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Abstract
Neuronal polarity sets the foundation for information processing and signal transmission within neural networks. However, fundamental question of how a neuron develops and maintains structurally and functionally distinct processes, axons and dendrites, is still an unclear. The simplicity and availability of practical genetic tools makes C. elegans as an ideal model to study neuronal polarity in vivo. In recent years, new studies have identified critical polarity molecules that function at different stages of neuronal polarization in C. elegans. This review focuses on how neurons guided by extrinsic cues, break symmetry, and subsequently recruit intracellular molecules to establish and maintain axon-dendrite polarity in vivo.
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Affiliation(s)
- Chan-Yen Ou
- Department of Biology, Howard Hughes Medical Institute, Stanford University, 385 Serra Mall, CA 94305, USA
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52
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Harterink M, Kim DH, Middelkoop TC, Doan TD, van Oudenaarden A, Korswagen HC. Neuroblast migration along the anteroposterior axis of C. elegans is controlled by opposing gradients of Wnts and a secreted Frizzled-related protein. Development 2011; 138:2915-24. [PMID: 21653614 PMCID: PMC3119304 DOI: 10.1242/dev.064733] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/27/2011] [Indexed: 12/24/2022]
Abstract
The migration of neuroblasts along the anteroposterior body axis of C. elegans is controlled by multiple Wnts that act partially redundantly to guide cells to their precisely defined final destinations. How positional information is specified by this system is, however, still largely unknown. Here, we used a novel fluorescent in situ hybridization methods to generate a quantitative spatiotemporal expression map of the C. elegans Wnt genes. We found that the five Wnt genes are expressed in a series of partially overlapping domains along the anteroposterior axis, with a predominant expression in the posterior half of the body. Furthermore, we show that a secreted Frizzled-related protein is expressed at the anterior end of the body axis, where it inhibits Wnt signaling to control neuroblast migration. Our findings reveal that a system of regionalized Wnt gene expression and anterior Wnt inhibition guides the highly stereotypic migration of neuroblasts in C. elegans. Opposing expression of Wnts and Wnt inhibitors has been observed in basal metazoans and in the vertebrate neurectoderm. Our results in C. elegans support the notion that a system of posterior Wnt signaling and anterior Wnt inhibition is an evolutionarily conserved principle of primary body axis specification.
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Affiliation(s)
- Martin Harterink
- Hubrecht Institute, Royal Academy of Arts and Sciences and University Medical Center Utrecht, Uppsalalaan 8, 3584 CT, Utrecht, The Netherlands
| | - Dong hyun Kim
- Department of Physics and department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
| | - Teije C. Middelkoop
- Hubrecht Institute, Royal Academy of Arts and Sciences and University Medical Center Utrecht, Uppsalalaan 8, 3584 CT, Utrecht, The Netherlands
| | - Thang Dinh Doan
- Hubrecht Institute, Royal Academy of Arts and Sciences and University Medical Center Utrecht, Uppsalalaan 8, 3584 CT, Utrecht, The Netherlands
| | - Alexander van Oudenaarden
- Hubrecht Institute, Royal Academy of Arts and Sciences and University Medical Center Utrecht, Uppsalalaan 8, 3584 CT, Utrecht, The Netherlands
- Department of Physics and department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
| | - Hendrik C. Korswagen
- Hubrecht Institute, Royal Academy of Arts and Sciences and University Medical Center Utrecht, Uppsalalaan 8, 3584 CT, Utrecht, The Netherlands
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53
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Olsson-Carter K, Slack FJ. The POU transcription factor UNC-86 controls the timing and ventral guidance of Caenorhabditis elegans axon growth. Dev Dyn 2011; 240:1815-25. [PMID: 21656875 DOI: 10.1002/dvdy.22667] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/24/2011] [Indexed: 01/24/2023] Open
Abstract
The in vivo mechanisms that coordinate the timing of axon growth and guidance are not well understood. In the Caenorhabditis elegans hermaphrodite specific neurons (HSNs), the lin-4 microRNA controls the stage of axon initiation independent of the UNC-40 and SAX-3 ventral guidance receptors. lin-4 loss-of-function mutants exhibit marked delays in axon outgrowth, while lin-4 overexpression leads to precocious growth in the L3 larval stage. Here, we show that loss of the POU transcription factor UNC-86 not only results in penetrant ventral axon growth defects in in the HSNs, but also causes processes to extend in the L1, three stages earlier than wild-type. This temporal shift is not dependent on UNC-40 or SAX-3, and does not require the presence of lin-4. We propose that unc-86(lf) HSN axons are misguided due to the temporal decoupling of axon initiation and ventral guidance responses.
