Thyroid hormone-regulated Wnt5a/Ror2 signaling is essential for dedifferentiation of larval epithelial cells into adult stem cells in the Xenopus laevis intestine.

Atsuko Ishizuya-Oka,Takashi Hasebe,Mitsuko Kajita,Masaru Katoh

doi:10.1371/journal.pone.0107611

Abstract

Background and AimsAmphibian intestinal remodeling, where thyroid hormone (T3) induces some larval epithelial cells to become adult stem cells analogous to the mammalian intestinal ones, serves as a unique model for studying how the adult stem cells are formed. To clarify its molecular mechanisms, we here investigated roles of non-canonical Wnt signaling in the larval-to-adult intestinal remodeling during Xenopus laevis metamorphosis.Methods/FindingsOur quantitative RT-PCR (qRT-PCR) and immunohistochemical analyses indicated that the expressions of Wnt5a and its receptors, frizzled 2 (Fzd2) and receptor tyrosine kinase-like orphan receptor 2 (Ror2) are up-regulated by T3 and are spatiotemporally correlated with adult epithelial development in the X. laevis intestine. Notably, changes in morphology of larval absorptive epithelial cells expressing Ror2 coincide well with formation of the adult stem cells during metamorphosis. In addition, by using organ cultures of the tadpole intestine, we have experimentally shown that addition of exogenous Wnt5a protein to the culture medium causes morphological changes in the larval epithelium expressing Ror2 even in the absence of T3. In contrast, in the presence of T3 where the adult stem cells are formed in vitro, inhibition of endogenous Wnt5a by an anti-Wnt5a antibody suppressed the epithelial morphological changes, leading to the failure of stem cell formation.SignificanceOur findings strongly suggest that the adult stem cells originate from the larval absorptive cells expressing Ror2, which require Wnt5a/Ror2 signaling for their dedifferentiation accompanied by changes in cell morphology.

Highlights

Adult organ-specific stem cells play critical roles in homeostasis and regeneration of vertebrate organs throughout adulthood
To determine the temporal relationship between the expression of Wnt5a, frizzled 2 (Fzd2), and receptor 2 (Ror2) mRNAs and the larval-to-adult intestinal remodeling, we first examined their expression in the X. laevis small intestine during natural metamorphosis by quantitative RT-PCR (qRT-PCR)
Our tissue recombinant experiments indicated that the adult stem cells are derived from the differentiated larval epithelium of the tadpole intestine before metamorphosis [26]

Summary

Introduction

Adult organ-specific stem cells play critical roles in homeostasis and regeneration of vertebrate organs throughout adulthood. A growing body of evidence indicates important roles of canonical Wnt and Notch signaling pathways in maintenance of the stem cells in the adult mammalian intestine [1,2] It still remains poorly understood how the adult stem cells and their niche are formed during postembryonic development in any vertebrate. Increasing evidence indicates that mammalian intestinal stem cell markers such as Musashi-1 (Msi1) [12,13] and leucine-rich repeat-containing G proteincoupled receptor 5 (Lgr5) [14,15,16] are expressed in the islets of X. laevis intestine at and after stage 60 [17,18] This amphibian model offers a valuable opportunity to understand how the adult stem cells and their niche are formed during normal development. To clarify its molecular mechanisms, we here investigated roles of non-canonical Wnt signaling in the larval-to-adult intestinal remodeling during Xenopus laevis metamorphosis

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Results

Conclusion