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Karalis V, Wood D, Teaney NA, Sahin M. The role of TSC1 and TSC2 proteins in neuronal axons. Mol Psychiatry 2024; 29:1165-1178. [PMID: 38212374 DOI: 10.1038/s41380-023-02402-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2023] [Revised: 12/20/2023] [Accepted: 12/22/2023] [Indexed: 01/13/2024]
Abstract
Tuberous Sclerosis Complex 1 and 2 proteins, TSC1 and TSC2 respectively, participate in a multiprotein complex with a crucial role for the proper development and function of the nervous system. This complex primarily acts as an inhibitor of the mechanistic target of rapamycin (mTOR) kinase, and mutations in either TSC1 or TSC2 cause a neurodevelopmental disorder called Tuberous Sclerosis Complex (TSC). Neurological manifestations of TSC include brain lesions, epilepsy, autism, and intellectual disability. On the cellular level, the TSC/mTOR signaling axis regulates multiple anabolic and catabolic processes, but it is not clear how these processes contribute to specific neurologic phenotypes. Hence, several studies have aimed to elucidate the role of this signaling pathway in neurons. Of particular interest are axons, as axonal defects are associated with severe neurocognitive impairments. Here, we review findings regarding the role of the TSC1/2 protein complex in axons. Specifically, we will discuss how TSC1/2 canonical and non-canonical functions contribute to the formation and integrity of axonal structure and function.
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Affiliation(s)
- Vasiliki Karalis
- Rosamund Stone Zander Translational Neuroscience Center, Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA, 02115, USA
- FM Kirby Neurobiology Center, Boston Children's Hospital, Boston, MA, 02115, USA
| | - Delaney Wood
- FM Kirby Neurobiology Center, Boston Children's Hospital, Boston, MA, 02115, USA
- Human Neuron Core, Boston Children's Hospital, Boston, MA, 02115, USA
| | - Nicole A Teaney
- Rosamund Stone Zander Translational Neuroscience Center, Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA, 02115, USA
- FM Kirby Neurobiology Center, Boston Children's Hospital, Boston, MA, 02115, USA
| | - Mustafa Sahin
- Rosamund Stone Zander Translational Neuroscience Center, Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA, 02115, USA.
- FM Kirby Neurobiology Center, Boston Children's Hospital, Boston, MA, 02115, USA.
- Human Neuron Core, Boston Children's Hospital, Boston, MA, 02115, USA.
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2
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Zheng R, Xie M, Keyhani NO, Xia Y. An insect chemosensory protein facilitates locust avoidance to fungal pathogens via recognition of fungal volatiles. Int J Biol Macromol 2023; 253:127389. [PMID: 37827395 DOI: 10.1016/j.ijbiomac.2023.127389] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2023] [Revised: 09/16/2023] [Accepted: 10/09/2023] [Indexed: 10/14/2023]
Abstract
Locusts (Locusta migratoria) are one of the most destructive insect pests worldwide. Entomopathogenic fungi can infect and kill locusts, with Metarhizium acridum having evolved as a specialized acridid pathogen. However, locusts have evolved countermeasures to limit or avoid microbial pathogens, although the underlying molecular mechanisms behind these defenses remain obscure. Here, we demonstrate that L. migratoria exhibit avoidance behaviors towards M. acridum contaminated food via recognition of fungal volatiles, with locust perception of the volatile mediated by the LmigCSP60 chemosensory protein. RNAi-knockdown of LmigCSP60 lowered locust M. acridum avoidance behavior and increased infection and mortality. The fungal volatile, 2-phenylethanol (PEA), was identified to participate in locust behavioral avoidance. RNAi-knockdown of LmigCSP60 reduced antennal electrophysiological responses to PEA and impaired locust avoidance to the compound. Purified LmigCSP60 was able to bind a set of fungal volatiles including PEA. Furthermore, reduction of PEA emission by M. acridum via construction of a targeted gene knockout mutant of the alcohol dehydrogenase gene (ΔMaAdh strain) that contributes to PEA production reduced locust avoidance behavior towards the pathogen. These findings identify an olfactory circuit used by locusts to detect and avoid potential microbial pathogens before they are capable of initiating infection and highlight behavioral and olfactory adaptations affecting the co-evolution of host-pathogen interactions.
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Affiliation(s)
- Renwen Zheng
- School of Life Sciences, Chongqing University, Chongqing 401331, China; Chongqing Engineering Research Center for Fungal Insecticides, Chongqing 401331, China; Key Laboratory of Gene Function and Regulation Technologies under Chongqing Municipal Education Commission, Chongqing, China; School of Plant Protection, Anhui Agricultural University, Hefei 230036, China; Key Laboratory of Biology and Sustainable Management of Plant Diseases and Pests of Anhui Higher Education Institutes, Anhui Agricultural University, Hefei 230036, China.
| | - Mushan Xie
- School of Life Sciences, Chongqing University, Chongqing 401331, China; Chongqing Engineering Research Center for Fungal Insecticides, Chongqing 401331, China; Key Laboratory of Gene Function and Regulation Technologies under Chongqing Municipal Education Commission, Chongqing, China
| | - Nemat O Keyhani
- School of Life Sciences, Chongqing University, Chongqing 401331, China; Department of Biological Sciences, University of Illinois, Chicago, IL 60607, USA.
| | - Yuxian Xia
- School of Life Sciences, Chongqing University, Chongqing 401331, China; Chongqing Engineering Research Center for Fungal Insecticides, Chongqing 401331, China; Key Laboratory of Gene Function and Regulation Technologies under Chongqing Municipal Education Commission, Chongqing, China.