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Affiliation(s)
- Katherine Olsson-Carter
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut, USA
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54
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Janssen R, Le Gouar M, Pechmann M, Poulin F, Bolognesi R, Schwager EE, Hopfen C, Colbourne JK, Budd GE, Brown SJ, Prpic NM, Kosiol C, Vervoort M, Damen WGM, Balavoine G, McGregor AP. Conservation, loss, and redeployment of Wnt ligands in protostomes: implications for understanding the evolution of segment formation. BMC Evol Biol 2010; 10:374. [PMID: 21122121 PMCID: PMC3003278 DOI: 10.1186/1471-2148-10-374] [Citation(s) in RCA: 122] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2010] [Accepted: 12/01/2010] [Indexed: 12/13/2022] Open
Abstract
Background The Wnt genes encode secreted glycoprotein ligands that regulate a wide range of developmental processes, including axis elongation and segmentation. There are thirteen subfamilies of Wnt genes in metazoans and this gene diversity appeared early in animal evolution. The loss of Wnt subfamilies appears to be common in insects, but little is known about the Wnt repertoire in other arthropods, and moreover the expression and function of these genes have only been investigated in a few protostomes outside the relatively Wnt-poor model species Drosophila melanogaster and Caenorhabditis elegans. To investigate the evolution of this important gene family more broadly in protostomes, we surveyed the Wnt gene diversity in the crustacean Daphnia pulex, the chelicerates Ixodes scapularis and Achaearanea tepidariorum, the myriapod Glomeris marginata and the annelid Platynereis dumerilii. We also characterised Wnt gene expression in the latter three species, and further investigated expression of these genes in the beetle Tribolium castaneum. Results We found that Daphnia and Platynereis both contain twelve Wnt subfamilies demonstrating that the common ancestors of arthropods, ecdysozoans and protostomes possessed all members of all Wnt subfamilies except Wnt3. Furthermore, although there is striking loss of Wnt genes in insects, other arthropods have maintained greater Wnt gene diversity. The expression of many Wnt genes overlap in segmentally reiterated patterns and in the segment addition zone, and while these patterns can be relatively conserved among arthropods and the annelid, there have also been changes in the expression of some Wnt genes in the course of protostome evolution. Nevertheless, our results strongly support the parasegment as the primary segmental unit in arthropods, and suggest further similarities between segmental and parasegmental regulation by Wnt genes in annelids and arthropods respectively. Conclusions Despite frequent losses of Wnt gene subfamilies in lineages such as insects, nematodes and leeches, most protostomes have probably maintained much of their ancestral repertoire of twelve Wnt genes. The maintenance of a large set of these ligands could be in part due to their combinatorial activity in various tissues rather than functional redundancy. The activity of such Wnt 'landscapes' as opposed to the function of individual ligands could explain the patterns of conservation and redeployment of these genes in important developmental processes across metazoans. This requires further analysis of the expression and function of these genes in a wider range of taxa.
