RNA Seq analysis of gene expression during Schmidtea mediterranea embryogenesis, including yolk and adult samples

Planarian neoblasts are pluripotent, adult somatic stem cells and lineage-primed progenitors required for the production and maintenance of all differentiated cell types, including the germline. Neoblasts, originally defined by Harriet Randolph as undifferentiated, embryonic-like cells residing in the adult parenchyma, are frequently compared to embryonic stem cells yet their developmental origin remains obscure. We investigated the provenance of neoblasts during S. mediterranea embryogenesis, and report that neoblasts arise from an anarchic, cycling piwi-1+ population that is wholly responsible for production of all temporary and definitive organs during embryogenesis. Early embryonic piwi-1+ cells are molecularly and functionally distinct from neoblasts: they express unique cohorts of early embryo enriched transcripts and the cells behave differently than neoblasts in cell transplantation assays. Neoblast lineages, established as organogenesis commences, persist into adulthood, where they act as agents of tissue homeostasis and regeneration.