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Nature. 2017 May 11;545(7653):238-242. doi: 10.1038/nature22313. Epub 2017 May 3.

Non-equivalence of Wnt and R-spondin ligands during Lgr5+ intestinal stem-cell self-renewal.

Author information

1
Department of Medicine, Stanford University School of Medicine, Stanford, California 94305, USA.
2
Columbia Center for Human Development, Department of Medicine, Division of Digestive and Liver Diseases, Department of Genetics and Development, Columbia University Medical Center, New York 10032, USA.
3
Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California 94305, USA.
4
10x Genomics, Inc., Pleasanton, California 94566, USA.
5
Columbia Center for Translational Immunology, Department of Medicine, Division of Digestive and Liver Diseases, Department of Microbiology and Immunology, Columbia University Medical Center, New York 10032, USA.
6
Department of Genetics, Stanford University School of Medicine, Stanford, California 94305, USA.
7
Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305, USA.
8
Oregon Health &Science University, Department of Cell, Developmental and Cancer Biology, Portland, Oregon 97239, USA.
9
Institute for Stem Cell Biology, Stanford University School of Medicine, Stanford, California 94305, USA.
10
Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
11
Department of Obstetrics and Gynecology, Stanford University School of Medicine, Stanford, California 94305, USA.

Abstract

The canonical Wnt/β-catenin signalling pathway governs diverse developmental, homeostatic and pathological processes. Palmitoylated Wnt ligands engage cell-surface frizzled (FZD) receptors and LRP5 and LRP6 co-receptors, enabling β-catenin nuclear translocation and TCF/LEF-dependent gene transactivation. Mutations in Wnt downstream signalling components have revealed diverse functions thought to be carried out by Wnt ligands themselves. However, redundancy between the 19 mammalian Wnt proteins and 10 FZD receptors and Wnt hydrophobicity have made it difficult to attribute these functions directly to Wnt ligands. For example, individual mutations in Wnt ligands have not revealed homeostatic phenotypes in the intestinal epithelium-an archetypal canonical, Wnt pathway-dependent, rapidly self-renewing tissue, the regeneration of which is fueled by proliferative crypt Lgr5+ intestinal stem cells (ISCs). R-spondin ligands (RSPO1-RSPO4) engage distinct LGR4-LGR6, RNF43 and ZNRF3 receptor classes, markedly potentiate canonical Wnt/β-catenin signalling, and induce intestinal organoid growth in vitro and Lgr5+ ISCs in vivo. However, the interchangeability, functional cooperation and relative contributions of Wnt versus RSPO ligands to in vivo canonical Wnt signalling and ISC biology remain unknown. Here we identify the functional roles of Wnt and RSPO ligands in the intestinal crypt stem-cell niche. We show that the default fate of Lgr5+ ISCs is to differentiate, unless both RSPO and Wnt ligands are present. However, gain-of-function studies using RSPO ligands and a new non-lipidated Wnt analogue reveal that these ligands have qualitatively distinct, non-interchangeable roles in ISCs. Wnt proteins are unable to induce Lgr5+ ISC self-renewal, but instead confer a basal competency by maintaining RSPO receptor expression that enables RSPO ligands to actively drive and specify the extent of stem-cell expansion. This functionally non-equivalent yet cooperative interaction between Wnt and RSPO ligands establishes a molecular precedent for regulation of mammalian stem cells by distinct priming and self-renewal factors, with broad implications for precise control of tissue regeneration.

PMID:
28467820
PMCID:
PMC5641471
DOI:
10.1038/nature22313
[Indexed for MEDLINE]
Free PMC Article

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