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3
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Salim S, Banu A, Alwa A, Gowda SBM, Mohammad F. The gut-microbiota-brain axis in autism: what Drosophila models can offer? J Neurodev Disord 2021; 13:37. [PMID: 34525941 PMCID: PMC8442445 DOI: 10.1186/s11689-021-09378-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Accepted: 08/06/2021] [Indexed: 12/28/2022] Open
Abstract
The idea that alterations in gut-microbiome-brain axis (GUMBA)-mediated communication play a crucial role in human brain disorders like autism remains a topic of intensive research in various labs. Gastrointestinal issues are a common comorbidity in patients with autism spectrum disorder (ASD). Although gut microbiome and microbial metabolites have been implicated in the etiology of ASD, the underlying molecular mechanism remains largely unknown. In this review, we have summarized recent findings in human and animal models highlighting the role of the gut-brain axis in ASD. We have discussed genetic and neurobehavioral characteristics of Drosophila as an animal model to study the role of GUMBA in ASD. The utility of Drosophila fruit flies as an amenable genetic tool, combined with axenic and gnotobiotic approaches, and availability of transgenic flies may reveal mechanistic insight into gut-microbiota-brain interactions and the impact of its alteration on behaviors relevant to neurological disorders like ASD.
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Affiliation(s)
- Safa Salim
- Division of Biological and Biomedical Sciences (BBS), College of Health & Life Sciences (CHLS), Hamad Bin Khalifa University (HBKU), Doha, 34110, Qatar
| | - Ayesha Banu
- Division of Biological and Biomedical Sciences (BBS), College of Health & Life Sciences (CHLS), Hamad Bin Khalifa University (HBKU), Doha, 34110, Qatar
| | - Amira Alwa
- Division of Biological and Biomedical Sciences (BBS), College of Health & Life Sciences (CHLS), Hamad Bin Khalifa University (HBKU), Doha, 34110, Qatar
| | - Swetha B M Gowda
- Division of Biological and Biomedical Sciences (BBS), College of Health & Life Sciences (CHLS), Hamad Bin Khalifa University (HBKU), Doha, 34110, Qatar
| | - Farhan Mohammad
- Division of Biological and Biomedical Sciences (BBS), College of Health & Life Sciences (CHLS), Hamad Bin Khalifa University (HBKU), Doha, 34110, Qatar.
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Zheng R, Xia Y, Keyhani NO. Differential responses of the antennal proteome of male and female migratory locusts to infection by a fungal pathogen. J Proteomics 2020; 232:104050. [PMID: 33217581 DOI: 10.1016/j.jprot.2020.104050] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Revised: 11/04/2020] [Accepted: 11/15/2020] [Indexed: 11/24/2022]
Abstract
The narrow host range entomopathogenic fungus, Metarhizium acridum, is an environmentally friendly acridid specific pathogen used for locust control. The locust is capable of responding within hours of infection, however, little is known concerning how the locust detects the pathogen. Here, we have identified 3213 proteins in the infected antennal proteome of the migratory locust, Locusta migratoria. iTRAQ comparative analyses of antennal proteomes identified 194 differentially abundant proteins (DAPs) between uninfected and infected males, 218 DAPs between uninfected and infected females, and 240 DAPs between infected males and infected females. In relation to olfaction, a total of 29 chemosensory proteins (CSPs), 9 odorant binding proteins (OBPs), 31 odorant receptors (ORs), and 8 ionotropic receptors (IRs) were differentially abundant after M. acridum infection, with a subset of 12 proteins found in both infected male and female antennae not present in uninfected individuals. The time course of the gene expression profiles of olfaction related DAPs were investigated by quantitative real-time PCR (qRT-PCR). Our data indicate significant changes in the antennal proteomes of male and female locusts in response to a microbial pathogen, highlighting the potential participation of olfactory processes in pathogen detection and response. BIOLOGICAL SIGNIFICANCE: The ability of an organism to detect microbial pathogens is essential for mounting a response to mitigate the spread of the infection. Using iTRAQ-based proteomic analyses changes in the protein repertoire of the antennae of male and female locusts in response to infection by a host-specific pathogen were determined. These data show proteomic alterations that are also sex-specific, identifying members of olfactory pathways that are modified in response to infection. Our data identify antennal and related olfactory proteins that are candidates for mediating host detection of pathogens, and that may contribute to subsequent behavioral and/or immune responses of the host to the infection challenge.
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Affiliation(s)
- Renwen Zheng
- School of Life Sciences, Chongqing University, Chongqing Engineering Research Center for Fungal Insecticides, Chongqing 400030, China
| | - Yuxian Xia
- School of Life Sciences, Chongqing University, Chongqing Engineering Research Center for Fungal Insecticides, Chongqing 400030, China.
| | - Nemat O Keyhani
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Bldg. 981, Museum Rd., Gainesville FL32611, USA.
