1
|
Waas B, Carpenter BS, Franks NE, Merchant OQ, Verhey KJ, Allen BL. Dual and opposing roles for the kinesin-2 motor, KIF17, in Hedgehog-dependent cerebellar development. SCIENCE ADVANCES 2024; 10:eade1650. [PMID: 38669326 PMCID: PMC11051677 DOI: 10.1126/sciadv.ade1650] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Accepted: 03/26/2024] [Indexed: 04/28/2024]
Abstract
While the kinesin-2 motors KIF3A and KIF3B have essential roles in ciliogenesis and Hedgehog (HH) signal transduction, potential role(s) for another kinesin-2 motor, KIF17, in HH signaling have yet to be explored. Here, we investigated the contribution of KIF17 to HH-dependent cerebellar development, where Kif17 is expressed in both HH-producing Purkinje cells and HH-responding cerebellar granule neuron progenitors (CGNPs). Germline Kif17 deletion in mice results in cerebellar hypoplasia due to reduced CGNP proliferation, a consequence of decreased HH pathway activity mediated through decreased Sonic HH (SHH) protein. Notably, Purkinje cell-specific Kif17 deletion partially phenocopies Kif17 germline mutants. Unexpectedly, CGNP-specific Kif17 deletion results in the opposite phenotype-increased CGNP proliferation and HH target gene expression due to altered GLI transcription factor processing. Together, these data identify KIF17 as a key regulator of HH-dependent cerebellar development, with dual and opposing roles in HH-producing Purkinje cells and HH-responding CGNPs.
Collapse
Affiliation(s)
- Bridget Waas
- Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Brandon S. Carpenter
- Department of Molecular and Cellular Biology, College of Science and Mathematics, Kennesaw State University, Kennesaw, GA, 30061, USA
| | - Nicole E. Franks
- Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Olivia Q. Merchant
- Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Kristen J. Verhey
- Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Benjamin L. Allen
- Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, MI, 48109, USA
| |
Collapse
|
2
|
Bostock MP, Prasad AR, Donoghue A, Fernandes VM. Photoreceptors generate neuronal diversity in their target field through a Hedgehog morphogen gradient in Drosophila. eLife 2022; 11:78093. [PMID: 36004721 PMCID: PMC9507128 DOI: 10.7554/elife.78093] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Accepted: 08/23/2022] [Indexed: 11/13/2022] Open
Abstract
Defining the origin of neuronal diversity is a major challenge in developmental neurobiology. The Drosophila visual system is an excellent paradigm to study how cellular diversity is generated. Photoreceptors from the eye disc grow their axons into the optic lobe and secrete Hedgehog (Hh) to induce the lamina, such that for every unit eye there is a corresponding lamina unit made up of post-mitotic precursors stacked into columns. Each differentiated column contains five lamina neuron types (L1-L5), making it the simplest neuropil in the optic lobe, yet how this diversity is generated was unknown. Here, we found that Hh pathway activity is graded along the distal-proximal axis of lamina columns and further determined that this gradient in pathway activity arises from a gradient of Hh ligand. We manipulated Hh pathway activity cell-autonomously in lamina precursors and non-cell autonomously by inactivating the Hh ligand, and by knocking it down in photoreceptors. These manipulations showed that different thresholds of activity specify unique cell identities, with more proximal cell types specified in response to progressively lower Hh levels. Thus, our data establish that Hh acts as a morphogen to pattern the lamina. Although, this is the first such report during Drosophila nervous system development, our work uncovers a remarkable similarity with the vertebrate neural tube, which is patterned by Sonic Hedgehog. Altogether, we show that differentiating neurons can regulate the neuronal diversity of their distant target fields through morphogen gradients.
Collapse
Affiliation(s)
- Matthew P Bostock
- Department of Cell and Developmental Biology, University College London, London, United Kingdom
| | - Anadika R Prasad
- Department of Cell and Developmental Biology, University College London, London, United Kingdom
| | - Alicia Donoghue
- Department of Cell and Developmental Biology, University College London, London, United Kingdom
| | - Vilaiwan M Fernandes
- Department of Cell and Developmental Biology, University College London, London, United Kingdom
| |
Collapse
|
3
|
Pizette S, Matusek T, Herpers B, Thérond PP, Rabouille C. Hherisomes, Hedgehog specialized recycling endosomes, are required for high level Hedgehog signaling and tissue growth. J Cell Sci 2021; 134:268340. [PMID: 34028543 DOI: 10.1242/jcs.258603] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Accepted: 04/07/2021] [Indexed: 01/03/2023] Open
Abstract
In metazoans, tissue growth and patterning is partly controlled by the Hedgehog (Hh) morphogen. Using immuno-electron microscopy on Drosophila wing imaginal discs, we identified a cellular structure, the Hherisomes, which contain the majority of intracellular Hh. Hherisomes are recycling tubular endosomes, and their formation is specifically boosted by overexpression of Hh. Expression of Rab11, a small GTPase involved in recycling endosomes, boosts the size of Hherisomes and their Hh concentration. Conversely, increased expression of the transporter Dispatched, a regulator of Hh secretion, leads to their clearance. We show that increasing Hh density in Hherisomes through Rab11 overexpression enhances both the level of Hh signaling and disc pouch growth, whereas Dispatched overexpression decreases high-level Hh signaling and growth. We propose that, upon secretion, a pool of Hh triggers low-level signaling, whereas a second pool of Hh is endocytosed and recycled through Hherisomes to stimulate high-level signaling and disc pouch growth. Altogether, our data indicate that Hherisomes are required to sustain physiological Hh activity necessary for patterning and tissue growth in the wing disc.