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Affiliation(s)
- Ralf Janssen
- Department of Earth Sciences, Palaeobiology, Villavägen 16, SE-75236 Uppsala, Sweden
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55
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Banerjee D, Chen X, Lin SY, Slack FJ. kin-19/casein kinase Iα has dual functions in regulating asymmetric division and terminal differentiation in C. elegans epidermal stem cells. Cell Cycle 2010; 9:4748-65. [PMID: 21127398 DOI: 10.4161/cc.9.23.14092] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Casein Kinase I (CKI) is a conserved component of the Wnt signaling pathway, which regulates cell fate determination in metazoans. We show that post-embryonic asymmetric division and fate specification of C. elegans epidermal stem cells are controlled by a non-canonical Wnt/β-catenin signaling pathway, involving the β-catenins WRM-1 and SYS-1, and that C. elegans kin-19/CKIα functions in this pathway. Furthermore, we find that kin-19 is the only member of the Wnt asymmetry pathway that functions with, or in parallel to, the heterochronic temporal patterning pathway to control withdrawal from self-renewal and subsequent terminal differentiation of epidermal stem cells. We show that, except in the case of kin-19, the Wnt asymmetry pathway and the heterochronic pathway function separately and in parallel to control different aspects of epidermal stem cell fate specification. However, given the function of kin-19/CKIα in both pathways, and that CKI, Wnt signaling pathway and heterochronic pathway genes are widely conserved in animals, our findings suggest that CKIα may function as a regulatory hub through which asymmetric division and terminal differentiation are coordinated in adult stem cells of vertebrates.
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Affiliation(s)
- Diya Banerjee
- Department of Biological Sciences, Virginia Tech University, Blacksburg, VA, USA.
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56
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Gleason JE, Eisenmann DM. Wnt signaling controls the stem cell-like asymmetric division of the epithelial seam cells during C. elegans larval development. Dev Biol 2010; 348:58-66. [PMID: 20849842 PMCID: PMC2976807 DOI: 10.1016/j.ydbio.2010.09.005] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2009] [Revised: 08/06/2010] [Accepted: 09/06/2010] [Indexed: 10/19/2022]
Abstract
Metazoan stem cells repopulate tissues during adult life by dividing asymmetrically to generate another stem cell and a cell that terminally differentiates. Wnt signaling regulates the division pattern of stem cells in flies and vertebrates. While the short-lived nematode C. elegans has no adult somatic stem cells, the lateral epithelial seam cells divide in a stem cell-like manner in each larval stage, usually generating a posterior daughter that retains the seam cell fate and an anterior daughter that terminally differentiates. We show that while wild-type adult animals have 16 seam cells per side, animals with reduced function of the TCF homolog POP-1 have as many as 67 seam cells, and animals with reduced function of the β-catenins SYS-1 and WRM-1 have as few as three. Analysis of seam cell division patterns showed alterations in their stem cell-like divisions in the L2-L4 stages: reduced Wnt signaling caused both daughters to adopt non-seam fates, while activated Wnt signaling caused both daughters to adopt the seam fate. Therefore, our results indicate that Wnt signaling globally regulates the asymmetric, stem cell-like division of most or all somatic seam cells during C. elegans larval development, and that Wnt pathway regulation of stem cell-like behavior is conserved in nematodes.