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5
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Yin J, Schaaf CP. Autism genetics - an overview. Prenat Diagn 2016; 37:14-30. [DOI: 10.1002/pd.4942] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2016] [Revised: 10/04/2016] [Accepted: 10/11/2016] [Indexed: 12/13/2022]
Affiliation(s)
- Jiani Yin
- Department of Molecular and Human Genetics; Baylor College of Medicine; Houston TX USA
- Jan and Dan Duncan Neurological Research Institute at Texas Children's Hospital; Houston TX USA
| | - Christian P. Schaaf
- Department of Molecular and Human Genetics; Baylor College of Medicine; Houston TX USA
- Jan and Dan Duncan Neurological Research Institute at Texas Children's Hospital; Houston TX USA
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Kays I, Cvetkovska V, Chen BE. Structural and functional analysis of single neurons to correlate synaptic connectivity with grooming behavior. Nat Protoc 2013; 9:1-10. [PMID: 24309972 DOI: 10.1038/nprot.2013.157] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
We describe a protocol to image the complex axonal branching structure of identified mechanosensory neurons in Drosophila, combined with a behavioral assay to evaluate the functional output of the neuron. The stimulation of identified mechanosensory neurons in live animals produces a stereotyped grooming reflex. The mechanosensory axonal arbor within the CNS is subsequently labeled with a lipophilic fluorescent dye and imaged by fluorescence microscopy. The behavioral output can therefore be correlated to the axonal morphology of the stimulated neuron in the same animal. Combining this protocol with genetic analysis provides a powerful tool for identifying the roles of molecules involved in different aspects of hard-wired neural circuit formation underlying an innate behavior. From behavioral analysis to axonal imaging, the protocol takes 4 d.
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Affiliation(s)
- Ibrahim Kays
- 1] Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montréal, Québec, Canada. [2]
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Grooming Behavior as a Mechanism of Insect Disease Defense. INSECTS 2013; 4:609-30. [PMID: 26462526 PMCID: PMC4553506 DOI: 10.3390/insects4040609] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/26/2013] [Revised: 10/20/2013] [Accepted: 10/22/2013] [Indexed: 11/17/2022]
Abstract
Grooming is a well-recognized, multipurpose, behavior in arthropods and vertebrates. In this paper, we review the literature to highlight the physical function, neurophysiological mechanisms, and role that grooming plays in insect defense against pathogenic infection. The intricate relationships between the physical, neurological and immunological mechanisms of grooming are discussed to illustrate the importance of this behavior when examining the ecology of insect-pathogen interactions.
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8
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Cvetkovska V, Hibbert AD, Emran F, Chen BE. Overexpression of Down syndrome cell adhesion molecule impairs precise synaptic targeting. Nat Neurosci 2013; 16:677-82. [PMID: 23666178 PMCID: PMC3954815 DOI: 10.1038/nn.3396] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2012] [Accepted: 04/10/2013] [Indexed: 12/17/2022]
Abstract
Fragile X syndrome is caused by loss of Fragile X Mental Retardation Protein (FMRP), an RNA binding protein that suppresses protein translation. Here, we identified Down Syndrome Cell Adhesion Molecule (Dscam) RNA, a molecule involved in neural development and implicated in Down syndrome, bound to FMRP. Elevated Dscam protein levels in Drosophila FMRP null animals and in animals with three copies of the Dscam gene both produced specific and similar synaptic targeting errors in a hard-wired neural circuit which impaired the animal’s sensory perception. Reducing Dscam levels in FMRP null animals reduced synaptic targeting errors and rescued behavioral responses. Our results demonstrate that excess Dscam protein may be a common molecular mechanism underlying altered neural wiring in major causes of intellectual disability.
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Affiliation(s)
- Vedrana Cvetkovska
- Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montréal, Québec, Canada
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Neufeld SQ, Hibbert AD, Chen BE. Opposing roles of PlexinA and PlexinB in axonal branch and varicosity formation. Mol Brain 2011; 4:15. [PMID: 21489263 PMCID: PMC3094289 DOI: 10.1186/1756-6606-4-15] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2011] [Accepted: 04/13/2011] [Indexed: 01/01/2023] Open
Abstract
Establishing precise synaptic connectivity during development is crucial for neural circuit function. However, very few molecules have been identified that are involved in determining where and how many synapses form. The Plexin cell-surface molecules are a conserved family of axon guidance receptors that mediate axon fasciculation and repulsion during neural development, and later in development PlexinA receptors are involved in eliminating axonal branches and synapse numbers. Here we investigate the roles of PlexinA and PlexinB receptors in axonal branch and varicosity formation in Drosophila. We knocked down PlexinA or PlexinB expression using RNAi in identified mechanosensory neurons and analyzed axonal branching patterns and varicosity formations. Reducing PlexinA expression increased the axonal arbor complexity by increasing the number of branches and varicosities along the axon. In contrast, knocking down PlexinB expression decreased morphological complexity by decreasing the number of branches and the overall size of the axonal arbor, but did not reduce the number of varicosities. Our results demonstrate opposing roles for PlexinA and PlexinB in local wiring within a target region, where PlexinA functions to suppress excessive axonal branches and synapses and PlexinB facilitates axonal growth.
