An RNAi Screen Reveals Intestinal Regulators of Branching Morphogenesis, Differentiation, and Stem Cell Proliferation in Planarians

Abstract

SUMMARY Planarians grow and regenerate organs by coordinating proliferation and differentiation of pluripotent stem cells with remodeling of post-mitotic tissues. Understanding how these processes are orchestrated requires characterizing cell type-specific gene expression programs and their regulation during regeneration and homeostasis. To this end, we analyzed the expression profile of planarian intestinal phagocytes, cells responsible for digestion and nutrient storage/distribution. Utilizing RNA interference, we identified cytoskeletal regulators required for intestinal branching morphogenesis, and a modulator of bioactive sphingolipid metabolism, ceramide synthase, required for the production of functional phagocytes. Additionally, we found that a gut-enriched homeobox transcription factor, nkx-2.2, is required for somatic stem cell proliferation, suggesting a niche-like role for phagocytes. Identification of evolutionarily conserved regulators of intestinal branching, differentiation, and stem cell dynamics demonstrates the utility of the planarian digestive system as a model for elucidating the mechanisms controlling post-embryonic organogenesis.

Genome-wide analysis of the bHLH gene family in planarians identifies factors required for adult neurogenesis and neuronal regeneration

“…mitfl-1 was primarily detected in differentiated intestinal cells (supplementary material Fig. S2), and gene knockdown caused severe regeneration abnormalities and dorsal lesions that resulted in death, a phenotype reminiscent of defects observed after the loss of intestinal integrity (Forsthoefel et al, 2012). Consistent with previous reports, gene silencing of tfc15 (Wagner et al, 2011) resulted in no discernible phenotype, whereas myoD RNAi caused regeneration blastema patterning defects (Reddien et al, 2005a).…”

The EGFR signaling pathway controls gut progenitor differentiation during planarian regeneration and homeostasis

“…quaternary and tertiary), which consist of fewer cells, to the most principal branches, which contain a larger number of gastrodermal cells. Notably, this phenotype differs from those described after silencing other genes required for intestinal integrity (Forsthoefel et al, 2012). The impairment of intestinal adhesion, polarity and phagocyte maturation completely compromises gut regeneration and homeostasis, eventually leading to the death of the animal (Forsthoefel et al, 2012).…”

Wnt/Notum spatial feedback inhibition controls neoblast differentiation to regulate reversible growth of the planarian brain

“…Neoblasts are a heterogeneous population that includes both pluripotent cells and distinct subpopulations specified for production of multiple differentiated tissues (Adler et al, 2014;Cowles et al, 2013;Currie and Pearson, 2013;Forsthoefel et al, 2012;Lapan and Reddien, 2012;Marz et al, 2013;Scimone et al, 2011Scimone et al, , 2014avan Wolfswinkel et al, 2014;Vásquez-Doorman and Petersen, 2014;Vogg et al, 2014;Wenemoser et al, 2012). We hypothesized that notum and wnt11-6 might regulate brain cell production by controlling numbers of brain cell progenitors marked by expression of lineage-specific transcription factors.…”

“…Growth from feeding or epimorphic regeneration depends on parenchymal cells termed neoblasts that are the only proliferating cells in adult planarians (Baguñà, 1976;Newmark and Sánchez Alvarado, 2000;Reddien et al, 2005b). Neoblasts are a heterogeneous population containing both adult pluripotent stem cells (Wagner et al, 2011) and more lineage-restricted dividing cells (Adler et al, 2014;Cowles et al, 2013;Currie and Pearson, 2013;Forsthoefel et al, 2012;Lapan and Reddien, 2012;Marz et al, 2013;Scimone et al, 2014aScimone et al, ,b, 2011van Wolfswinkel et al, 2014;Vásquez-Doorman and Petersen, 2014;Vogg et al, 2014;Wenemoser et al, 2012). Tissue removal results in proliferative activation of neoblasts thought to be necessary for production of missing tissue types within the regeneration blastema.…”