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

Abstract

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. VIDEO ABSTRACT.

Adaptation to low parasite abundance affects immune investment strategy and immunopathological responses of cavefish

“…We demonstrate that cavefish show a more sensitive and prolonged immune response of 58 proinflammatory cytokines towards bacterial endotoxins in -vitro and in -vivo, similar to other 59 vertebrate host species in environments with low biodiversity [13,14]. However, using an image-60 based immune cell clustering approach and single cell RNA sequencing we show that the 61 observed sensitivity towards bacterial endotoxins is accompanied by a reduction of immune cells 62 in the myeloid cell linage, such as monocytes and neutrophils, which are indispensable for 63 proinflammatory processes [15].…”

“…Section preparation and RNA in situ hybridization were performed as previously reported [12] , [13].…”

“…Pachón cavefish population of A. mexicanus shows a more sensitive proinflammatory immune 307 response similar to other vertebrate hosts in environments with low biodiversity [13]. The loss of 308 monocytes and neutrophils, is potentially due to a shift in hematopoiesis from GMP to the EMP 309 and / or CLP lineage, and given that the immune system is costly in terms of fitness [35], it is likely 310 to be a consequence of the loss of parasite diversity in the cave environment.…”

ECM-body: A cell-free 3D biomimetic scaffold derived from intact planarian body

“…Furthermore, the detailed characterization of stem cell types as well as genes involved in tissues homeostasis and organ formation in planarians have also been established (7)(8)(9). It has been shown that the stemness of adult stem cells require physical interactions between the cells and the ECM (10).…”

Somatic drift and rapid loss of heterozygosity suggest small effective population size of stem cells and high somatic mutation rate in asexual planaria

“…Due to the heterogeneity of morphological and cellular features in stem cells, as well as their partial similarity to early post-mitotic committed progeny cells, mitotic molecular markers such as PCNA and H3P or BrdU labeling cannot visualize stem cells completely and exclusively 1,6 . Recently, irradiation and transplantation experiments suggested the surface protein Tetraspanin as a reliable marker for isolation of pluripotent stem cells 7 .…”