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Affiliation(s)
- Shay Q Neufeld
- Research Institute of the McGill University Health Centre, Centre for Research in Neuroscience, Montréal, Québec, Canada
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10
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de Luca A, Vassallo S, Benitez-Temino B, Menichetti G, Rossi F, Buffo A. Distinct modes of neuritic growth in purkinje neurons at different developmental stages: axonal morphogenesis and cellular regulatory mechanisms. PLoS One 2009; 4:e6848. [PMID: 19718257 PMCID: PMC2729392 DOI: 10.1371/journal.pone.0006848] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2009] [Accepted: 07/15/2009] [Indexed: 11/19/2022] Open
Abstract
Background During development, neurons modify their axon growth mode switching from an elongating phase, in which the main axon stem reaches the target territory through growth cone-driven extension, to an arborising phase, when the terminal arbour is formed to establish synaptic connections. To investigate the relative contribution of cell-autonomous factors and environmental signals in the control of these distinct axon growth patterns, we examined the neuritogenesis of Purkinje neurons in cerebellar cultures prepared at elongating (embryonic day 17) or arborising (postnatal day zero) stages of Purkinje axon maturation. Methodology/Principal Findings When placed in vitro, Purkinje cells of both ages undergo an initial phase of neurite elongation followed by the development of terminal ramifications. Nevertheless, elongation of the main axon stem prevails in embryonic Purkinje axons, and many of these neurons are totally unable to form terminal branches. On the contrary, all postnatal neurites switch to arbour growth within a few days in culture and spread extensive terminal trees. Regardless of their elongating or arborising pattern, defined growth features (e.g. growth rate and tree extension) of embryonic Purkinje axons remain distinct from those of postnatal neurites. Thus, Purkinje neurons of different ages are endowed with intrinsic stage-specific competence for neuritic growth. Such competence, however, can be modified by environmental cues. Indeed, while exposure to the postnatal environment stimulates the growth of embryonic axons without modifying their phenotype, contact-mediated signals derived from granule cells specifically induce arborising growth and modulate the dynamics of neuritic elongation. Conclusions/Significance Cultured Purkinje cells recapitulate an intrinsically coded neuritogenic program, involving initial navigation of the axon towards the target field and subsequent expansion of the terminal arborisation. The execution of this program is regulated by environmental signals that modify the growth competence of Purkinje cells, so to adapt their endogenous properties to the different phases of neuritic morphogenesis.
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Affiliation(s)
| | | | | | | | - Ferdinando Rossi
- Department of Neuroscience, University of Turin, Turin, Italy
- Neuroscience Institute of Turin (NIT), Turin, Italy
- Rita Levi-Montalcini Center for Brain Repair, National Institute of Neuroscience, Turin, Italy
| | - Annalisa Buffo
- Department of Neuroscience, University of Turin, Turin, Italy
- Neuroscience Institute of Turin (NIT), Turin, Italy
- * E-mail:
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Gomez-Diaz C, Alcorta E. Quantitative analysis of antennal mosaic generation in Drosophila melanogaster by the MARCM system. Genesis 2008; 46:283-8. [PMID: 18543310 DOI: 10.1002/dvg.20394] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Mosaics have been used in Drosophila to study development and to generate mutant structures when a mutant allele is homozygous lethal. New approaches of directed somatic recombination based on FRT/FLP methods, have increased mosaicism rates but likewise multiple clones in the same individual appeared more frequently. Production of single clones could be essential for developmental studies; however, for cell-autonomous gene function studies only the presence of homozygous cells for the target recessive allele is relevant. Herein, we report the number and extension of antennal mosaics generated by the MARCM system at different ages. This information is directed to obtain the appropriated mosaic type for the intended application. By applying heat shock at 10 different developmental stages from 0-12 h to 6-7 days after egg laying, more than 50% of mosaics were obtained from 5,028 adults. Single recombinant clones appeared mainly at early stages while massive recombinant areas were observed with late treatments.
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Disruption of Esrom and Ryk identifies the roof plate boundary as an intermediate target for commissure formation. Mol Cell Neurosci 2007; 37:271-83. [PMID: 18060805 DOI: 10.1016/j.mcn.2007.10.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2007] [Accepted: 10/10/2007] [Indexed: 01/14/2023] Open
Abstract
Growth cones are guided to their final destination by intermediate targets. Here, we identify intermediate targets and signaling components acting on zebrafish habenula commissural axons. Live imaging establishes that axons pause at the medial habenula before and after crossing the roof plate. esrom mutants axons fail to advance beyond the ipsilateral medial habenula. Tsc2 function is reduced in mutant axons, indicating cell autonomous defects in signaling. Consistent with signaling properties changing outside the roof plate, EphB is surface localized on axon segments within a zone demarcated by the medial habenula. wnt4a is expressed in the medial habenula and morpholino knockdown causes loss of the commissure. Electroporation of truncated Ryk causes axons to reenter the midline after reaching the contralateral habenula. These data identify Esrom as a mediator of growth cone navigation at an intermediate target and underscore the importance of midline boundaries as signaling centers for commissure formation.
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Abstract
Dendrites from the same neuron usually avoid contact with one another, a behavior known as self-avoidance. In this issue of Neuron and in the upcoming May 4, 2007 issue of Cell, a pair of studies by Soba et al. and Hughes et al. and a study by Matthews et al., respectively, identify products from the highly alternatively spliced Dscam gene as central to this behavior in Drosophila. Signaling induced by adhesion between identical isoforms triggers repulsion between sister dendrites.
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Affiliation(s)
- Thomas Kidd
- Biology Department/MS 314, University of Nevada, Reno, NV 89557, USA.