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57
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Song S, Zhang B, Sun H, Li X, Xiang Y, Liu Z, Huang X, Ding M. A Wnt-Frz/Ror-Dsh pathway regulates neurite outgrowth in Caenorhabditis elegans. PLoS Genet 2010; 6:e1001056. [PMID: 20711352 PMCID: PMC2920835 DOI: 10.1371/journal.pgen.1001056] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2010] [Accepted: 07/08/2010] [Indexed: 11/18/2022] Open
Abstract
One of the challenges to understand the organization of the nervous system has been to determine how axon guidance molecules govern axon outgrowth. Through an unbiased genetic screen, we identified a conserved Wnt pathway which is crucial for anterior-posterior (A/P) outgrowth of neurites from RME head motor neurons in Caenorhabditis elegans. The pathway is composed of the Wnt ligand CWN-2, the Frizzled receptors CFZ-2 and MIG-1, the co-receptor CAM-1/Ror, and the downstream component Dishevelled/DSH-1. Among these, CWN-2 acts as a local attractive cue for neurite outgrowth, and its activity can be partially substituted with other Wnts, suggesting that spatial distribution plays a role in the functional specificity of Wnts. As a co-receptor, CAM-1 functions cell-autonomously in neurons and, together with CFZ-2 and MIG-1, transmits the Wnt signal to downstream effectors. Yeast two-hybrid screening identified DSH-1 as a binding partner for CAM-1, indicating that CAM-1 could facilitate CWN-2/Wnt signaling by its physical association with DSH-1. Our study reveals an important role of a Wnt-Frz/Ror-Dsh pathway in regulating neurite A/P outgrowth.
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Affiliation(s)
- Song Song
- Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China
- Graduate School, Chinese Academy of Sciences, Beijing, China
| | - Bo Zhang
- Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China
- Graduate School, Chinese Academy of Sciences, Beijing, China
| | - Hui Sun
- Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China
| | - Xia Li
- Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China
| | - Yanhui Xiang
- Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China
- Graduate School, Chinese Academy of Sciences, Beijing, China
| | - Zhonghua Liu
- Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China
| | - Xun Huang
- Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China
| | - Mei Ding
- Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China
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58
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Fleming T, Chien SC, Vanderzalm PJ, Dell M, Gavin MK, Forrester WC, Garriga G. The role of C. elegans Ena/VASP homolog UNC-34 in neuronal polarity and motility. Dev Biol 2010; 344:94-106. [PMID: 20452341 DOI: 10.1016/j.ydbio.2010.04.025] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2010] [Revised: 04/13/2010] [Accepted: 04/22/2010] [Indexed: 12/30/2022]
Abstract
Ena/VASP proteins mediate the effects of guidance cues on the actin cytoskeleton. The single C. elegans homolog of the Ena/VASP family of proteins, UNC-34, is required for the migrations of cells and growth cones. Here we show that unc-34 mutant alleles also interact genetically with Wnt mutants to reveal a role for unc-34 in the establishment of neuronal polarity along the C. elegans anterior-posterior axis. Our mutant analysis shows that eliminating UNC-34 function results in neuronal migration and polarity phenotypes that are enhanced at higher temperatures, revealing a heat-sensitive process that is normally masked by the presence of UNC-34. Finally, we show that the UNC-34 protein is expressed broadly and accumulates in axons and at the apical junctions of epithelial cells. While most mutants lacked detectable UNC-34, three unc-34 mutants that contained missense mutations in the EVH1 domain produced full-length UNC-34 that failed to localize to apical junctions and axons, supporting the role for the EVH1 domain in localizing Ena/VASP family members.
