Rhodopsin orphan GPCR20 interacts with neuropeptides and directs growth, sexual differentiation, and egg production in female
Schistosoma mansoni
Authors: Li Xuesong , Weth Oliver , Haimann Martin , Möscheid Max F. , Huber Theresa S. , Grevelding Christoph G. 
Published: December 2023

Schistosomes are parasitic flatworms that cause schistosomiasis, a neglected tropical disease of worldwide importance. Since standard treatment of schistosomiasis relies on a single drug, praziquantel, alternative drugs are needed. G protein-coupled receptors (GPCRs) represent promising targets for new anthelmintics. Although GPCRs represent a prominent receptor class in schistosomes, functional studies are limited just as knowledge about their ligands. Candidate ligands are neuropeptides acting as neurotransmitters, neuromodulators, or hormones in the nervous system. Transcriptomics studies in
Schistosoma mansoni
indicated that nearly all neuropeptide genes (
Sm_npps
) and a subgroup of GPCRs exhibited a sex- and pairing-dependent expression profile. Among these was the rhodopsin orphan GPCR20 (
Sm
GPCR20), which we characterized in our study. Using a yeast two-hybrid-based approach, we identified specific interactions between
Sm
GPCR20 and two neuropeptides
Sm
NPP26 and
Sm
NPP40. As analyzed by qRT-PCR,
Smgpcr20
,
Smnpp26
, and
Smnpp40
showed sex- and/or pairing-influenced expression. Whole-mount
in situ
hybridization exhibited transcripts of these genes in neuronal cells, subtegumental area, and parenchyma of both sexes. Furthermore, we received indication for co-localization of transcripts of these genes in the anterior “head” region of single-sex females and in particular patterns along the worm body indicating neuronal expression. RNA interference (RNAi) with combinations of double-stranded RNAs against the three genes resulted in reduced egg production. Confocal microscopy revealed morphologic changes in the female gonads. Furthermore, RNAi in first-time paired females caused a reduced length of females after double knockdown of
Sm
GPCR20 and
Sm
NPP26 and changes in the ovary. In addition, we found reduced transcript levels of egg formation-associated and gonad-specifically transcribed genes and the stem-cell marker
nanos-1
. The obtained results suggest that
Sm
NPP26 and
Sm
NPP40 are potential ligands of
Sm
GPCR20 and that this GPCR in combination with both neuropeptides affects egg production, oogenesis, and growth of
S. mansoni
females.

IMPORTANCE

Schistosomes cause schistosomiasis, one of the neglected tropical diseases as defined by the WHO. For decades, the treatment of schistosomiasis relies on a single drug, praziquantel. Due to its wide use, there is justified fear of resistance against this drug, and a vaccine is not available. Besides its biological relevance in signal transduction processes, the class of G protein-coupled receptors (GPCRs) is also well suited for drug design. Against this background, we characterized one GPCR of
Schistosoma mansoni
,
Sm
GPCR20, at the molecular and functional level. We identified two potential neuropeptides (NPPs) as ligands,
Sm
NPP26 and
Sm
NPP40, and unraveled their roles, in combination with
Sm
GPCR20, in neuronal processes controlling egg production, oogenesis, and growth of
S. mansoni
females. Since eggs are closely associated with the pathogenesis of schistosomiasis, our results contribute to the understanding of processes leading to egg production in schistosomes, which is under the control of pairing in this exceptional parasite.