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Sánchez-Soriano N, Tear G, Whitington P, Prokop A. Drosophila as a genetic and cellular model for studies on axonal growth. Neural Dev 2007; 2:9. [PMID: 17475018 PMCID: PMC1876224 DOI: 10.1186/1749-8104-2-9] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2007] [Accepted: 05/02/2007] [Indexed: 11/10/2022] Open
Abstract
One of the most fascinating processes during nervous system development is the establishment of stereotypic neuronal networks. An essential step in this process is the outgrowth and precise navigation (pathfinding) of axons and dendrites towards their synaptic partner cells. This phenomenon was first described more than a century ago and, over the past decades, increasing insights have been gained into the cellular and molecular mechanisms regulating neuronal growth and navigation. Progress in this area has been greatly assisted by the use of simple and genetically tractable invertebrate model systems, such as the fruit fly Drosophila melanogaster. This review is dedicated to Drosophila as a genetic and cellular model to study axonal growth and demonstrates how it can and has been used for this research. We describe the various cellular systems of Drosophila used for such studies, insights into axonal growth cones and their cytoskeletal dynamics, and summarise identified molecular signalling pathways required for growth cone navigation, with particular focus on pathfinding decisions in the ventral nerve cord of Drosophila embryos. These Drosophila-specific aspects are viewed in the general context of our current knowledge about neuronal growth.
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Affiliation(s)
- Natalia Sánchez-Soriano
- The Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, The University of Manchester, Manchester, UK
| | - Guy Tear
- MRC Centre for Developmental Neurobiology, Guy's Campus, King's College, London, UK
| | - Paul Whitington
- Department of Anatomy and Cell Biology, University of Melbourne, Victoria, Australia
| | - Andreas Prokop
- The Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, The University of Manchester, Manchester, UK
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15
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Knox S, Ge H, Dimitroff BD, Ren Y, Howe KA, Arsham AM, Easterday MC, Neufeld TP, O'Connor MB, Selleck SB. Mechanisms of TSC-mediated control of synapse assembly and axon guidance. PLoS One 2007; 2:e375. [PMID: 17440611 PMCID: PMC1847706 DOI: 10.1371/journal.pone.0000375] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2006] [Accepted: 03/19/2007] [Indexed: 01/13/2023] Open
Abstract
Tuberous sclerosis complex is a dominant genetic disorder produced by mutations in either of two tumor suppressor genes, TSC1 and TSC2; it is characterized by hamartomatous tumors, and is associated with severe neurological and behavioral disturbances. Mutations in TSC1 or TSC2 deregulate a conserved growth control pathway that includes Ras homolog enriched in brain (Rheb) and Target of Rapamycin (TOR). To understand the function of this pathway in neural development, we have examined the contributions of multiple components of this pathway in both neuromuscular junction assembly and photoreceptor axon guidance in Drosophila. Expression of Rheb in the motoneuron, but not the muscle of the larval neuromuscular junction produced synaptic overgrowth and enhanced synaptic function, while reductions in Rheb function compromised synapse development. Synapse growth produced by Rheb is insensitive to rapamycin, an inhibitor of Tor complex 1, and requires wishful thinking, a bone morphogenetic protein receptor critical for functional synapse expansion. In the visual system, loss of Tsc1 in the developing retina disrupted axon guidance independently of cellular growth. Inhibiting Tor complex 1 with rapamycin or eliminating the Tor complex 1 effector, S6 kinase (S6k), did not rescue axon guidance abnormalities of Tsc1 mosaics, while reductions in Tor function suppressed those phenotypes. These findings show that Tsc-mediated control of axon guidance and synapse assembly occurs via growth-independent signaling mechanisms, and suggest that Tor complex 2, a regulator of actin organization, is critical in these aspects of neuronal development.
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Affiliation(s)
- Sarah Knox
- The Developmental Biology Center, Department of Pediatrics, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Hong Ge
- The Developmental Biology Center, Department of Pediatrics, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Brian D. Dimitroff
- The Developmental Biology Center, Department of Pediatrics, The University of Minnesota, Minneapolis, Minnesota, United States of America
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Yi Ren
- The Developmental Biology Center, Department of Pediatrics, The University of Minnesota, Minneapolis, Minnesota, United States of America
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Katie A. Howe
- The Developmental Biology Center, Department of Pediatrics, The University of Minnesota, Minneapolis, Minnesota, United States of America
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Andrew M. Arsham
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Mathew C. Easterday
- The Developmental Biology Center, Department of Pediatrics, The University of Minnesota, Minneapolis, Minnesota, United States of America
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Thomas P. Neufeld
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Michael B. O'Connor
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Scott B. Selleck
- The Developmental Biology Center, Department of Pediatrics, The University of Minnesota, Minneapolis, Minnesota, United States of America
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
- * To whom correspondence should be addressed. E-mail:
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Gasic GP, Barco A, Avila J, Lerma J. A meeting to remember: meeting on memory and related disorders. EMBO Rep 2006; 7:768-73. [PMID: 16845373 PMCID: PMC1525152 DOI: 10.1038/sj.embor.7400746] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2006] [Accepted: 05/23/2006] [Indexed: 02/07/2023] Open
Affiliation(s)
- Gregory P Gasic
- Harvard Medical School and Massachussets General Hospital, Boston, Massachusetts 02115, USA.