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Affiliation(s)
- Tinya Fleming
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA
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59
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Pasco MY, Catoire H, Parker JA, Brais B, Rouleau GA, Néri C. Cross-talk between canonical Wnt signaling and the sirtuin-FoxO longevity pathway to protect against muscular pathology induced by mutant PABPN1 expression in C. elegans. Neurobiol Dis 2010; 38:425-33. [PMID: 20227501 DOI: 10.1016/j.nbd.2010.03.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2009] [Revised: 02/24/2010] [Accepted: 03/04/2010] [Indexed: 10/19/2022] Open
Abstract
Developmental pathways may be play a role in adult cell survival. However, whether they interact with longevity/cell survival pathways to confer protection against disease-associated proteotoxicity remains largely unknown. We previously reported that the inhibition of key longevity modulators such as the deacetylase sir-2.1/SIRT1 (Sir2) and its target daf-16/FoxO protects transgenics nematodes from muscle cell decline and abnormal motility produced by the expression of mutant (polyalanine-expanded) PABPN1, the oculopharyngeal muscular dystrophy (OPMD) protein. Here, we report that canonical Wnt signaling (i) modulates muscular pathology in mutant PABPN1 nematodes, and (ii) cooperates with the Sir2-FoxO longevity pathway to confer protection against mutant PABPN1 toxicity at the cellular and behavioral levels. Mutant PABPN1 toxicity was modified by genes along the canonical Wnt pathway, several of which depend on daf-16 for activity. ss-catenin and pop-1/TCF RNAi suppressed the protection from mutant PABPN1 confered by loss-of-function mutations in sir-2.1 and daf-16. Moreover, the aggravation of muscle cell pathology by increased sir-2.1 dosage was reversed by ss-catenin and pop-1 RNAi. The chemical inhibition of GSK-3ss, a repressor of ss-catenin activity, protected against mutant PABPN1 toxicity in a daf-16-dependent manner, which is consistent with a cross-talk between ss-catenin signaling and Sir2-FoxO signaling in protecting from mutant PABPN1 toxicity. Our data reveal that canonical Wnt signaling and Sir2-FoxO signaling interact to modulate diseased muscle survival, and indicate that GSK-3ss inhibitors and sirtuin inhibitors both have therapeutic potential for muscle protection in OPMD.
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Affiliation(s)
- Matthieu Y Pasco
- Inserm, Unit 894, Laboratory of Neuronal Cell Biology and Pathology, 75014 Paris, France
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60
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Cabello J, Neukomm LJ, Günesdogan U, Burkart K, Charette SJ, Lochnit G, Hengartner MO, Schnabel R. The Wnt pathway controls cell death engulfment, spindle orientation, and migration through CED-10/Rac. PLoS Biol 2010; 8:e1000297. [PMID: 20126385 PMCID: PMC2814829 DOI: 10.1371/journal.pbio.1000297] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2009] [Accepted: 12/16/2009] [Indexed: 11/18/2022] Open
Abstract
Specificity in Wnt-mediated developmental processes, such as directional cell cleavage, migration, and engulfment of dead cells in C. elegans, arises from the use of distinct Wnt pathway signalling modules. Wnt signalling pathways have extremely diverse functions in animals, including induction of cell fates or tumours, guidance of cell movements during gastrulation, and the induction of cell polarity. Wnt can induce polar changes in cellular morphology by a remodelling of the cytoskeleton. However, how activation of the Frizzled receptor induces cytoskeleton rearrangement is not well understood. We show, by an in depth 4-D microscopy analysis, that the Caenorhabditis elegans Wnt pathway signals to CED-10/Rac via two separate branches to regulate modulation of the cytoskeleton in different cellular situations. Apoptotic cell clearance and migration of the distal tip cell require the MOM-5/Fz receptor, GSK-3 kinase, and APC/APR-1, which activate the CED-2/5/12 branch of the engulfment machinery. MOM-5 (Frizzled) thus can function as an engulfment receptor in C. elegans. Our epistatic analyses also suggest that the two partially redundant signalling pathways defined earlier for engulfment may act in a single pathway in early embryos. By contrast, rearrangement of mitotic spindles requires the MOM-5/Fz receptor, GSK-3 kinase, and β-catenins, but not the downstream factors LIT-1/NLK or POP-1/Tcf. Taken together, our results indicate that in multiple developmental processes, CED-10/Rac can link polar signals mediated by the Wnt pathway to rearrangements of the cytoskeleton. During development, processes such as cell division, fate determination, migration, and removal of dead cells occur in a directional (i.e., polar) manner. For example, cell divisions in the early embryo often occur in a directional manner to maintain specific cell–cell interactions. Later, during organ formation, tissues may be shaped through polar cell migration. During apoptosis, a neighbouring cell engulfing a cell corpse utilizes polar positional information to deform its cytoskeleton and migrate around the corpse. Wnt pathway signalling is a common mechanism by which cells establish polarity during development, but how a single Wnt signal is translated into different outcomes in different cellular or developmental contexts is not clear. Our data on C. elegans suggest that during diverse directional events—cell engulfment, mitotic spindle movement, and cell migration—different Wnt ligands or a specific signal from a cell corpse signals to the Wnt receptor Frizzled (MOM-5 in C. elegans) and on to the downstream factors CED-10/Rac. But specificity of the Wnt signal is mediated by the use of distinct intermediate signal transduction pathways. Our discovery that this pathway is also used for engulfment of cell corpses led us to propose that the two parallel pathways, originally described for engulfment of corpses, are indeed parts of one pathway involving Wnt pathway components.