Collapse
Affiliation(s)
- Sandrine Pizette
- Université Côte d'Azur, Centre National de la Recherche Scientifique (CNRS), Inserm, Institute of Biology-Valrose (iBV), 06108 Nice Cedex 2, France
| | - Tamás Matusek
- Université Côte d'Azur, Centre National de la Recherche Scientifique (CNRS), Inserm, Institute of Biology-Valrose (iBV), 06108 Nice Cedex 2, France
| | - Bram Herpers
- Section Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, 3584 CX Utrecht, The Netherlands
| | - Pascal P Thérond
- Université Côte d'Azur, Centre National de la Recherche Scientifique (CNRS), Inserm, Institute of Biology-Valrose (iBV), 06108 Nice Cedex 2, France
| | - Catherine Rabouille
- Section Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, 3584 CX Utrecht, The Netherlands.,Hubrecht Institute/KNAW [Koninklijke Nederlandsee Akademie van Wetenschap (Dutch Royal Academy of Sciences)] and UMC Utrecht, 3584 CT Utrecht, The Netherlands.,Biological Sciences of Cells and Systems (BSBC) Department, UMC Groningen, 9713 AV Groningen, The Netherlands
| |
Collapse
|
4
|
The Elegance of Sonic Hedgehog: Emerging Novel Functions for a Classic Morphogen. J Neurosci 2019; 38:9338-9345. [PMID: 30381425 DOI: 10.1523/jneurosci.1662-18.2018] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Revised: 09/27/2018] [Accepted: 09/28/2018] [Indexed: 12/12/2022] Open
Abstract
Sonic Hedgehog (SHH) signaling has been most widely known for its role in specifying region and cell-type identity during embryonic morphogenesis. This mini-review accompanies a 2018 SFN mini-symposium that addresses an emerging body of research focused on understanding the diverse roles for Shh signaling in a wide range of contexts in neurodevelopment and, more recently, in the mature CNS. Such research shows that Shh affects the function of brain circuits, including the production and maintenance of diverse cell types and the establishment of wiring specificity. Here, we review these novel and unexpected functions and the unanswered questions regarding the role of SHH and its signaling pathway members in these cases.
Collapse
|
5
|
Rivell A, Petralia RS, Wang YX, Clawson E, Moehl K, Mattson MP, Yao PJ. Sonic hedgehog expression in the postnatal brain. Biol Open 2019; 8:bio.040592. [PMID: 30837226 PMCID: PMC6451348 DOI: 10.1242/bio.040592] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Beyond its role in patterning the neural tube during embryogenesis, additional functions of Sonic hedgehog (Shh) in post-embryonic and mature brains have been coming into focus. However, the question of the abundance of endogenous Shh - the ligand of the signaling pathway - and its changes over time in post-embryonic and mature brains are less well understood. Here we find that while the amounts of Shh transcript and protein in rat brains are nearly undetectable at birth, they increase continuously during postnatal development and remain at readily detectable levels in young adults. This developmental age-associated increase in Shh levels is also seen in hippocampal neurons grown in culture, in which very young neurons produce minimal amounts of Shh protein but, as neurons grow and form synapses, the amounts of Shh increase significantly. Using immunolabeling with antibodies to different residues of Shh, we observed that the N-terminal fragment and the C-terminal fragment of Shh are present in hippocampal neurons, and that these two Shh forms co-exist in most compartments of the neuron. Our findings provide a better understanding of Shh expression in the brain, laying the groundwork for further comprehending the biogenesis of Shh protein in the young and mature brain and neurons.
Collapse
Affiliation(s)
- Aileen Rivell
- Laboratory of Neurosciences, NIA/NIH, Baltimore, MD 21224, USA
| | | | - Ya-Xian Wang
- Advanced Imaging Core, NIDCD/NIH, Bethesda, MD 20892, USA
| | - Ellie Clawson
- Laboratory of Neurosciences, NIA/NIH, Baltimore, MD 21224, USA
| | - Keelin Moehl
- Laboratory of Neurosciences, NIA/NIH, Baltimore, MD 21224, USA
| | - Mark P Mattson
- Laboratory of Neurosciences, NIA/NIH, Baltimore, MD 21224, USA.,Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Pamela J Yao
- Laboratory of Neurosciences, NIA/NIH, Baltimore, MD 21224, USA
| |
Collapse
|
6
|
Sohr A, Du L, Wang R, Lin L, Roy S. Drosophila FGF cleavage is required for efficient intracellular sorting and intercellular dispersal. J Cell Biol 2019; 218:1653-1669. [PMID: 30808704 PMCID: PMC6504889 DOI: 10.1083/jcb.201810138] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Revised: 01/30/2019] [Accepted: 02/05/2019] [Indexed: 01/15/2023] Open
Abstract
Bnl controls tracheal development in Drosophila, but it is unclear how this fibroblast growth factor is prepared for tissue-specific dispersal. Sohr et al. find that Furin1 cleaves Bnl in the Golgi, which polarizes its sorting to the basal surface of the source cells and determines its range of cytoneme-mediated intercellular dispersion, signaling, and branching morphogenesis. How morphogenetic signals are prepared for intercellular dispersal and signaling is fundamental to the understanding of tissue morphogenesis. We discovered an intracellular mechanism that prepares Drosophila melanogaster FGF Branchless (Bnl) for cytoneme-mediated intercellular dispersal during the development of the larval Air-Sac-Primordium (ASP). Wing-disc cells express Bnl as a proprotein that is cleaved by Furin1 in the Golgi. Truncated Bnl sorts asymmetrically to the basal surface, where it is received by cytonemes that extend from the recipient ASP cells. Uncleavable mutant Bnl has signaling activity but is mistargeted to the apical side, reducing its bioavailability. Since Bnl signaling levels feedback control cytoneme production in the ASP, the reduced availability of mutant Bnl on the source basal surface decreases ASP cytoneme numbers, leading to a reduced range of signal/signaling gradient and impaired ASP growth. Thus, enzymatic cleavage ensures polarized intracellular sorting and availability of Bnl to its signaling site, thereby determining its tissue-specific intercellular dispersal and signaling range.
Collapse
Affiliation(s)
- Alex Sohr
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD
| | - Lijuan Du
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD
| | - Ruofan Wang
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD
| | - Li Lin
- Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA
| | - Sougata Roy
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD
| |
Collapse
|
7
|
Daniele JR, Baqri RM, Kunes S. Analysis of axonal trafficking via a novel live-imaging technique reveals distinct hedgehog transport kinetics. Biol Open 2017; 6:714-721. [PMID: 28298319 PMCID: PMC5450320 DOI: 10.1242/bio.024075] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The Drosophila melanogaster (Dmel) eye is an ideal model to study development, intracellular signaling, behavior, and neurodegenerative disease. Interestingly, dynamic data are not commonly employed to investigate eye-specific disease models. Using axonal transport of the morphogen Hedgehog (Hh), which is integral to Dmel eye-brain development and implicated in stem cell maintenance and neoplastic disease, we demonstrate the ability to comprehensively quantify and characterize its trafficking in various neuron types and a neurodegeneration model in live early third-instar larval Drosophila. We find that neuronal Hh, whose kinetics have not been reported previously, favors fast anterograde transport and varies in speed and flux with respect to axonal position. This suggests distinct trafficking pathways along the axon. Lastly, we report abnormal transport of Hh in an accepted model of photoreceptor neurodegeneration. As a technical complement to existing eye-specific disease models, we demonstrate the ability to directly visualize transport in real time in intact and live animals and track secreted cargoes from the axon to their release points. Particle dynamics can now be precisely calculated and we posit that this method could be conveniently applied to characterizing disease pathogenesis and genetic screening in other established models of neurodegeneration. Summary: A novel method to directly visualize Hedgehog transport in the photoreceptor neurons of living animals offers unprecedented positional and temporal detail of complex phenotypes in real time.
