Glypicans define unique roles for the Hedgehog co-receptors boi and ihog in cytoneme-mediated gradient formation

Eléanor Simon,Adrián Aguirre-Tamaral,Pedro Ripoll,David Sánchez-Hernández,Laura González-Méndez,Gustavo Aguilar,Isabel Guerrero,Carlos Jiménez-Jiménez,Irene Seijo-Barandiarán

doi:10.7554/elife.64581

Abstract

The conserved family of Hedgehog (Hh) signaling proteins plays a key role in cell-cell communication in development, tissue repair, and cancer progression, inducing distinct concentration-dependent responses in target cells located at short and long distances. One simple mechanism for long distance dispersal of the lipid modified Hh is the direct contact between cell membranes through filopodia-like structures known as cytonemes. Here we have analyzed in Drosophila the interaction between the glypicans Dally and Dally-like protein, necessary for Hh signaling, and the adhesion molecules and Hh coreceptors Ihog and Boi. We describe that glypicans are required to maintain the levels of Ihog, but not of Boi. We also show that the overexpression of Ihog, but not of Boi, regulates cytoneme dynamics through their interaction with glypicans, the Ihog fibronectin III domains being essential for this interaction. Our data suggest that the regulation of glypicans over Hh signaling is specifically given by their interaction with Ihog in cytonemes. Contrary to previous data, we also show that there is no redundancy of Ihog and Boi functions in Hh gradient formation, being Ihog, but not of Boi, essential for the long-range gradient.

Highlights

The Hedgehog (Hh) signaling pathway has a conserved central role in cell–cell communication during tissue patterning, stem cell maintenance, and cancer progression (Briscoe and Therond, 2013)
We further propose that the presence of Interference hedgehog (Ihog), but not of Brother of Ihog (Boi), in basally located cytonemes is essential for Hh signaling gradient formation
Ihog was detectable at abnormally low levels in double mutant clones for tout velu and brother of tout velu (Figure 1C); these genes code for enzymes that synthesize the heparan sulfate (HS)-GAG chains of the glypican core proteins Dally and Dally-like protein (Dlp) (Takei et al, 2004; Han et al, 2004)

Summary

Introduction

The Hedgehog (Hh) signaling pathway has a conserved central role in cell–cell communication during tissue patterning, stem cell maintenance, and cancer progression (Briscoe and Therond, 2013). To activate its targets in a concentrationdependent manner, Hh binds to its receptor complex formed by the canonical receptor Patched (Ptc), the co-receptors Interference hedgehog (Ihog) and Brother of Ihog (Boi) (Yao et al, 2006b), and the membrane-anchored glypicans Dally-like protein (Dlp) and Dally (Desbordes and Sanson, 2003; Lum et al, 2003b; Han et al, 2004; Williams et al, 2010) All these proteins are associated with Hh presenting (Bilioni et al, 2013; Bischoff et al, 2013) and receiving cytonemes (Chen et al, 2017; Gonzalez-Mendez et al, 2017). We further propose that the presence of Ihog, but not of Boi, in basally located cytonemes is essential for Hh signaling gradient formation

Results

Discussion

Materials and methods