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Affiliation(s)
- Juan Cabello
- Technische Universität Carolo Wilhelmina Braunschweig, Institut für Genetik, Braunschweig, Germany
- Instituto de Biología Molecular y Celular del Cáncer, Centro de Investigación del Cáncer, Universidad de Salamanca-CSIC, Campus Universitario Miguel de Unamuno s/n, Salamanca, Spain
| | - Lukas J. Neukomm
- Institute of Molecular Biology, University of Zurich, Zurich, Switzerland
| | - Ufuk Günesdogan
- Technische Universität Carolo Wilhelmina Braunschweig, Institut für Genetik, Braunschweig, Germany
| | - Katharina Burkart
- Technische Universität Carolo Wilhelmina Braunschweig, Institut für Genetik, Braunschweig, Germany
| | - Steve J. Charette
- Institute of Molecular Biology, University of Zurich, Zurich, Switzerland
| | - Günter Lochnit
- Biochemisches Institut, Universität Gießen, Gießen, Germany
| | | | - Ralf Schnabel
- Technische Universität Carolo Wilhelmina Braunschweig, Institut für Genetik, Braunschweig, Germany
- * E-mail:
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61
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Kennerdell JR, Fetter RD, Bargmann CI. Wnt-Ror signaling to SIA and SIB neurons directs anterior axon guidance and nerve ring placement in C. elegans. Development 2009; 136:3801-10. [PMID: 19855022 DOI: 10.1242/dev.038109] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Wnt signaling through Frizzled proteins guides posterior cells and axons in C. elegans into different spatial domains. Here we demonstrate an essential role for Wnt signaling through Ror tyrosine kinase homologs in the most prominent anterior neuropil, the nerve ring. A genetic screen uncovered cwn-2, the C. elegans homolog of Wnt5, as a regulator of nerve ring placement. In cwn-2 mutants, all neuronal structures in and around the nerve ring are shifted to an abnormal anterior position. cwn-2 is required at the time of nerve ring formation; it is expressed by cells posterior of the nerve ring, but its precise site of expression is not critical for its function. In nerve ring development, cwn-2 acts primarily through the Wnt receptor CAM-1 (Ror), together with the Frizzled protein MIG-1, with parallel roles for the Frizzled protein CFZ-2. The identification of CAM-1 as a CWN-2 receptor contrasts with CAM-1 action as a non-receptor in other C. elegans Wnt pathways. Cell-specific rescue of cam-1 and cell ablation experiments reveal a crucial role for the SIA and SIB neurons in positioning the nerve ring, linking Wnt signaling to specific cells that organize the anterior nervous system.
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Affiliation(s)
- Jason R Kennerdell
- Howard Hughes Medical Institute, Laboratory of Neural Circuits and Behavior, The Rockefeller University, New York, NY 10065, USA
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62
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Sánchez-Camacho C, Bovolenta P. Emerging mechanisms in morphogen-mediated axon guidance. Bioessays 2009; 31:1013-25. [PMID: 19705365 DOI: 10.1002/bies.200900063] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Early in animal development, gradients of secreted morphogenic molecules, such as Sonic hedgehog (Shh), Wnt and TGFbeta/Bmp family members, regulate cell proliferation and determine the fate and phenotype of the target cells by activating well-characterized signalling pathways, which ultimately control gene transcription. Shh, Wnt and TGFbeta/Bmp signalling also play an important and evolutionary conserved role in neural circuit assembly. They regulate neuronal polarization, axon and dendrite development and synaptogenesis, processes that require rapid and local changes in cytoskeletal organization and plasma membrane components. A key question then is whether morphogen signalling at the growth cone uses similar mechanisms and intracellular pathway components to those described for morphogen-mediated cell specification. This review discusses recent advances towards the understanding of this problem, showing how Shh, Wnt and TGFbeta/Bmp have adapted their 'classical' signalling pathways or adopted alternative and novel molecular mechanisms to influence different aspects of neuronal circuit formation.