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17
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Chen BE, Kondo M, Garnier A, Watson FL, Püettmann-Holgado R, Lamar DR, Schmucker D. The Molecular Diversity of Dscam Is Functionally Required for Neuronal Wiring Specificity in Drosophila. Cell 2006; 125:607-20. [PMID: 16678102 DOI: 10.1016/j.cell.2006.03.034] [Citation(s) in RCA: 144] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2006] [Revised: 03/19/2006] [Accepted: 03/29/2006] [Indexed: 11/28/2022]
Abstract
Alternative splicing of Dscam generates an enormous molecular diversity with maximally 38,016 different receptors. Whether this large diversity is required in vivo is currently unclear. We examined the role of Dscam in neuron-target recognition of single mechanosensory neurons, which connect with different target cells through multiple axonal branches. Analysis of Dscam null neurons demonstrated an essential role of Dscam for growth and directed extension of axon branches. Expression of randomly chosen single isoforms could not rescue connectivity but did restore basic axonal extension and rudimentary branching. Moreover, two Dscam alleles were generated that each reduced the maximally possible Dscam diversity to 22,176 isoforms. Reduction of Dscam diversity resulted in specific connectivity defects of mechanosensory neurons. Furthermore, the observed allele-specific phenotypes suggest functional differences among isoforms. Our findings provide evidence that a very large number of structurally unique receptor isoforms is required to ensure fidelity and precision of neuronal connectivity.
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Affiliation(s)
- Brian E Chen
- Department of Cancer Biology, Dana-Farber Cancer Institute, Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
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18
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Abstract
Affecting 1-3% of the population, mental retardation (MR) poses significant challenges for clinicians and scientists. Understanding the biology of MR is complicated by the extraordinary heterogeneity of genetic MR disorders. Detailed analyses of >1000 Online Mendelian Inheritance in Man (OMIM) database entries and literature searches through September 2003 revealed 282 molecularly identified MR genes. We estimate that hundreds more MR genes remain to be identified. A novel test, in which we distributed unmapped MR disorders proportionately across the autosomes, failed to eliminate the well-known X-chromosome overrepresentation of MR genes and candidate genes. This evidence argues against ascertainment bias as the main cause of the skewed distribution. On the basis of a synthesis of clinical and laboratory data, we developed a biological functions classification scheme for MR genes. Metabolic pathways, signaling pathways, and transcription are the most common functions, but numerous other aspects of neuronal and glial biology are controlled by MR genes as well. Using protein sequence and domain-organization comparisons, we found a striking conservation of MR genes and genetic pathways across the approximately 700 million years that separate Homo sapiens and Drosophila melanogaster. Eighty-seven percent have one or more fruit fly homologs and 76% have at least one candidate functional ortholog. We propose that D. melanogaster can be used in a systematic manner to study MR and possibly to develop bioassays for therapeutic drug discovery. We selected 42 Drosophila orthologs as most likely to reveal molecular and cellular mechanisms of nervous system development or plasticity relevant to MR.
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Affiliation(s)
- Jennifer K Inlow
- Arizona Research Laboratories Division of Neurobiology, University of Arizona, Tucson 85721-0077, USA
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19
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Abstract
Abstract
Affecting 1-3% of the population, mental retardation (MR) poses significant challenges for clinicians and scientists. Understanding the biology of MR is complicated by the extraordinary heterogeneity of genetic MR disorders. Detailed analyses of >1000 Online Mendelian Inheritance in Man (OMIM) database entries and literature searches through September 2003 revealed 282 molecularly identified MR genes. We estimate that hundreds more MR genes remain to be identified. A novel test, in which we distributed unmapped MR disorders proportionately across the autosomes, failed to eliminate the well-known X-chromosome overrepresentation of MR genes and candidate genes. This evidence argues against ascertainment bias as the main cause of the skewed distribution. On the basis of a synthesis of clinical and laboratory data, we developed a biological functions classification scheme for MR genes. Metabolic pathways, signaling pathways, and transcription are the most common functions, but numerous other aspects of neuronal and glial biology are controlled by MR genes as well. Using protein sequence and domain-organization comparisons, we found a striking conservation of MR genes and genetic pathways across the ∼700 million years that separate Homo sapiens and Drosophila melanogaster. Eighty-seven percent have one or more fruit fly homologs and 76% have at least one candidate functional ortholog. We propose that D. melanogaster can be used in a systematic manner to study MR and possibly to develop bioassays for therapeutic drug discovery. We selected 42 Drosophila orthologs as most likely to reveal molecular and cellular mechanisms of nervous system development or plasticity relevant to MR.