Collapse
Affiliation(s)
- Joseph R Daniele
- Department of Molecular & Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA
| | - Rehan M Baqri
- Department of Molecular & Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA
| | - Sam Kunes
- Department of Molecular & Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA
| |
Collapse
|
8
|
Daniele JR, Chu T, Kunes S. A novel proteolytic event controls Hedgehog intracellular sorting and distribution to receptive fields. Biol Open 2017; 6:540-550. [PMID: 28298318 PMCID: PMC5450321 DOI: 10.1242/bio.024083] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The patterning activity of a morphogen depends on secretion and dispersal mechanisms that shape its distribution to the cells of a receptive field. In the case of the protein Hedgehog (Hh), these mechanisms of secretion and transmission remain unclear. In the developing Drosophila visual system, Hh is partitioned for release at opposite poles of photoreceptor neurons. Release into the retina regulates the progression of eye development; axon transport and release at axon termini trigger the development of postsynaptic neurons in the brain. Here we show that this binary targeting decision is controlled by a C-terminal proteolysis. Hh with an intact C-terminus undergoes axonal transport, whereas a C-terminal proteolysis enables Hh to remain in the retina, creating a balance between eye and brain development. Thus, we define a novel mechanism for the apical/basal targeting of this developmentally important protein and posit that similar post-translational regulation could underlie the polarity of related ligands.
Collapse
Affiliation(s)
- Joseph R Daniele
- Department of Molecular & Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA
| | - Tehyen Chu
- Department of Molecular & Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA
| | - Sam Kunes
- Department of Molecular & Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA
| |
Collapse
|
9
|
The Many Hats of Sonic Hedgehog Signaling in Nervous System Development and Disease. J Dev Biol 2016; 4:jdb4040035. [PMID: 29615598 PMCID: PMC5831807 DOI: 10.3390/jdb4040035] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Revised: 11/17/2016] [Accepted: 11/29/2016] [Indexed: 02/06/2023] Open
Abstract
Sonic hedgehog (Shh) signaling occurs concurrently with the many processes that constitute nervous system development. Although Shh is mostly known for its proliferative and morphogenic action through its effects on neural stem cells and progenitors, it also contributes to neuronal differentiation, axonal pathfinding and synapse formation and function. To participate in these diverse events, Shh signaling manifests differently depending on the maturational state of the responsive cell, on the other signaling pathways regulating neural cell function and the environmental cues that surround target cells. Shh signaling is particularly dynamic in the nervous system, ranging from canonical transcription-dependent, to non-canonical and localized to axonal growth cones. Here, we review the variety of Shh functions in the developing nervous system and their consequences for neurodevelopmental diseases and neural regeneration, with particular emphasis on the signaling mechanisms underlying Shh action.
Collapse
|
10
|
Abstract
UNLABELLED The presence of Sonic Hedgehog (Shh) and its signaling components in the neurons of the hippocampus raises a question about what role the Shh signaling pathway may play in these neurons. We show here that activation of the Shh signaling pathway stimulates axon elongation in rat hippocampal neurons. This Shh-induced effect depends on the pathway transducer Smoothened (Smo) and the transcription factor Gli1. The axon itself does not respond directly to Shh; instead, the Shh signal transduction originates from the somatodendritic region of the neurons and occurs in neurons with and without detectable primary cilia. Upon Shh stimulation, Smo localization to dendrites increases significantly. Shh pathway activation results in increased levels of profilin1 (Pfn1), an actin-binding protein. Mutations in Pfn1's actin-binding sites or reduction of Pfn1 eliminate the Shh-induced axon elongation. These findings indicate that Shh can regulate axon growth, which may be critical for development of hippocampal neurons. SIGNIFICANCE STATEMENT Although numerous signaling mechanisms have been identified that act directly on axons to regulate their outgrowth, it is not known whether signals transduced in dendrites may also affect axon outgrowth. We describe here a transcellular signaling pathway in embryonic hippocampal neurons in which activation of Sonic Hedgehog (Shh) receptors in dendrites stimulates axon growth. The pathway involves the dendritic-membrane-associated Shh signal transducer Smoothened (Smo) and the transcription factor Gli, which induces the expression of the gene encoding the actin-binding protein profilin 1. Our findings suggest scenarios in which stimulation of Shh in dendrites results in accelerated outgrowth of the axon, which therefore reaches its presumptive postsynaptic target cell more quickly. By this mechanism, Shh may play critical roles in the development of hippocampal neuronal circuits.
Collapse
|
11
|
D'Angelo G, Matusek T, Pizette S, Thérond PP. Endocytosis of Hedgehog through dispatched regulates long-range signaling. Dev Cell 2015; 32:290-303. [PMID: 25619925 DOI: 10.1016/j.devcel.2014.12.004] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Revised: 09/22/2014] [Accepted: 12/01/2014] [Indexed: 01/20/2023]
Abstract
The proteins of the Hedgehog (Hh) family are secreted proteins exerting short- and long-range control over various cell fates in developmental patterning. The Hh gradient in Drosophila wing imaginal discs consists of apical and basolateral secreted pools, but the mechanisms governing the overall establishment of the gradient remain unclear. We investigated the relative contributions of endocytosis and recycling to control the Hh gradient. We show that, upon its initial apical secretion, Hh is re-internalized. We examined the effect of the resistance-nodulation-division transporter Dispatched (Disp) on long-range Hh signaling and unexpectedly found that Disp is specifically required for apical endocytosis of Hh. Re-internalized Hh is then regulated in a Rab5- and Rab4-dependent manner to ensure its long-range activity. We propose that Hh-producing cells integrate endocytosis and recycling as two instrumental mechanisms contributing to regulate the long-range activity of Hh.
