The role of small RNAs in Strongyloides parasitism

: (Alternative Format Thesis)

Abstract

Strongyloides stercoralis is a gastrointestinal parasitic nematode that infects approximately 600 million people worldwide. The closely related species S. ratti and S. venezuelensis which are parasites of rats can be used as laboratory models. Uniquely, the Strongyloides life cycle alternates between genetically identical parasitic and free-living generations that can be maintained in the laboratory. Direct comparison of the parasitic and free-living stages thus enables an opportunity to unravel the genetic basis of parasitism. Here, we explore the role of small non-coding RNAs (sRNAs) which are important for regulating genes and transposons via post-transcriptional gene silencing. Parasitic nematodes express sRNAs to regulate their own gene expression as well as expressing sRNAs that are encapsulated and secreted within exosome-like vesicles (ELVs) into the host. Three main sRNA pathways have been described including microRNAs (miRNAs), small interfering RNAs (siRNAs) and piwi-interacting RNA (piRNAs). The piRNA class of sRNAs which are important in targeting and regulating transposon activity are proposed to have been lost outside of clade V nematodes, including Strongyloides. In the first chapter, we identify and classify sRNAs expressed by both the parasitic and free-living life cycles of S. ratti and reveal a parasite-associated class of 21-22 nucleotide (nt) long sRNAs with a 5’ uracil (21-22Us). The parasite-associated 21-22Us show a resemblance to the piRNAs of C. elegans. We hypothesise the 21-22Us compensate for the loss of piRNAs in clade IV nematodes and propose that they are either directly related to parasitism or features associated with the parasitic life cycle. In the second chapter, we investigate sRNAs that are secreted into the host via ELVs and taken up by intestinal epithelial cells. Analysis of sRNAs in ELVs identified a class of sRNAs under 16nts termed tiny RNAs (tyRNAs), explored for the first time in nematodes. The ELV-tyRNAs, secreted by S. ratti and S. venezuelensis were predicted to target host genes related to immunity, inflammation and muscle contraction, a mechanism used by Strongyloides to evade host immune system and persist within the host. Our findings provided an insight into host-parasite interactions, and how we can use this as potential diagnostic markers for parasite infection. Finally, in the third chapter, we investigate gene expression changes in the gastrointestinal tract of rats infected with S. ratti. We identify genes that are upregulated during infection, some of which are associated with immunity and muscle contraction. Additionally, we utilise a mouse embryo intestinal model that undergoes peristalsis to investigate the impact of Strongyloides on host intestinal contractions. Overall, our analysis provides insights into the strategies used by Strongyloides to manipulate the anti-nematode responses in the host.

Date of Award	27 Mar 2024
Original language	English
Awarding Institution	University of Bath
Supervisor	Vicky Hunt (Supervisor), Jean Van Den Elsen (Supervisor) & Maisem Laabei (Supervisor)