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Affiliation(s)
- Cristina Sánchez-Camacho
- Departamento de Neurobiología Molecular, Celular y del Desarrollo, Instituto Cajal, CSIC and CIBER de Enfermedades Raras (CIBERER), Madrid, Spain
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63
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van Amerongen R, Nusse R. Towards an integrated view of Wnt signaling in development. Development 2009; 136:3205-14. [PMID: 19736321 DOI: 10.1242/dev.033910] [Citation(s) in RCA: 890] [Impact Index Per Article: 59.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Wnt signaling is crucial for embryonic development in all animal species studied to date. The interaction between Wnt proteins and cell surface receptors can result in a variety of intracellular responses. A key remaining question is how these specific responses take shape in the context of a complex, multicellular organism. Recent studies suggest that we have to revise some of our most basic ideas about Wnt signal transduction. Rather than thinking about Wnt signaling in terms of distinct, linear, cellular signaling pathways, we propose a novel view that considers the integration of multiple, often simultaneous, inputs at the level of both Wnt-receptor binding and the downstream, intracellular response.
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Affiliation(s)
- Renée van Amerongen
- Department of Developmental Biology and Howard Hughes Medical Institute, Beckman Center, 279 Campus Drive, Stanford University, Stanford, CA 94305, USA
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64
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SDN-1/syndecan regulates growth factor signaling in distal tip cell migrations in C. elegans. Dev Biol 2009; 334:235-42. [DOI: 10.1016/j.ydbio.2009.07.020] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2009] [Revised: 06/11/2009] [Accepted: 07/16/2009] [Indexed: 12/18/2022]
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65
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Green JL, Kuntz SG, Sternberg PW. Ror receptor tyrosine kinases: orphans no more. Trends Cell Biol 2008; 18:536-44. [PMID: 18848778 PMCID: PMC4672995 DOI: 10.1016/j.tcb.2008.08.006] [Citation(s) in RCA: 182] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2008] [Revised: 08/28/2008] [Accepted: 08/28/2008] [Indexed: 12/13/2022]
Abstract
Receptor tyrosine kinase-like orphan receptor (Ror) proteins are a conserved family of tyrosine kinase receptors that function in developmental processes including skeletal and neuronal development, cell movement and cell polarity. Although Ror proteins were originally named because the associated ligand and signaling pathway were unknown, recent studies in multiple species have now established that Ror proteins are Wnt receptors. Depending on the cellular context, Ror proteins can either activate or repress transcription of Wnt target genes and can modulate Wnt signaling by sequestering Wnt ligands. New evidence implicates Ror proteins in planar cell polarity, an alternative Wnt pathway. Here, we review the progress made in understanding these mysterious proteins and, in particular, we focus on their function as Wnt receptors.
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Affiliation(s)
- Jennifer L Green
- Department of Developmental Biology, Stanford University School of Medicine, Beckman Center, B269, 279 Campus Drive, Stanford, CA 94305-5323, USA.
