Single-cell analysis of stem cells driving the parasitic life cycle of Schistosoma

Schistosomes are parasitic flatworms infecting hundreds of millions of people. These parasites alternate between asexual reproduction in molluscan intermediate hosts and sexual reproduction in mammalian definitive hosts. Thriving in such disparate environments requires remarkable developmental plasticity, manifested by five different body plans deployed throughout the life cycle. Stem cells found in both larval and adult schistosomes provide a potential cellular source for this plasticity. To understand the relationships between stem cells from different life-cycle stages, we used single-cell transcriptional profiling. We identified four stem cell classes and validated their distinct spatiotemporal patterns using in situ hybridization. Characterizing these cells at major developmental transitions revealed larvally derived stem cells that are passed to the intramammalian stage; distinct subsets of these cells appear to be the source of either adult somatic stem cells or the germline. This work demonstrates that stem cell heterogeneity drives the propagation of the schistosome life cycle.