Collapse
Affiliation(s)
- Gisela D'Angelo
- Institut de Biologie de Valrose - iBV, Centre de Biochimie, Université Nice Sophia Antipolis, CNRS UMR7277, INSERM 1091, Parc Valrose, 06108 Nice Cedex 2, France.
| | - Tamás Matusek
- Institut de Biologie de Valrose - iBV, Centre de Biochimie, Université Nice Sophia Antipolis, CNRS UMR7277, INSERM 1091, Parc Valrose, 06108 Nice Cedex 2, France
| | - Sandrine Pizette
- Institut de Biologie de Valrose - iBV, Centre de Biochimie, Université Nice Sophia Antipolis, CNRS UMR7277, INSERM 1091, Parc Valrose, 06108 Nice Cedex 2, France
| | - Pascal P Thérond
- Institut de Biologie de Valrose - iBV, Centre de Biochimie, Université Nice Sophia Antipolis, CNRS UMR7277, INSERM 1091, Parc Valrose, 06108 Nice Cedex 2, France.
| |
Collapse
|
12
|
Kornberg TB. Cytonemes and the dispersion of morphogens. WILEY INTERDISCIPLINARY REVIEWS. DEVELOPMENTAL BIOLOGY 2014; 3:445-63. [PMID: 25186102 PMCID: PMC4199865 DOI: 10.1002/wdev.151] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2014] [Revised: 07/10/2014] [Accepted: 07/25/2014] [Indexed: 01/07/2023]
Abstract
Filopodia are cellular protrusions that have been implicated in many types of mechanosensory activities. Morphogens are signaling proteins that regulate the patterned development of embryos and tissues. Both have long histories that date to the beginnings of cell and developmental biology in the early 20th century, but recent findings tie specialized filopodia called cytonemes to morphogen movement and morphogen signaling. This review explores the conceptual and experimental background for a model of paracrine signaling in which the exchange of morphogens between cells is directed to sites where cytonemes directly link cells that produce morphogens to cells that receive and respond to them.
Collapse
Affiliation(s)
- Thomas B Kornberg
- Cardiovascular Research Institute, University of California, San Francisco, CA, USA
| |
Collapse
|
13
|
Apitz H, Salecker I. A Challenge of Numbers and Diversity: Neurogenesis in theDrosophilaOptic Lobe. J Neurogenet 2014; 28:233-49. [DOI: 10.3109/01677063.2014.922558] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
|
14
|
Guerrero I, Kornberg TB. Hedgehog and its circuitous journey from producing to target cells. Semin Cell Dev Biol 2014; 33:52-62. [PMID: 24994598 DOI: 10.1016/j.semcdb.2014.06.016] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2014] [Accepted: 06/23/2014] [Indexed: 12/12/2022]
Abstract
The hedgehog (Hh) signaling protein has essential roles in the growth, development and regulation of many vertebrate and invertebrate organs. The processes that make Hh and prepare it for release from producing cells and that move it to target cells are both diverse and complex. This article reviews the essential features of these processes and highlights recent work that provides a novel framework to understand how these processes contribute to an integrated pathway.
Collapse
Affiliation(s)
- Isabel Guerrero
- Centro de Biología Molecular "Severo Ochoa" (CSIC-UAM), Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid, Spain.
| | - Thomas B Kornberg
- Cardiovascular Research Institute, University of California, San Francisco, CA 94158, USA.
| |
Collapse
|
15
|
Abstract
Development creates a vast array of forms and patterns with elegant economy, using a small vocabulary of pattern-generating proteins such as BMPs, FGFs and Hh in similar ways in many different contexts. Despite much theoretical and experimental work, the signaling mechanisms that disperse these morphogen signaling proteins remain controversial. Here, we review the conceptual background and evidence that establishes a fundamental and essential role for cytonemes as specialized filopodia that transport signaling proteins between signaling cells. This evidence suggests that cytoneme-mediated signaling is a dispersal mechanism that delivers signaling proteins directly at sites of cell-cell contact.
Collapse
Affiliation(s)
- Thomas B. Kornberg
- Cardiovascular Research Institute, University of California, San Francisco, CA 94156, USA
| | - Sougata Roy
- Cardiovascular Research Institute, University of California, San Francisco, CA 94156, USA
| |
Collapse
|
16
|
Abstract
In vivo time-lapse imaging and functional tests bring fresh evidence that the morphogen Hedgehog is conveyed to target cells via long filopodia extensions, dubbed cytonemes. This study provides the tools and conceptual framework to understand how cytonemes form and carry morphogens.
Collapse
Affiliation(s)
- James Briscoe
- MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA, UK
| | | |
Collapse
|
17
|
Gradilla AC, Guerrero I. Hedgehog on the move: a precise spatial control of Hedgehog dispersion shapes the gradient. Curr Opin Genet Dev 2013; 23:363-73. [PMID: 23747033 DOI: 10.1016/j.gde.2013.04.011] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Revised: 04/15/2013] [Accepted: 04/16/2013] [Indexed: 01/28/2023]
Abstract
Hedgehog (Hh) as morphogen directs cell differentiation during development activating various target genes in a concentration dependent manner. The mechanisms that permit controlled Hh dispersion and gradient formation remain controversial. New research in the Drosophila wing disc epithelium has revealed a crucial role of Hh recycling for its release and transportation from source cells. Lipid modifications on Hh mediate key interactions with different elements of the pathway, which balance the retention and release of the molecule through the basolateral side of the epithelium, allowing its tight spatial control. Dispersion of Hh is also determined by its hydrophobic nature, and the mechanisms that include membrane-tethered transport of Hh are increasingly proposed.