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66
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Chapman JO, Li H, Lundquist EA. The MIG-15 NIK kinase acts cell-autonomously in neuroblast polarization and migration in C. elegans. Dev Biol 2008; 324:245-57. [PMID: 18840424 DOI: 10.1016/j.ydbio.2008.09.014] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2008] [Revised: 08/11/2008] [Accepted: 09/12/2008] [Indexed: 11/25/2022]
Abstract
Cell migration is a fundamental process in animal development, including development of the nervous system. In C. elegans, the bilateral QR and QL neuroblasts undergo initial anterior and posterior polarizations and migrations before they divide to produce neurons. A subsequent Wnt signal from the posterior instructs QL descendants to continue their posterior migration. Nck-interacting kinases (NIK kinases) have been implicated in cell and nuclear migration as well as lamellipodia formation. Studies here show that the C. elegans MIG-15 NIK kinase controls multiple aspects of initial Q cell polarization, including the ability of the cells to polarize, to maintain polarity, and to migrate. These data suggest that MIG-15 acts independently of the Wnt signal that controls QL descendant posterior migration. Furthermore, MIG-15 affects the later migrations of neurons generated from Q cell division. Finally, a mosaic analysis indicates that MIG-15 acts cell-autonomously in Q descendant migration.
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Affiliation(s)
- Jamie O Chapman
- Department of Molecular Biosciences, University of Kansas, 1200 Sunnyside Avenue, Lawrence, KS 66045-7534, USA
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Killeen MT, Sybingco SS. Netrin, Slit and Wnt receptors allow axons to choose the axis of migration. Dev Biol 2008; 323:143-51. [PMID: 18801355 DOI: 10.1016/j.ydbio.2008.08.027] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2008] [Revised: 08/15/2008] [Accepted: 08/26/2008] [Indexed: 01/25/2023]
Abstract
One of the challenges to understanding nervous system development has been to establish how a fairly limited number of axon guidance cues can set up the patterning of very complex nervous systems. Studies on organisms with relatively simple nervous systems such as Drosophila melanogaster and C. elegans have provided many insights into axon guidance mechanisms. The axons of many neurons migrate along both the dorsal-ventral (DV) and the anterior-posterior (AP) axes at different phases of development, and in addition they may also cross the midline. Axon migration in the dorsal-ventral (DV) direction is mainly controlled by Netrins with their receptors; UNC-40/DCC and UNC-5, and the Slits with their receptors; Robo/SAX-3. Axon guidance in the anterior-posterior (AP) axis is mainly controlled by Wnts with their receptors; the Frizzleds/Fz. An individual axon may be subjected to opposing attractive and repulsive forces coming from opposite sides in the same axis but there may also be opposing cues in the other axis of migration. All the information from the cues has to be integrated within the growth cone at the leading edge of the migrating axon to elicit a response. Recent studies have provided insight into how this is achieved. Evidence suggests that the axis of axon migration is determined by the manner in which Netrin, Slit and Wnt receptors are polarized (localized) within the neuron prior to axon outgrowth. The same molecules are involved in both axon outgrowth and axon guidance, for at least some neurons in C. elegans, whether the cue is the attractive cue UNC-6/Netrin working though UNC-40/DCC or the repulsive cue SLT-1/Slit working though the receptor SAX-3/Robo (Adler et al., 2006, Chang et al., 2006, Quinn et al., 2006, 2008). The molecules involved in cell signaling in this case are polarized within the cell body of the neuron before process outgrowth and direct the axon outgrowth. Expression of the Netrin receptor UNC-40/DCC or the Slit receptor SAX-3/Robo in axons that normally migrate in the AP direction causes neuronal polarity reversal in a Netrin and Slit independent manner (Levy-Strumpf and Culotti 2007, Watari-Goshima et al., 2007). Localization of the receptors in this case is caused by the kinesin-related VAB-8L which appears to govern the site of axon outgrowth in these neurons by causing receptor localization. Therefore, asymmetric localization of axon guidance receptors is followed by axon outgrowth in vivo using the receptor's normal cue, either attractive, repulsive or unknown cues.
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Affiliation(s)
- Marie T Killeen
- Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, Ontario, Canada M5B 2K3.
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