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. 2015 May 12;4(5):759-67.
doi: 10.1016/j.stemcr.2015.03.003. Epub 2015 Apr 16.

Frizzled7 functions as a Wnt receptor in intestinal epithelial Lgr5(+) stem cells

Dustin J Flanagan  1 , Toby J Phesse  2 , Nick Barker  3 , Renate H M Schwab  1 , Nancy Amin  1 , Jordane Malaterre  4 , Daniel E Stange  5 , Cameron J Nowell  2 , Scott A Currie  1 , Jarel T S Saw  1 , Eva Beuchert  1 , Robert G Ramsay  4 , Owen J Sansom  6 , Matthias Ernst  2 , Hans Clevers  5 , Elizabeth Vincan  7
Affiliations

Frizzled7 functions as a Wnt receptor in intestinal epithelial Lgr5(+) stem cells

Dustin J Flanagan et al. Stem Cell Reports. .

Abstract

The mammalian adult small intestinal epithelium is a rapidly self-renewing tissue that is maintained by a pool of cycling stem cells intermingled with Paneth cells at the base of crypts. These crypt base stem cells exclusively express Lgr5 and require Wnt3 or, in its absence, Wnt2b. However, the Frizzled (Fzd) receptor that transmits these Wnt signals is unknown. We determined the expression profile of Fzd receptors in Lgr5(+) stem cells, their immediate daughter cells, and Paneth cells. Here we show Fzd7 is enriched in Lgr5(+) stem cells and binds Wnt3 and Wnt2b. Conditional deletion of the Fzd7 gene in adult intestinal epithelium leads to stem cell loss in vivo and organoid death in vitro. Crypts of conventional Fzd7 knockout mice show decreased basal Wnt signaling and impaired capacity to regenerate the epithelium following deleterious insult. These observations indicate that Fzd7 is required for robust Wnt-dependent processes in Lgr5(+) intestinal stem cells.

