Visualization of a short-range Wnt gradient in the intestinal stem-cell niche

Abstract

Mammalian Wnt proteins are believed to act as short-range signals, yet have not been previously visualized in vivo. Self-renewal, proliferation and differentiation are coordinated along a putative Wnt gradient in the intestinal crypt. Wnt3 is produced specifically by Paneth cells. Here we have generated an epitope-tagged, functional Wnt3 knock-in allele. Wnt3 covers basolateral membranes of neighbouring stem cells. In intestinal organoids, Wnt3-transfer involves direct contact between Paneth cells and stem cells. Plasma membrane localization requires surface expression of Frizzled receptors, which in turn is regulated by the transmembrane E3 ligases Rnf43/Znrf3 and their antagonists Lgr4-5/R-spondin. By manipulating Wnt3 secretion and by arresting stem-cell proliferation, we demonstrate that Wnt3 mainly travels away from its source in a cell-bound manner through cell division, and not through diffusion. We conclude that stem-cell membranes constitute a reservoir for Wnt proteins, while Frizzled receptor turnover and 'plasma membrane dilution' through cell division shape the epithelial Wnt3 gradient.

Pituitary stem cell regulation: who is pulling the strings?

“…The pathway is composed of WNT ligands that bind to Frizzled (FZD) receptors, often in complex with low-density lipoprotein receptor-related protein (LRP), RAR-related orphan receptor (ROR) and/or protein tyrosine kinase 7 (PTK7), which all function as co-receptors (Niehrs 2012). In contrast to NOTCH ligands, WNTs are secreted although 234:3 their action remains limited to short distances (Farin et al 2016). In the absence of WNT ligand/receptor interaction, the downstream effector β-catenin is phosphorylated by a molecular complex containing the catalytic subunit glycogen synthase kinase-3β (GSK3B) and other proteins including AXIN, adenomatosis polyposis coli (APC) and casein kinase 1 (CK1) (Fig.…”

Exosomes in developmental signalling

“…This raises interesting issues because the lipid is likely to affect the trafficking, solubility and diffusion of these signalling proteins in the extracellular space. The requirement of long-range signalling by WNTs and HH has been the subject of debate (Alexandre et al, 2014;Farin et al, 2016;Serralbo and Marcelle, 2014). Nevertheless, both proteins have been shown to act over several cell diameters (Niehrs, 2010;Perrimon et al, 2012;Strigini and Cohen, 1997;Zecca et al, 1996).…”

WISP1i

“…23-25) (Farin et al 2016). These cysteine residues mediate Wnt folding and multimerization by regulating the formation of intermolecular and intramolecular disulfide bond (Janda et al 2012).…”