Cytoneme delivery of sonic hedgehog from ligand-producing cells requires Myosin 10 and a dispatched-BOC/CDON co-receptor complex

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.

Myosin 10 and a Cytoneme-Localized Ligand Complex Promote Morphogen Transport

SummaryMorphogens function in concentration-dependent manners to instruct cell fate during tissue patterning. Molecular mechanisms by which these signaling gradients are established and reinforced remain enigmatic. The cytoneme transport model posits that specialized filopodia extend between morphogen-sending and responding cells to ensure that appropriate signal activation thresholds are achieved across developing tissues. How morphogens are transported along and deployed from cytonemes is not known. Herein we show that the actin motor Myosin 10 promotes cytoneme-based transport of Sonic Hedgehog (SHH) morphogen to filopodial tips, and that SHH movement within cytonemes occurs by vesicular transport. We demonstrate that cytoneme-mediated deposition of SHH onto receiving cells induces a rapid signal response, and that SHH cytonemes are promoted by a complex containing a ligand-specific deployment protein and associated co-receptor.One-Sentence summaryCytoneme-based delivery of the Sonic Hedgehog activation signal is promoted by Myosin 10 and BOC/CDON co-receptor function.

Local accumulation times of morphogen gradient with tissue growth

During development of multicellular organisms, morphogen is a kind of signaling molecules produced at a local region and transported into a development field, which acts as dose-dependent regulators of gene expression, directs and controls cellular differentiation. Some experiments showed that during embryo development, dynamical processes of morphogen transport always accompany the tissue growth. However, how tissue growth affects morphogen gradients remains to be explored. To answer this problem, we propose a reaction-diffusion-convection model for morphogen transport. For this model, we mainly investigate local accumulation times (LATs) of morphogen gradients, which are a measure for time of forming the steady state of morphogen gradients. In this paper, we simplify the method of calculating the LATs and use this method to obtain analytic expressions of the LATs for uniform and linear growth, respectively. Besides, for tissue nonuniform growth, we apply an approximation method of the LATs to study them. This paper shows that tissue growth can shorten the LATs of morphogen gradients.

Extracellular Vesicle-delivered Bone Morphogenetic Proteins: A novel paracrine mechanism during embryonic development

Morphogens including Wnt, Hedgehog and BMP proteins are essential during embryonic development and early induction of organ progenitors. Besides free diffusion to form signalling gradients, extracellular vesicle- (EV-) mediated morphogen transport was identified as a central mechanism for Wnt- and Hh-signalling. Here, we investigated EVs isolated from whole zebrafish embryos as a potential morphogen transport mechanism. Inhibition of EV-secretion during development leads to severe dorsalization phenotypes, reminiscent of disrupted BMP-signalling. Subsequently, we found that EVs isolated from zebrafish embryos at bud stage contain biologically active BMP2/4 protein. Embryos with inhibited EV secretion display reduced Smad1/5/9-phosphorylation and downstream gene expression activity. We further show that BMP-containing EVs are secreted by endodermal cells in vitro, and inhibition of endodermal-EV release in vivo causes signs of BMP signalling loss. Our data provides evidence that establishes the transport of BMP2/4 by EVs as an essential but so far undiscovered mechanism in developmental morphogenesis.

Proteolytic processing of palmitoylated Hedgehog peptides specifies the 3-4 intervein region of the Drosophila wing

Cell fate determination during development often requires morphogen transport from producing to distant responding cells. Hedgehog (Hh) morphogens present a challenge to this concept, as all Hhs are synthesized as terminally lipidated molecules that form insoluble clusters at the surface of producing cells. While several proposed Hh transport modes tie directly into these unusual properties, the crucial step of Hh relay from producing cells to receptors on remote responding cells remains unresolved. Using wing development in Drosophila melanogaster as a model, we show that Hh relay and direct patterning of the 3–4 intervein region strictly depend on proteolytic removal of lipidated N-terminal membrane anchors. Site-directed modification of the N-terminal Hh processing site selectively eliminated the entire 3–4 intervein region, and additional targeted removal of N-palmitate restored its formation. Hence, palmitoylated membrane anchors restrict morphogen spread until site-specific processing switches membrane-bound Hh into bioactive forms with specific patterning functions.