Collapse
Affiliation(s)
- Ana-Citlali Gradilla
- Centro de Biología Molecular Severo Ochoa (CSIC-UAM), C/Nicolas Cabrera 1, Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid, Spain
| | | |
Collapse
|
18
|
Briscoe J, Thérond PP. The mechanisms of Hedgehog signalling and its roles in development and disease. Nat Rev Mol Cell Biol 2013; 14:416-29. [DOI: 10.1038/nrm3598] [Citation(s) in RCA: 1338] [Impact Index Per Article: 111.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
|
19
|
Brain-specific-homeobox is required for the specification of neuronal types in the Drosophila optic lobe. Dev Biol 2013; 377:90-9. [PMID: 23454478 DOI: 10.1016/j.ydbio.2013.02.012] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Revised: 02/15/2013] [Accepted: 02/17/2013] [Indexed: 12/17/2022]
Abstract
The Drosophila optic lobe comprises a wide variety of neurons forming laminar and columnar structures similar to the mammalian brain. The Drosophila optic lobe may provide an excellent model to investigate various processes of brain development. However, it is poorly understood how neuronal specification is regulated in the optic lobe to form a complicated structure. Here we show that the Brain-specific-homeobox (Bsh) protein, which is expressed in the lamina and medulla ganglia, is involved in specifying neuronal identity. Bsh is expressed in L4 and L5 lamina neurons and in Mi1 medulla neurons. Analyses of loss-of-function and gain-of-function clones suggest that Bsh is required and largely sufficient for Mi1 specification in the medulla and L4 specification in the lamina. Additionally, Bsh is at least required for L5 specification. In the absence of Bsh, L5 is transformed into glial cells.
Collapse
|
20
|
Cytoneme-mediated cell-to-cell signaling during development. Cell Tissue Res 2013; 352:59-66. [PMID: 23435991 DOI: 10.1007/s00441-013-1578-x] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2012] [Accepted: 01/28/2013] [Indexed: 01/06/2023]
Abstract
Cell-to-cell communication is vital for animal tissues and organs to develop and function as organized units. Throughout development, intercellular communication is crucial for the generation of structural diversity, mainly by the regulation of differentiation and growth. During these processes, several signaling molecules function as messengers between cells and are transported from producing to receptor cells. Thus, a tight spatial and temporal regulation of signaling transport is likely to be critical during morphogenesis. Despite much experimental and theoretical work, the question as to how these signals move between cells remains. Cell-to-cell contact is probably the most precise spatial and temporal mechanism for the transference of signaling molecules from the producing to the receiving cells. However, most of these molecules can also function at a distance between cells that are not juxtaposed. Recent research has shown the way in which cells may achieve direct physical contact and communication through actin-based filopodia. In addition, increasing evidence is revealing the role of such filopodia in regulating spatial patterning during development; in this context, the filopodia are referred to as cytonemes. In this review, we highlight recent work concerning the roles of these filopodia in cell signaling during development. The processes that initiate and regulate the formation, orientation and dynamics of cytonemes are poorly understood but are potentially extremely important areas for our knowledge of intercellular communication.
Collapse
|
21
|
Petralia RS, Wang YX, Mattson MP, Yao PJ. Subcellular distribution of patched and smoothened in the cerebellar neurons. CEREBELLUM (LONDON, ENGLAND) 2012; 11:972-81. [PMID: 22477363 PMCID: PMC3495249 DOI: 10.1007/s12311-012-0374-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The Sonic hedgehog (Shh) signaling pathway carries out a wide range of biological functions such as patterning of the embryonic neural tube and expansion of cerebellar granule cell precursors. We previously have found that the Shh signaling receptors, Patched1 (Ptch1) and Smoothened (Smo), are expressed in hippocampal neurons of developing and adult rats, suggesting the continued presence of Shh signaling in postmitotic, differentiated neurons. Here, we report that Ptch1 and Smo are present in the processes and growth cones of immature neurons in the developing cerebellum, and that, in the mature cerebellum, Ptch1 and Smo are expressed by several types of neurons including Purkinje cells, granule cells, and interneurons. Within these neurons, Ptch1 and Smo are predominantly localized in the postsynaptic side of the synapses, a distribution pattern similar to that found in hippocampal neurons. Our findings provide morphological evidence that Shh signaling events are not confined to neuronal precursors and are likely to have ongoing roles within the postmitotic neurons of the developing and adult cerebellum.
Collapse
Affiliation(s)
| | - Ya-Xian Wang
- Advanced Imaging Core, NIDCD/NIH, Bethesda, MD 20892, USA
| | - Mark P. Mattson
- Laboratory of Neurosciences, National Institute on Aging Intramural Research Program, Baltimore, MD 21224, USA
| | - Pamela J. Yao
- Laboratory of Neurosciences, National Institute on Aging Intramural Research Program, Baltimore, MD 21224, USA. Laboratory of Neurosciences, NIA/NIH Biomedical Research Center, 251 Bayview Boulevard, Baltimore, MD 21224, USA
| |
Collapse
|
22
|
Petralia RS, Wang YX, Mattson MP, Yao PJ. Sonic hedgehog distribution within mature hippocampal neurons. Commun Integr Biol 2012; 4:775-7. [PMID: 22446553 DOI: 10.4161/cib.17832] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Sonic hedgehog (Shh) regulates neural progenitor cells in the adult brain but its role in postmitotic mature neurons is not well understood. Using immunoelectron microscopy, we have recently demonstrated the postsynaptic distribution of Patched (Ptch) and Smoothened (Smo), the receptors for Shh, in hippocampal neurons of the adult rat brain. In this study, we describe the distribution of Shh protein in these adult hippocampal neurons. We find that Shh is present in both presynaptic and postsynaptic terminals. In presynaptic terminals, Shh is located either at the center or on the side of the synaptic junction. In postsynaptic terminals, Shh is mostly located on the side of the synaptic junction. We also find Shh in dendrites. Synaptic and dendritic Shh often reside in or are associated with vesicular structures that include dense-cored vesicles, synaptic vesicles, and endosomes. Thus, our subcellular map of Shh and its receptors provides a foundation for elucidating the functional significance of Shh signaling in mature neurons.
Collapse
|
23
|
Aikin R, Cervantes A, D'Angelo G, Ruel L, Lacas-Gervais S, Schaub S, Thérond P. A genome-wide RNAi screen identifies regulators of cholesterol-modified hedgehog secretion in Drosophila. PLoS One 2012; 7:e33665. [PMID: 22432040 PMCID: PMC3303847 DOI: 10.1371/journal.pone.0033665] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2011] [Accepted: 02/14/2012] [Indexed: 12/12/2022] Open
Abstract
Hedgehog (Hh) proteins are secreted molecules that function as organizers in animal development. In addition to being palmitoylated, Hh is the only metazoan protein known to possess a covalently-linked cholesterol moiety. The absence of either modification severely disrupts the organization of numerous tissues during development. It is currently not known how lipid-modified Hh is secreted and released from producing cells. We have performed a genome-wide RNAi screen in Drosophila melanogaster cells to identify regulators of Hh secretion. We found that cholesterol-modified Hh secretion is strongly dependent on coat protein complex I (COPI) but not COPII vesicles, suggesting that cholesterol modification alters the movement of Hh through the early secretory pathway. We provide evidence that both proteolysis and cholesterol modification are necessary for the efficient trafficking of Hh through the ER and Golgi. Finally, we identified several putative regulators of protein secretion and demonstrate a role for some of these genes in Hh and Wingless (Wg) morphogen secretion in vivo. These data open new perspectives for studying how morphogen secretion is regulated, as well as provide insight into regulation of lipid-modified protein secretion.
