Prospectively Isolated Tetraspanin+ Neoblasts Are Adult Pluripotent Stem Cells Underlying Planaria Regeneration

Proliferating cells known as neoblasts include pluripotent stem cells (PSCs) that sustain tissue homeostasis and regeneration of lost body parts in planarians. However, the lack of markers to prospectively identify and isolate these adult PSCs has significantly hampered their characterization. We used single-cell RNA sequencing (scRNA-seq) and single-cell transplantation to address this long-standing issue. Large-scale scRNA-seq of sorted neoblasts unveiled a novel subtype of neoblast (Nb2) characterized by high levels of PIWI-1 mRNA and protein and marked by a conserved cell-surface protein-coding gene, tetraspanin 1 (tspan-1). tspan-1-positive cells survived sub-lethal irradiation, underwent clonal expansion to repopulate whole animals, and when purified with an anti-TSPAN-1 antibody, rescued the viability of lethally irradiated animals after single-cell transplantation. The first prospective isolation of an adult PSC bridges a conceptual dichotomy between functionally and molecularly defined neoblasts, shedding light on mechanisms governing in vivo pluripotency and a source of regeneration in animals. [Display omitted] [Display omitted] •piwi-1 RNA and protein expression defined spectrum of functional neoblast states•scRNA-seq defined 12 neoblast sub-types; sub-type Nb2 contains pluripotent stem cells•Transplantation of single TSPAN-1+ Nb2 cells rescued lethally irradiated animals•Nb2 transcriptome differs during homeostasis, sublethal irradiation, and regeneration Transplantation of a single pluripotent neoblast can restore regenerative ability and viability to lethally irradiated Planaria.