Biology subjects

Roelink, H.

Publications and source records attributed to Roelink, H..

3 recordsLinked to original sources

bioRxiv2018

Loss of the Heparan Sulfate Proteoglycan Glypican5 facilitates long range Shh signaling.

As a morphogen, Sonic Hedgehog (Shh) mediates signaling at a distance from its sites of synthesis. After secretion, Shh must traverse a distance through the extracellular matrix (ECM) to reach the target cells and activate the Hh response. Extracellular matrix proteins, in particular the Heparan Sulfate Proteoglycans (HSPGs) of the Glypican family have both negative and positive effects on non-cell autonomous Shh signaling, all attributed to their ability to bind Shh. Using mouse embryonic stem cell-derived mosaic tissues with compartments that lack the glycosyltransferases Exostosin1 (Ext1) and Exostosin2 (Ext2), or the HSPG core protein Glypican5 we show that cells surrounded by a mutated extracellular matrix are highly proficient distributing Shh. In contrast, cells that lack Ext1 function poorly secrete Shh. Our results confirm earlier observations that HSPGs can have both positive (Shh export) and negative influences (Shh distribution), and are supporting a model in which Shh presented on the cell surface in the context of HSPGs preferentially distributes into ECM that lacks HSPGs, possibly due to the absence of Shh sequestering molecules.

cell biology↗

bioRxiv2018

The Hedgehog signaling domain was acquired from a prokaryote.

Sonic Hedgehog (Shh) coordinates Zn2+ in a manner that resembles that of peptidases. The ability of Shh to undergo autoproteolytic processing is impaired in mutants that affect the Zn2+ coordination, while mutating residues essential for catalytic activity results in more stable forms of Shh. The residues involved in Zn2+ coordination in Shh are found mutated in some individuals with the congenital birth defect holoprosencephaly, demonstrating their importance in development. Highly conserved Shh domains are found a parts of some bacterial proteins that are members of the larger family of DD-peptidases, supporting the notion that Shh acts as a peptidase. Whereas this Hh/DD-peptidase motif is present in Hedgehog (Hh) proteins of nearly all animals, it is not present in Drosophila Hh, indicating that Hh signaling in fruit flies is derived, and perhaps not a good model for vertebrate Shh signaling. Sequence analysis of Hh proteins and their possible evolutionary precursors suggest that the evolution of modern Hh might have involved horizontal transfer of a bacterial gene coding of a Hh/DD-peptidase into a Cnidarian ancestor, recombining to give rise to modern Hh.

evolutionary biology↗

bioRxiv2017

ShhN-mediated activation of Smo in the absence of Ptch1/2 function

Sonic Hedgehog (Shh) signaling is characterized by strict non-cell autonomy; cells expressing Shh do not respond to their ligand. Here, we identify several Shh mutations that gain the ability to activate the Hedgehog (Hh) pathway in cis. This activation requires the extracellular cysteine rich domain of Smoothened, but is otherwise independent of Ptch1/2. Many of the identified mutations disrupt either a highly conserved catalytic motif found in peptidases or an a-helix domain frequently mutated in holoprosencephaly-causing SHH alleles. The expression of gain-of-function mutants often results in the accumulation of unprocessed Shh pro-peptide, a form of Shh we demonstrate is sufficient to activate the Hh response cell-autonomously. Our results demonstrate that Shh is capable of activating the Hh pathway via Smo independently of Ptch1/2, and that it harbors an intrinsic mechanism that prevents cell-autonomous activation of the pathway to favor non-cell autonomous signaling.

developmental biology↗