Collapse
Affiliation(s)
- Reid Aikin
- CNRS UMR 7277, Inserm UMR 1091, Institut de Biologie Valrose (iBV), Centre de Biochimie, Nice, France
- Université de Nice-Sophia Antipolis, Nice, France
| | - Alexandra Cervantes
- CNRS UMR 7277, Inserm UMR 1091, Institut de Biologie Valrose (iBV), Centre de Biochimie, Nice, France
- Université de Nice-Sophia Antipolis, Nice, France
| | - Gisela D'Angelo
- CNRS UMR 7277, Inserm UMR 1091, Institut de Biologie Valrose (iBV), Centre de Biochimie, Nice, France
- Université de Nice-Sophia Antipolis, Nice, France
| | - Laurent Ruel
- CNRS UMR 7277, Inserm UMR 1091, Institut de Biologie Valrose (iBV), Centre de Biochimie, Nice, France
- Université de Nice-Sophia Antipolis, Nice, France
| | - Sandra Lacas-Gervais
- Centre Commun de Microscopie Appliquée (CCMA), Université de Nice-Sophia Antipolis, Nice, France
| | - Sébastien Schaub
- CNRS UMR 7277, Inserm UMR 1091, Institut de Biologie Valrose (iBV), Centre de Biochimie, Nice, France
- Université de Nice-Sophia Antipolis, Nice, France
| | - Pascal Thérond
- CNRS UMR 7277, Inserm UMR 1091, Institut de Biologie Valrose (iBV), Centre de Biochimie, Nice, France
- Université de Nice-Sophia Antipolis, Nice, France
- * E-mail:
| |
Collapse
|
24
|
Cerveny KL, Varga M, Wilson SW. Continued growth and circuit building in the anamniote visual system. Dev Neurobiol 2012; 72:328-45. [PMID: 21563317 DOI: 10.1002/dneu.20917] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Fish and amphibia are capable of lifelong growth and regeneration. The two core components of their visual system, the retina and tectum both maintain small populations of stem cells that contribute new neurons and glia to these tissues as they grow. As the animals age, the initial retinal projections onto the tectum are continuously remodeled to maintain retinotopy. These properties raise several biological challenges related to the control of proliferation and differentiation of retinal and tectal stem cells. For instance, how do stem and progenitor cells integrate intrinsic and extrinsic cues to produce the appropriate type and number of cells needed by the growing tissue. Does retinal growth or neuronal activity influence tectal growth? What are the cellular and molecular mechanisms that enable retinal axons to shift their tectal connections as these two tissues grow in incongruent patterns? While we cannot yet provide answers to these questions, this review attempts to supply background and context, laying the ground work for new investigations.
Collapse
Affiliation(s)
- Kara L Cerveny
- Department of Cell and Developmental Biology, University College, London, UK
| | | | | |
Collapse
|
25
|
Thérond PP. Release and transportation of Hedgehog molecules. Curr Opin Cell Biol 2012; 24:173-80. [PMID: 22366329 DOI: 10.1016/j.ceb.2012.02.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2011] [Revised: 01/19/2012] [Accepted: 02/05/2012] [Indexed: 10/28/2022]
Abstract
Secretion of the Hedgehog morphogen induces different cell fates over the short and long ranges during developmental patterning. Mature Hedgehog carries hydrophobic palmitic acid and cholesterol modifications essential for its correct spread. The long-range activity of Hedgehog raises questions about how a dually lipidated protein can spread in the hydrophilic environment of the extracellular space. There is compelling experimental evidence in favour of the existence of several different carriers for Hedgehog transportation, via very different routes. This suggests that different accessory proteins and cellular machineries may be involved in the specific release of Hedgehog. I suggest that Hh carriers may work in parallel within a given cell and that developmental context may condition the choice of Hh carrier in secreting cells.
Collapse
Affiliation(s)
- Pascal P Thérond
- CNRS UMR 7277, Inserm UMR 1091, Institut de Biologie Valrose - IBV, France.
| |
Collapse
|
26
|
Abstract
Hedgehog, an essential protein for the development of many vertebrate and invertebrate organs, signals at both short and long distances to control growth and patterning. The mechanism by which it moves between source and target cells is not known, but characterization of the covalent modification of its N terminus with palmitate and of its C terminus with cholesterol has led to the suggestion that the lipophilic properties of the modified protein serve to regulate movement after its secretion into the extracellular space. Another interpretation and model is that the C-terminal cholesterol acts to target Hedgehog to an intracellular trafficking pathway that prepares Hedgehog for release in an encapsulated form.
Collapse
Affiliation(s)
- Thomas B Kornberg
- Cardiovascular Research Institute, University of California, San Francisco, CA 94158, USA.
| |
Collapse
|
27
|
Yogev S, Rousso T, Schejter ED, Shilo BZ. Versatility of EGF receptor ligand processing in insects. Dev Biol 2011; 357:17-20. [DOI: 10.1016/j.ydbio.2010.12.016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2010] [Revised: 12/08/2010] [Accepted: 12/09/2010] [Indexed: 11/28/2022]
|
28
|
Beug ST, Parks RJ, McBride HM, Wallace VA. Processing-dependent trafficking of Sonic hedgehog to the regulated secretory pathway in neurons. Mol Cell Neurosci 2010; 46:583-96. [PMID: 21182949 DOI: 10.1016/j.mcn.2010.12.009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2010] [Revised: 11/25/2010] [Accepted: 12/09/2010] [Indexed: 01/22/2023] Open
Abstract
Neurons are an important source of the secreted morphogen Sonic hedgehog (Shh), however, little is known about neuron-specific regulation of Shh transport and secretion. To study this process, we investigated the subcellular distribution of Shh in primary neurons and differentiated cells of a neuroendocrine cell line by fluorescence microscopy and biochemical fractionation. In retinal ganglion cells, endogenous Shh was distributed as intra- and extracellular puncta at the soma, dendrites, axons and neurite terminals. Shh(+) puncta move bidirectionally and colocalize with markers of synaptic vesicles (SVs) and dense core granules. Lipid modification and proteolysis were required for Shh sorting to SVs and cell surface association. Finally, consistent with its association with regulated secretory vesicles, Shh secretion could be induced under depolarizing conditions. Taken together, these observations suggest that long-range Shh transport and signalling in neurons involves trafficking to the regulated secretory pathway and cell surface accumulation of Shh on axons and suggests a link between neuronal activity and Shh release.
