Abstract
Schistosomes are parasitic flatworms infecting hundreds of millions of people. These parasites alternate between asexual reproduction in molluscan hosts and sexual reproduction in mammalian hosts; short-lived, water-borne stages infect each host. Thriving in such disparate environments requires remarkable developmental plasticity, manifested by five body plans deployed throughout the parasite's life cycle. Stem cells in Schistosoma mansoni provide a potential source for such plasticity; however, the relationship between stem cells from different life-cycle stages remains unclear, as does the origin of the germline, required for sexual reproduction. Here, we show that subsets of larvally derived stem cells are likely sources of adult stem cells and the germline. We also identify a novel gene that serves as the earliest marker for the schistosome germline, which emerges inside the mammalian host and is ultimately responsible for disease pathology. This work reveals the stem cell heterogeneity driving the propagation of the schistosome life cycle.
Highlights
Flatworms include more than 44,000 parasitic species that form one of the largest groups of metazoan endoparasites (Loker and Hofkin, 2015)
Focusing on the cells that may drive such parasitic life cycles, we study Schistosoma, a parasitic flatworm infecting over 250 million people, which causes the major neglected tropical disease, schistosomiasis (Hoffmann et al, 2014)
Eled appears to inhibit, whereas nanos genes are required for, germ cell differentiation. These results suggest that eled antagonizes the two schistosome nanos homologs: in the soma, it suppresses nanos-2 expression in e-cells in the posterior growth zone (PGZ); in the germline, it inhibits germ cell differentiation. Throughout their life cycles, parasitic flatworms undergo dramatic morphological changes as they switch from free-living, infectious stages to endoparasitic forms residing in different hosts; the cellular basis of this developmental plasticity is largely unknown
Summary
Flatworms include more than 44,000 parasitic species that form one of the largest groups of metazoan endoparasites (Loker and Hofkin, 2015) Their life cycles typically involve asexually and sexually reproducing stages, each with its own distinct body plan and strategy to enhance transmission between multiple hosts (Clark, 1974; Pearce and MacDonald, 2002; Viney and Cable, 2011). Schistosomes are transmitted through snail intermediate and human definitive hosts Their life cycle begins with the parasite egg excreted from the mammalian host into water, releasing a free-swimming miracidium larva. The miracidium penetrates a snail host and transforms into a mother sporocyst that undergoes asexual clonal expansion to produce many daughter sporocysts that leave the mother and colonize other snail tissues These daughters either self-renew to produce more daughters or enter embryogenesis to produce infective cercariae
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