Identifying and validating the presence of Guanine-Quadruplexes (G4) within the blood fluke parasite Schistosoma mansoni.

Abstract

BackgroundSchistosomiasis is a neglected tropical disease that currently affects over 250 million individuals worldwide. In the absence of an immunoprophylactic vaccine and the recognition that mono-chemotherapeutic control of schistosomiasis by praziquantel has limitations, new strategies for managing disease burden are urgently needed. A better understanding of schistosome biology could identify previously undocumented areas suitable for the development of novel interventions. Methodology/Principal findingsHere, for the first time, we detail the presence of G-quadruplexes (G4) and putative quadruplex forming sequences (PQS) within the Schistosoma mansoni genome. We find that G4 are present in both intragenic and intergenic regions of the seven autosomes as well as the sex- defining allosome pair. Amongst intragenic regions, G4 are particularly enriched in 3 UTR regions. Gene Ontology (GO) term analysis evidenced significant G4 enrichment in the wnt signalling pathway (p<0.05) and PQS oligonucleotides synthetically derived from wnt-related genes resolve into parallel and hybrid G4 motifs as elucidated by circular dichroism (CD) spectroscopy. Finally, utilising a single chain anti-G4 antibody called BG4, we confirm the in situ presence of G4 within both adult female and male worm nuclei. Conclusion/SignificanceThese results collectively suggest that G4-targeted compounds could be tested as novel anthelmintic agents and highlights the possibility that G4-stabilizing molecules could be progressed as candidates for the treatment of schistosomiasis. Author SummarySchistosoma mansoni causes schistosomiasis, a parasitic disease that affects millions of people living in resource-deprived areas of developing countries. No vaccine exists and the current drug treatment has limitations, notably inefficacy against the larval stages of the parasite. New drugs are, therefore, needed to sustainably control schistosomiasis. A further understanding of parasite biology will uncover new targets and lead to the development of novel therapies. Here, we identify the presence of G-Quadruplexes (G4s) in S. mansoni. G4s are four-stranded DNA structures that can affect gene function and, to date, have not been previously found in any parasitic helminth. Computational analysis predicted potential G4 folding sequences within the S. mansoni genome, several of which were confirmed to fold by circular dichroism spectroscopy. Analysis of G4-containing protein coding genes found an enrichment within the wnt signalling pathway, a developmental pathway crucial for axial development in the parasite. Additionally, G4s could be detected within adult worms using a fluorescent antibody that selectively recognises quadruplex structures in nucleic acids. This research describes the presence of a previously unknown structure within the parasite, which could present a new target for developing novel treatments.