Collapse
Affiliation(s)
- Shawn T Beug
- Vision Program, Ottawa Hospital Research Institute, 501 Smyth Road, Ottawa, Ontario, Canada
| | | | | | | |
Collapse
|
29
|
Yogev S, Schejter ED, Shilo BZ. Polarized secretion of Drosophila EGFR ligand from photoreceptor neurons is controlled by ER localization of the ligand-processing machinery. PLoS Biol 2010; 8. [PMID: 20957186 PMCID: PMC2950126 DOI: 10.1371/journal.pbio.1000505] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2010] [Accepted: 08/23/2010] [Indexed: 11/18/2022] Open
Abstract
The release of signaling molecules from neurons must be regulated, to accommodate their highly polarized structure. In the developing Drosophila visual system, photoreceptor neurons secrete the epidermal growth factor receptor ligand Spitz (Spi) from their cell bodies, as well as from their axonal termini. Here we show that subcellular localization of Rhomboid proteases, which process Spi, determines the site of Spi release from neurons. Endoplasmic reticulum (ER) localization of Rhomboid 3 is essential for its ability to promote Spi secretion from axons, but not from cell bodies. We demonstrate that the ER extends throughout photoreceptor axons, and show that this feature facilitates the trafficking of the Spi precursor, the ligand chaperone Star, and Rhomboid 3 to axonal termini. Following this trafficking step, secretion from the axons is regulated in a manner similar to secretion from cell bodies. These findings uncover a role for the ER in trafficking proteins from the neuronal cell body to axon terminus.
Collapse
Affiliation(s)
- Shaul Yogev
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Eyal D. Schejter
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Ben-Zion Shilo
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
- * E-mail:
| |
Collapse
|
30
|
Planarian Hedgehog/Patched establishes anterior-posterior polarity by regulating Wnt signaling. Proc Natl Acad Sci U S A 2009; 106:22329-34. [PMID: 20018728 DOI: 10.1073/pnas.0907464106] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Despite long-standing interest, the molecular mechanisms underlying the establishment of anterior-posterior (AP) polarity remain among the unsolved mysteries in metazoans. In the planarians (a family of flatworms), canonical Wnt/beta-catenin signaling is required for posterior specification, as it is in many animals. However, the molecular mechanisms regulating the posterior-specific induction of Wnt genes according to the AP polarity have remained unclear. Here, we demonstrate that Hedgehog (Hh) signaling is responsible for the establishment of AP polarity via its regulation of the transcription of Wnt family genes during planarian regeneration. We found that RNAi gene knockdown of Dugesia japonica patched (Djptc) caused ectopic tail formation in the anterior blastema of body fragments, resulting in bipolar-tails regeneration. In contrast, RNAi of hedgehog (Djhh) and gli (Djgli) caused bipolar-heads regeneration. We show that Patched-mediated Hh signaling was crucial for posterior specification, which is established by regulating the transcription of Wnt genes via downstream Gli activity. Moreover, differentiated cells were responsible for the posterior specification of undifferentiated stem cells through Wnt/beta-catenin signaling. Surprisingly, Djhh was expressed in neural cells all along the ventral nerve cords (along the AP axis), but not in the posterior blastema of body fragments, where the expression of Wnt genes was induced for posteriorization. We therefore propose that Hh signals direct head or tail regeneration according to the AP polarity, which is established by Hh signaling activity along the body's preexisting nervous system.
Collapse
|
31
|
Tokhunts R, Singh S, Chu T, D'Angelo G, Baubet V, Goetz JA, Huang Z, Yuan Z, Ascano M, Zavros Y, Thérond PP, Kunes S, Dahmane N, Robbins DJ. The full-length unprocessed hedgehog protein is an active signaling molecule. J Biol Chem 2009; 285:2562-8. [PMID: 19920144 DOI: 10.1074/jbc.m109.078626] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The hedgehog (HH) family of ligands plays an important instructional role in metazoan development. HH proteins are initially produced as approximately 45-kDa full-length proteins, which undergo an intramolecular cleavage to generate an amino-terminal product that subsequently becomes cholesterol-modified (HH-Np). It is well accepted that this cholesterol-modified amino-terminal cleavage product is responsible for all HH-dependent signaling events. Contrary to this model we show here that full-length forms of HH proteins are able to traffic to the plasma membrane and participate directly in cell-cell signaling, both in vitro and in vivo. We were also able to rescue a Drosophila eye-specific hh loss of function phenotype by expressing a full-length form of hh that cannot be processed into HH-Np. These results suggest that in some physiological contexts full-length HH proteins may participate directly in HH signaling and that this novel activity of full-length HH may be evolutionarily conserved.
Collapse
Affiliation(s)
- Robert Tokhunts
- Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
32
|
Zhang Y, Chen D, Wang Z. Analyses of mental dysfunction-related ACSl4 in Drosophila reveal its requirement for Dpp/BMP production and visual wiring in the brain. Hum Mol Genet 2009; 18:3894-905. [PMID: 19617635 DOI: 10.1093/hmg/ddp332] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Long-chain acyl-CoA synthetases (ACSLs) convert long-chain fatty acids to acyl-CoAs, the activated substrates essential in various metabolic and signaling pathways. Mutations in ACSL4 are associated with non-syndromic X-linked mental retardation (MRX). However, the developmental functions of ACSL4 and how it is involved in the pathogenesis of MRX remain largely unknown. The Drosophila ACSL-like protein is highly homologous to human ACSL3 and ACSL4, and we designate it as dAcsl. In this study, we demonstrate that dAcsl and ACSL4 are highly conserved in terms of ACSL4's ability to substitute the functions of dAcsl in organismal viability, lipid storage and the neural wiring in visual center. In neurodevelopment, decapentaplegic (Dpp, a BMP-like molecule) production diminished specifically in the larval brain of dAcsl mutants. Consistent with the Dpp reduction, the number of glial cells and neurons dramatically decreased and the retinal axons mis-targeted in the visual cortex. All these defects in Drosophila brain were rescued by the wild-type ACSL4 but not by the mutant products found in MRX patients. Interestingly, expression of an MRX-associated ACSL4 mutant form in a wild-type background led to the lesions in visual center, suggesting a dominant negative effect. These findings validate Drosophila as a model system to reveal the connection between ACSL4 and BMP pathway in neurodevelopment, and to infer the pathogenesis of ACSL4-related MRX.