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Affiliation(s)
- Jennifer K Inlow
- Arizona Research Laboratories Division of Neurobiology, University of Arizona, Tucson, Arizona 85721-0077
| | - Linda L Restifo
- Arizona Research Laboratories Division of Neurobiology, University of Arizona, Tucson, Arizona 85721-0077
- Department of Neurology, University of Arizona, Tucson, Arizona 85721-0077
- Genetics Graduate Interdisciplinary Program, University of Arizona, Tucson, Arizona 85721-0077
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20
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Goberdhan DCI, Wilson C. PTEN: tumour suppressor, multifunctional growth regulator and more. Hum Mol Genet 2003; 12 Spec No 2:R239-48. [PMID: 12928488 DOI: 10.1093/hmg/ddg288] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The tumour suppressor gene PTEN is mutated in a wide range of human cancers at a frequency roughly comparable with p53. In addition, germline PTEN mutations are associated with several dominant growth disorders. The molecular and cellular basis of these disorders has been elucidated by detailed in vivo genetic analysis in model organisms, in particular the fruit fly and mouse. Studies in the fly have shown that PTEN's growth regulatory functions are primarily mediated via its lipid phosphatase activity, which specifically reduces the cellular levels of phosphatidylinositol 3,4,5-trisphosphate. This activity antagonizes the effects of activated PI3-kinase in the nutritionally controlled insulin receptor pathway, thereby reducing protein synthesis and restraining cell and organismal growth, while also regulating other biological processes, such as fertility and ageing. Remarkably, this range of functions appears to be conserved in all higher organisms. PTEN also plays a role as a specialized cytoskeletal regulator, which, for example, is involved in directional movement of some migratory cells and may be important in metastasis. Furthermore, conditional knockouts in the mouse have recently revealed functions for PTEN in other processes, such as cell type specification and cardiac muscle contractility. Genetic approaches have therefore revealed a surprising diversity of global and cell type-specific PTEN-regulated functions that appear to be primarily controlled by modulation of a single phosphoinositide. Together with evidence from studies in cell culture that suggests links between PTEN and other growth regulatory genes such as p53, these studies provide new insights into PTEN-linked disorders and are beginning to suggest potential clinical strategies to combat these and other diseases.
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21
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Abstract
Mammalian insulin and insulin-like growth factors (IGFs) signal through several receptors with different ligand specificities to regulate metabolism and growth. This regulation is defective in diabetes and in a wide variety of human tumors. Recent analysis in Drosophila melanogaster has revealed that insulin-like molecules (known as DILPs in flies) also control growth and metabolism, but probably do so by signaling through a single insulin receptor (InR). The intracellular signaling molecules regulated by this receptor are highly evolutionarily conserved. Work in flies has helped to dissect the network of InR-regulated intracellular signaling pathways and identify some of the critical players in these pathways and in interacting signaling cascades. Surprisingly, these studies have shown that DILPs control tissue and body growth primarily by regulating cell growth and cell size. Changes in cell growth produced by these molecules may subsequently modulate the rate of cell proliferation in a cell type-specific fashion. At least part of this growth effect is mediated by two small groups of neurons in the Drosophila brain, which secrete DILPs into the circulatory system at levels that are modulated by nutrition. This signaling center is also involved in DILP-dependent control of the fly's rate of development, fertility, and life span. These surprisingly diverse functions of InR signaling, which appear to be conserved in all higher animals, reflect a central role for this pathway in coordinating development, physiology, and properly proportioned growth of the organism in response to its nutritional state. Studies in flies are providing important new insights into the biology of this system, and the identification of novel components in the InR-regulated signaling cascade is already beginning to inform the development of new therapeutic strategies for insulin-linked diseases in the clinic.
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Affiliation(s)
- Deborah C I Goberdhan
- Department of Human Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX, United Kingdom
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22
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Gianola S, Savio T, Schwab ME, Rossi F. Cell-autonomous mechanisms and myelin-associated factors contribute to the development of Purkinje axon intracortical plexus in the rat cerebellum. J Neurosci 2003; 23:4613-24. [PMID: 12805301 PMCID: PMC6740793] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/03/2023] Open
Abstract
The highly specific connection patterns of the mature CNS are shaped through finely regulated processes of axon growth and retraction. To investigate the relative contribution of cell-autonomous mechanisms and extrinsic cues in these events, we examined the development of Purkinje axon intracortical plexus in the rat cerebellum. During the first postnatal week, several new processes sprout from focal swellings along the initial portion of the Purkinje neurite and spread in the granular layer. Intense structural plasticity occurs during the following week, with pruning of collateral branches and remodeling of terminal arbors. The mature distribution of the Purkinje infraganglionic plexus, confined within the most superficial portion of the granular layer, is attained at approximately postnatal day 15. A similar neuritic branching pattern is also developed by Purkinje cells grown in cultures of dissociated cerebellar cells or transplanted to extracerebellar CNS regions, suggesting that cell-autonomous mechanisms contribute to determining the Purkinje axon phenotype. The structural remodeling of Purkinje intracortical plexus is concomitant with the development of cerebellar myelin. To ask whether myelin-associated factors contribute to the morphological maturation of Purkinje neurites, we prevented normal myelinogenesis by killing oligodendrocyte precursors with 5'-azacytidine or by applying neutralizing antibodies against the myelin-associated neurite growth inhibitor Nogo-A. In both conditions, Purkinje axons retained exuberant branches, and the terminal plexus spanned the entire extent of the granular layer. Thus, the formation of Purkinje axon collaterals is, in part, controlled by intrinsic determinants, but their growth and distribution are regulated by environmental signals, among which are myelin-derived cues.
