Cytoneme delivery of Sonic Hedgehog from ligand-producing cells requires Myosin 10 and a Dispatched-BOC/CDON co-receptor complex

Abstract

Morphogens function in concentration-dependent manners to instruct cell fate during tissue patterning. The cytoneme morphogen transport model posits that specialized filopodia extend between morphogen-sending and responding cells to ensure that appropriate signaling thresholds are achieved. How morphogens are transported along and deployed from cytonemes, how quickly a cytoneme-delivered, receptor-dependent signal is initiated, and whether these processes are conserved across phyla are not known. Herein, we reveal that the actin motor Myosin 10 promotes vesicular transport of Sonic Hedgehog (SHH) morphogen in mouse cell cytonemes, and that SHH morphogen gradient organization is altered in neural tubes of Myo10-/- mice. We demonstrate that cytoneme-mediated deposition of SHH onto receiving cells induces a rapid, receptor-dependent signal response that occurs within seconds of ligand delivery. This activity is dependent upon a novel Dispatched (DISP)-BOC/CDON co-receptor complex that functions in ligand-producing cells to promote cytoneme occurrence and facilitate ligand delivery for signal activation.

Dispatching plasma membrane cholesterol and Sonic Hedgehog dispatch: two sides of the same coin?

“…HS consists of negatively charged sugar chains at the cell surface with different degrees of sulfation [62]. HS-dependent Hh transport was previously explained by unspecific electrostatic binding of Hh/lipophorin complexes to HS as a prerequisite for subsequent Hh binding to Ptc [63] orrather indirectlyby HS-dependent guidance and growth of long, specialized cytonemes that connect Hh-producing and receiving cells in vitro [5] and in vivo [64][65][66]. Of note, Shh co-localizes with Disp in cytonemes [5], and Hh reception takes place in membrane contact sites between Hh-sending cytonemes and Ptc-receptors on Hh-receiving cytonemes [65].…”

“…In Drosophila and in mammalian systems, Hhs are then solubilized from these platforms and travel to target cells at a significant distance from the source (∼300 mm in vertebrates and ∼50 mm in the fly) in order to bind to their receptor Patched (Ptc, also known as Ptch1). Possible mechanisms for Hh release and relay include Hh transport with lipoprotein particles [4], long-range transport via thin cellular extensions called cytonemes [5] and association of the vertebrate Hh family member Sonic Hh (Shh) with the soluble glycoprotein Scube2 (Signal sequence, cubulin (CUB) domain, epidermal-growth-factor (EGF)-like protein 2) [6][7][8]. Another possible means of releasing biologically active Shh from the plasma membrane is proteolytic Hh morphogen processing from its lipidated peptide terminia process called sheddingas demonstrated in vitro [9,10] and in vivo [11,12].…”

Reciprocal regulation of Shh trafficking and H2O2 levels via a noncanonical BOC-Rac1 pathway

“…Shh can be delivered to the receiving cells via filopodia, and it has been proposed that the length of filopodia impacts Shh distribution (Fairchild and Barna, 2014;Gonzalez-Mendez et al, 2019;Gradilla et al, 2018;Hall et al, 2019;Hall et al, 2021;Kornberg and Roy, 2014;Sanders et al, 2013). We used a double-transgenic fish 2.4Shha-ABC:Gal4FF; Shh-mChe<UAS>GFP-farn with bidirectional UAS-driven expression to visualize both Shh and plasma membranes in the MFP.…”

“…As thoroughly discussed in Acevedo and Gonzalez-Billault (Acevedo and Gonzalez-Billault, 2018), this leads to NOX2 activation along the redox branch of Rac1 activity and membrane protrusion growth along the actin cytoskeleton branch. Very recently, Shh cytoneme formation in rodent cells was demonstrated to depend on another feedback loop, including a Disp-BOC co-receptor complex (Hall et al, 2021).…”

“…Signaling filopodia or cytonemes are a common route for the secretion of morphogens (Gradilla et al, 2018;Ramirez-Weber and Kornberg, 1999) and it was recently shown that several morphogens (Fgf2, Wnt8a, Wnt3a, Shh) are involved in a regulatory loop with cytoneme formation and growth, independent of their canonical pathway (Hall et al, 2021;Mattes et al, 2018). This happens during embryonic development, at a time when H2O2 levels are highly dynamic (Rampon et al, 2018).…”