Collapse
Affiliation(s)
- Yi Zhang
- Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, People's Republic of China
| | | | | |
Collapse
|
33
|
Abstract
The optic lobes comprise approximately half of the fly's brain. In four major synaptic ganglia, or neuropils, the visual input from the compound eyes is received and processed for higher order visual functions like motion detection and color vision. A common characteristic of vertebrate and invertebrate visual systems is the point-to-point mapping of the visual world to synaptic layers in the brain, referred to as visuotopy. Vision requires the parallel extraction of numerous parameters in a visuotopic manner. Consequently, the optic neuropils are arranged in columns and perpendicularly oriented synaptic layers that allow for the selective establishment of synapses between columnar neurons. How this exquisite synaptic specificity is established during approximately 100 hours of brain development is still poorly understood. However, the optic lobe contains one of the best characterized brain structures in any organism-both anatomically and developmentally. Moreover, numerous molecules and their function illuminate some of the basic mechanisms involved in brain wiring. The emerging picture is that the development of the visual system of Drosophila is (epi-)genetically hard-wired; it supplies the emerging fly with vision without requiring neuronal activity for fine tuning of neuronal connectivity. Elucidating the genetic and cellular principles by which gene activity directs the assembly of the optic lobe is therefore a fascinating task and the focus of this chapter.
Collapse
|
34
|
Roignant JY, Treisman JE. Pattern formation in the Drosophila eye disc. THE INTERNATIONAL JOURNAL OF DEVELOPMENTAL BIOLOGY 2009; 53:795-804. [PMID: 19557685 PMCID: PMC2713679 DOI: 10.1387/ijdb.072483jr] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Differentiation of the Drosophila compound eye from the eye imaginal disc is a progressive process: columns of cells successively differentiate in a posterior to anterior sequence, clusters of cells form at regularly spaced intervals within each column, and individual photoreceptors differentiate in a defined order within each cluster. The progression of differentiation across the eye disc is driven by a positive autoregulatory loop of expression of the secreted molecule Hedgehog, which is temporally delayed by the intercalation of a second signal, Spitz. Hedgehog refines the spatial position at which each column initiates its differentiation by inducing secondary signals that act over different ranges to control the expression of positive and negative regulators. The position of clusters within each column is controlled by secreted inhibitory signals from clusters in the preceding column, and a single founder neuron, R8, is singled out within each cluster by Notch-mediated lateral inhibition. R8 then sequentially recruits surrounding cells to differentiate by producing a short-range signal, Spitz, which induces a secondary short-range signal, Delta. Intrinsic transcription factors act in combination with these two signals to produce cell-type diversity within the ommatidium. The Hedgehog and Spitz signals are transported along the photoreceptor axons and reused within the brain as long-range and local cues to trigger the differentiation and assembly of target neurons.
Collapse
Affiliation(s)
- Jean-Yves Roignant
- Kimmel Center for Biology and Medicine of the Skirball Institute, New York University School of Medicine, Department of Cell Biology, 540 First Avenue, New York, NY 10016
| | - Jessica E. Treisman
- Kimmel Center for Biology and Medicine of the Skirball Institute, New York University School of Medicine, Department of Cell Biology, 540 First Avenue, New York, NY 10016
| |
Collapse
|
35
|
Baker NE. Patterning signals and proliferation in Drosophila imaginal discs. Curr Opin Genet Dev 2007; 17:287-93. [PMID: 17624759 DOI: 10.1016/j.gde.2007.05.005] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Revised: 05/15/2007] [Accepted: 05/15/2007] [Indexed: 01/12/2023]
Abstract
Recent studies indicate that signaling pathways with well-known roles in patterning also directly regulate cell proliferation. During the differentiation of the retina, Hedgehog, Decapentaplegic, Notch and the EGF receptor regulate proliferation spatially through transcriptional regulation of string, dacapo, and as yet unidentified regulators of Retinoblastoma and Cyclin E/Cdk2 activities. In the developing wing, a novel response to discontinuities in Decapentaplegic signaling combines with concentration-dependent effects to achieve a uniform proliferation pattern in response to a Decapentaplegic gradient. Damage to growing tissues is repaired by transient Decapentaplegic and Wingless secretion from dying cells to induce compensatory proliferation. Diverse spatial patterns of fate specification and of proliferation can arise through distinct combinations of signaling pathways. Reminiscent of pattern formation, cell cycle effects of each signaling pathway differ in distinct developmental fields, making use of a variety of target genes.
Collapse
Affiliation(s)
- Nicholas E Baker
- Department of Molecular Genetics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
| |
Collapse
|
36
|
Wang Y, McMahon AP, Allen BL. Shifting paradigms in Hedgehog signaling. Curr Opin Cell Biol 2007; 19:159-65. [PMID: 17303409 DOI: 10.1016/j.ceb.2007.02.005] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2006] [Accepted: 02/06/2007] [Indexed: 11/30/2022]
Abstract
Hedgehog (Hh) signaling proteins regulate multiple developmental and adult homeostatic processes. A defining feature of Hh signaling is that relatively small changes in the concentration of Hh ligand elicit dramatically different cellular responses. As a result, the processing, release and trafficking of Hh ligands must be tightly regulated to ensure proper signaling. In addition, sensitive and specific intracellular signaling cascades are needed to interpret subtle differences in the level of Hh signal to execute an appropriate response. A detailed understanding of the mechanisms that regulate these responses is critical to shaping our view of this key regulatory system.
Collapse
Affiliation(s)
- Yu Wang
- Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA
| | | | | |
Collapse
|