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Affiliation(s)
- Sara Gianola
- Department of Neuroscience, Rita Levi Montalcini Centre for Brain Repair, University of Turin, I-10125 Turin, Italy
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Radimerski T, Montagne J, Hemmings-Mieszczak M, Thomas G. Lethality of Drosophila lacking TSC tumor suppressor function rescued by reducing dS6K signaling. Genes Dev 2002; 16:2627-32. [PMID: 12381661 PMCID: PMC187466 DOI: 10.1101/gad.239102] [Citation(s) in RCA: 157] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Tuberous sclerosis complex (TSC) is a genetic disorder caused by mutations in one of two tumor suppressor genes, TSC1 and TSC2. Here, we show that absence of Drosophila Tsc1/2 leads to constitutive dS6K activation and inhibition of dPKB, the latter effect being relieved by loss of dS6K. In contrast, the dPTEN tumor suppressor, a negative effector of PI3K, has little effect on dS6K, but negatively regulates dPKB. More importantly, we demonstrate that reducing dS6K signaling rescues early larval lethality associated with loss of dTsc1/2 function, arguing that the S6K pathway is a promising target for the treatment of TSC.
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Affiliation(s)
- Thomas Radimerski
- Friedrich Miescher Institute for Biomedical Research, CH-4058, Basel, Switzerland
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Acebes A, Ferrús A. Increasing the number of synapses modifies olfactory perception in Drosophila. J Neurosci 2001; 21:6264-73. [PMID: 11487649 PMCID: PMC6763191] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/21/2023] Open
Abstract
The Drosophila mutant gigas produces an enlargement of postmitotic cells caused by additional rounds of DNA replication. In neurons, the mutant cell establishes more synapses than normal. We have taken advantage of this feature to study the effect of synapse number on odorant perception. Mosaic adults were generated in which one antenna was homozygous for gigas, whereas the contralateral side served as an internal control. Morphological analysis indicates that the number and type of sensory afferents forming the mutant antenna, as well as their projection to the olfactory glomeruli, are normal. In contrast, the volume of identified glomeruli increases to a variable extent, and mutant sensory neurons branch profusely. The number of synapses, estimated in the ventral (V) glomerulus that receives ipsilateral afferents only, is increased twofold to threefold. Large-dense-core vesicle-containing terminals that probably modulate olfactory centers are identified in the V glomerulus. Their number and size are not modified by the mutant input. Sensory transduction, measured by electroantennograms, is normal in amplitude and kinetics. In odorant tests, however, the profile of the behavioral response to ethyl acetate shows attractive responses to concentrations to which sibling controls remain indifferent (10(-)8 and 10(-)7 v/v). In addition, the intensity of the response is augmented both at attractive and repulsive odorant concentrations with respect to that of controls. These results demonstrate that increased synapse number in the sensory neurons can modify the behavior of the organism, allowing a higher sensitivity of perception.
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Affiliation(s)
- A Acebes
- Instituto Cajal, Consejo Superior de Investigaciones Cientificas, Madrid E-28002, Spain
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25
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Abstract
Neural geometry is the major factor that determines connectivity and, possibly, functional output from a nervous system. Recently some of the proteins and pathways involved in specific modes of branch formation or maintenance, or both, have been described. To a variable extent, dendrites and axon collaterals can be viewed as dynamic structures subject to fine modulation that can result either in further growth or retraction. Each form of branching results from specific molecular mechanisms. Cell-internal, substrate-derived factors and functional activity, however, can often differ in their effect according to cell type and physiological context at the site of branch formation. Neural branching is not a linear process but an integrative one that takes place in a microenvironment where we have only a limited experimental access. To attain a coherent mechanism for this phenomenon, quantitative in situ data on the proteins involved and their interactions will be required.
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Affiliation(s)
- A Acebes
- The Instituto Cajal (CSIC), 28002, Madrid, Spain
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26
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Prokop A, Uhler J, Roote J, Bate M. The kakapo mutation affects terminal arborization and central dendritic sprouting of Drosophila motorneurons. J Cell Biol 1998; 143:1283-94. [PMID: 9832556 PMCID: PMC2133088 DOI: 10.1083/jcb.143.5.1283] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/1998] [Revised: 09/14/1998] [Indexed: 11/22/2022] Open
Abstract
The lethal mutation l(2)CA4 causes specific defects in local growth of neuronal processes. We uncovered four alleles of l(2)CA4 and mapped it to bands 50A-C on the polytene chromosomes and found it to be allelic to kakapo (. Genetics. 146:275- 285). In embryos carrying our kakapo mutant alleles, motorneurons form correct nerve branches, showing that long distance growth of neuronal processes is unaffected. However, neuromuscular junctions (NMJs) fail to form normal local arbors on their target muscles and are significantly reduced in size. In agreement with this finding, antibodies against kakapo (Gregory and Brown. 1998. J. Cell Biol. 143:1271-1282) detect a specific epitope at all or most Drosophila NMJs. Within the central nervous system of kakapo mutant embryos, neuronal dendrites of the RP3 motorneuron form at correct positions, but are significantly reduced in size. At the subcellular level we demonstrate two phenotypes potentially responsible for the defects in neuronal branching: first, transmembrane proteins, which can play important roles in neuronal growth regulation, are incorrectly localized along neuronal processes. Second, microtubules play an important role in neuronal growth, and kakapo appears to be required for their organization in certain ectodermal cells: On the one hand, kakapo mutant embryos exhibit impaired microtubule organization within epidermal cells leading to detachment of muscles from the cuticle. On the other, a specific type of sensory neuron (scolopidial neurons) shows defects in microtubule organization and detaches from its support cells.
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Affiliation(s)
- A Prokop
- Department of Zoology, University of Cambridge, Cambridge CB2 3EH, United Kingdom.
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