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Figures

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Graphical abstract
Figure 1
Figure 1
Fzd Expression in the Intestinal Epithelium (A) Immunohistochemical analysis of EGFP expression in the intestinal epithelium of Lgr5EGFP-IRES-CreERT2 showing highest expression in the CBC (black arrowheads) between the Paneth cells (∗) and decreasing gradient to dim daughter cells (yellow arrowheads). Scale bar represents 50 μm. (B) Crypt cells isolated from Lgr5EGFP-IRES-CreERT2 mice were arbitrarily sorted into five populations (5+ highest to 1+ lowest EGFP expression). Fzd expression (Agilent array) in each sorted population was compared with the 5+ (CBC) fraction. (C) Histological analysis of LacZ activity showing recombined (black arrowheads) and non-recombined (red arrowheads) crypt-villi in the intestinal epithelium of Lgr5Cre;LacZ and Lgr5Cre;Fzd7fl/fl;LacZ mice at 1 month post-induction. The number of crypts with recombined CBC cells was scored and is shown as a percentage of total crypts counted (mean ± SEM, ∗p < 0.05, n = 4 mice). Bracket indicates crypt domain. Scale bar represents 100 μm. (D) Representative histological images of LacZ activity showing crypts with recombined (black arrowheads) and non-recombined (red arrowheads) CBC cells in intestinal crypts of AhCre;Fzd5fl/fl;LacZ and AhCre;Fzd7fl/fl;LacZ mice at 1 day post-induction. The number of crypts with recombined CBC cells was scored and shown as a percentage of total crypts counted (mean ± SEM, ∗p < 0.05, n = 4 mice). Bracket indicates crypt domain. Scale bar represents 100 μm. (E) Gene expression (qRT-PCR) analysis on crypts isolated from AhCre;Fzd7fl/fl;LacZ or AhCre;Fzd5fl/fl;LacZ mice at 1 day post-induction (CreInd) compared with controls (Cre) (mean ± SEM, ∗p < 0.05, n = 3 mice). (F) Immunohistochemical analysis of PCNA expression to detect cycling cells (green arrowheads) and enumeration of the number of cycling cells located between Paneth cells in the intestinal crypts of induced AhCre;Fzd7fl/fl;LacZ (Cre+ βNF) and Fzd7fl/fl;LacZ (Cre neg βNF) and non-induced AhCre;Fzd7fl/fl;LacZ (Cre+ Cont) mice (mean ± SEM, ∗p < 0.05, n = 3 mice). Bracket indicates crypt domain. Scale bar represents 50 μm. See also Figures S1 and S2.
Figure 2
Figure 2
Fzd7 Is Required for Maintenance of Organoids (A) Representative differential interference contrast (DIC) images of intestinal organoids from AhCreFzd7fl/fl mice showing crypt atrophy (arrow) and organoid death (#) after treatment with βNF; and rescue with LiCl or CHIR99021 added 1 day after βNF; green arrowheads indicate examples of healthy organoids. Scale bar represents 100 μm. (B) MTT cell viability assay 3 days after passage of vehicle (DMSO) and induced (βNF-treated) organoids (mean ± SEM,∗p < 0.05, n = 3 mice). (C) Gene expression (qRT-PCR) analysis of organoids at 2 days post-induction (βNF) compared with controls (DMSO) (mean ± SEM, ∗p < 0.05, n = 3 mice). (D) Immunofluorescence analysis of E-cadherin (green) and Lysozyme (red) expression in induced (βNF) and control (DMSO) organoid crypts of AhCreFzd7fl/fl mice showing Paneth cell (∗) and CBC (arrowheads) positioning (nuclei blue, DAPI). Scale bar represents 50 μm. (E) PCRs to detect the Fzd7 mutant knockin allele (Fzd7 Mut) and recombined product after Fzd7 gene deletion (DP), AhCre transgene (AhCre), and a region of chromosome 1 close to Fzd7 locus (Chr1), in genomic DNA extracted from organoids established from three AhCreFzd7fl/fl mice (M1, M2, M3) at 2 days post-induction (PI). See also Figure S3.
Figure 3
Figure 3
Impaired Intestine Epithelium Regeneration in Fzd7 KO Mice (A) Immunohistochemical analysis of PCNA expression (cycling cells) in the small intestine epithelium of non-irradiated (not IRR) mice and at indicated times post-irradiation (post-IRR). Brackets indicate crypt domain. Efficiency of regeneration was quantified by counting the number of regenerating crypts per intestine cross-section at 70 hr post-IRR (mean ± SEM, ∗p < 0.05, n ≥ 5 mice). Scale bar represents 50 μm. (B) Wnt target gene expression (qRT-PCR) in isolated intestinal crypts 70 hr post-IRR (mean ± SEM, ∗p < 0.05, n = 6 mice). (C) Immunohistochemical analysis of c-MYC expression (no hematoxylin counterstain) in the intestinal epithelium at 70 hr post-IRR and the enumeration of nuclear c-MYC+ cells per crypt at 70 hr post-IRR (mean ± SEM, ∗p < 0.05, n = 4 mice). Scale bar represents 50 μm. See also Figures S4A and S4B.
Figure 4
Figure 4
Closely Related Fzds Cannot Compensate for Fzd7 Loss (A) Fzd expression (qRT-PCR) in basal and regenerating (70 hr post-IRR) intestinal crypts of WT mice (mean ± SEM, ∗p < 0.05, n = 4 mice). (B) Fzd expression (qRT-PCR) in WT and Fzd7NLS/NLS (Fzd7KO) regenerating (70 hr post-IRR) intestinal crypts (mean ± SEM, ∗p < 0.05, n = 4 mice). (C) Lgr5 and p21 expression (qRT-PCR) in basal and regenerating (70 hr post-IRR) intestinal epithelium crypts (mean ± SEM, ∗p < 0.05, n = 4 mice). (D) Immunohistochemical analysis of P21 expression in WT and Fzd7NLS/NLS (Fzd7KO) regenerating (70 hr post-IRR) intestinal crypts. Brackets indicate crypt domain and the enumeration of P21+ cells per crypt at 70 hr post-IRR (mean ± SEM, ∗p < 0.05, n = 4 mice). Scale bar represents 50 μm. (E) Immunoblot (IB) of FLAG immunoprecipitates (IP) from HEK293T cells transfected with the indicated expression plasmids. See also Figure S4C.
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