-specific adhesion in kinetoplastid parasites.

John N Filosa,Wesley C Warren,Chad Tomlinson,Megan L Povelones,Gordon Ruthel,Michael Povelones,Corbett T Berry,Peter J Myler,Stephen M Beverley,Elizabeth A Dudkin

doi:10.1371/journal.pntd.0007570

Abstract

Kinetoplastids are a group of parasites that includes several medically-important species. These human-infective species are transmitted by insect vectors in which the parasites undergo specific developmental transformations. For each species, this includes a stage in which parasites adhere to insect tissue via a hemidesmosome-like structure. Although this structure has been described morphologically, it has never been molecularly characterized. We are using Crithidia fasciculata, an insect parasite that produces large numbers of adherent parasites inside its mosquito host, as a model kinetoplastid to investigate both the mechanism of adherence and the signals required for differentiation to an adherent form. An advantage of C. fasciculata is that adherent parasites can be generated both in vitro, allowing a direct comparison to cultured swimming forms, as well as in vivo within the mosquito. Using RNAseq, we identify genes associated with adherence in C. fasciculata. As almost all of these genes have orthologs in other kinetoplastid species, our findings may reveal shared mechanisms of adherence, allowing investigation of a crucial step in parasite development and disease transmission. In addition, dual-RNAseq allowed us to explore the interaction between the parasites and the mosquito. Although the infection is well-tolerated, anti-microbial peptides and other components of the mosquito innate immune system are upregulated. Our findings indicate that C. fasciculata is a powerful model system for probing kinetoplastid-insect interactions.

Highlights

Kinetoplastids are eukaryotic parasites, some of which are agents of important tropical diseases such as Human African Trypanosomiasis, Chagas Disease, and Leishmaniasis
We have compared gene expression profiles of motile, non-adherent C. fasciculata to those of C. fasciculata adhered to non-living substrates and those attached to the hindgut of mosquitoes
These results establish a new, robust system to explore the interaction between kinetoplastids and their insect hosts

Summary

Introduction

Kinetoplastids are eukaryotic parasites, some of which are agents of important tropical diseases such as Human African Trypanosomiasis, Chagas Disease, and Leishmaniasis. While the cell biology of these parasites has been studied intensively for decades, many of the life cycle stages that develop in the insect vector are the least well characterized. This is because certain developmental forms are not amenable to cultivation and their abundance or location in the insect complicates their isolation and analysis. With the exception of members of the Vianna subgenus, such as L. braziliensis, all Leishmania species undergo a similar developmental program within the fly [1] They enter during blood feeding and proliferate in the midgut as promastigotes, which divide as rosettes with their flagella oriented towards the center [2, 3]. Accumulating parasites compromise the function of the valve, allowing parasites to migrate beyond it and enter the proboscis where they can be transmitted during the bloodmeal [3]

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Conclusion