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Carranza A, Howard LJ, Brown HE, Ametepe AS, Evans TA. Slit-independent guidance of longitudinal axons by Drosophila Robo3. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.08.539901. [PMID: 37214810 PMCID: PMC10197545 DOI: 10.1101/2023.05.08.539901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Drosophila Robo3 is a member of the evolutionarily conserved Roundabout (Robo) receptor family and one of three Drosophila Robo paralogs. During embryonic ventral nerve cord development, Robo3 does not participate in canonical Slit-dependent midline repulsion, but instead regulates the formation of longitudinal axon pathways at specific positions along the medial-lateral axis. Longitudinal axon guidance by Robo3 is hypothesized to be Slit dependent, but this has not been directly tested. Here we create a series of Robo3 variants in which the N-terminal Ig1 domain is deleted or modified, in order to characterize the functional importance of Ig1 and Slit binding for Robo3's axon guidance activity. We show that Robo3 requires its Ig1 domain for interaction with Slit and for proper axonal localization in embryonic neurons, but deleting Ig1 from Robo3 only partially disrupts longitudinal pathway formation. Robo3 variants with modified Ig1 domains that cannot bind Slit retain proper localization and fully rescue longitudinal axon guidance. Our results indicate that Robo3 guides longitudinal axons independently of Slit, and that sequences both within and outside of Ig1 contribute to this Slit-independent activity.
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Affiliation(s)
- Abigail Carranza
- Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701
- Current Address: Texas A&M University School of Medicine, Bryan, TX 77807
| | - LaFreda J. Howard
- Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701
- Current Address: NAVA PBC, Washington, DC 20005
| | - Haley E. Brown
- Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701
- Current Address: Department of Biology, Indiana University, Bloomington, IN 47405, USA
| | | | - Timothy A. Evans
- Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701
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2
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Huang Y, Ma M, Mao X, Pehlivan D, Kanca O, Un-Candan F, Shu L, Akay G, Mitani T, Lu S, Candan S, Wang H, Xiao B, Lupski JR, Bellen HJ. Novel dominant and recessive variants in human ROBO1 cause distinct neurodevelopmental defects through different mechanisms. Hum Mol Genet 2022; 31:2751-2765. [PMID: 35348658 PMCID: PMC9402236 DOI: 10.1093/hmg/ddac070] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 03/17/2022] [Accepted: 03/20/2022] [Indexed: 07/27/2023] Open
Abstract
The Roundabout (Robo) receptors, located on growth cones of neurons, induce axon repulsion in response to the extracellular ligand Slit. The Robo family of proteins controls midline crossing of commissural neurons during development in flies. Mono- and bi-allelic variants in human ROBO1 (HGNC: 10249) have been associated with incomplete penetrance and variable expressivity for a breath of phenotypes, including neurodevelopmental defects such as strabismus, pituitary defects, intellectual impairment, as well as defects in heart and kidney. Here, we report two novel ROBO1 variants associated with very distinct phenotypes. A homozygous missense p.S1522L variant in three affected siblings with nystagmus; and a monoallelic de novo p.D422G variant in a proband who presented with early-onset epileptic encephalopathy. We modeled these variants in Drosophila and first generated a null allele by inserting a CRIMIC T2A-GAL4 in an intron. Flies that lack robo1 exhibit reduced viability but have very severe midline crossing defects in the central nervous system. The fly wild-type cDNA driven by T2A-Gal4 partially rescues both defects. Overexpression of the human reference ROBO1 with T2A-GAL4 is toxic and reduces viability, whereas the recessive p.S1522L variant is less toxic, suggesting that it is a partial loss-of-function allele. In contrast, the dominant variant in fly robo1 (p.D413G) affects protein localization, impairs axonal guidance activity and induces mild phototransduction defects, suggesting that it is a neomorphic allele. In summary, our studies expand the phenotypic spectrum associated with ROBO1 variant alleles.
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Affiliation(s)
- Yan Huang
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Baylor College of Medicine, Houston, TX 77030, USA
| | - Mengqi Ma
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Baylor College of Medicine, Houston, TX 77030, USA
| | - Xiao Mao
- National Health Commission Key Laboratory for Birth Defect Research and Prevention, Hunan Provincial Maternal and Child Health Care Hospital, Changsha, Hunan 410008, China
- Department of Medical Genetics, Maternal and Child Health Hospital of Hunan Province, Changsha, Hunan 410008, China
| | - Davut Pehlivan
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
- Division of Neurology and Developmental Neuroscience, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA
- Texas Children’s Hospital, Houston, TX 77030, USA
| | - Oguz Kanca
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Baylor College of Medicine, Houston, TX 77030, USA
| | - Feride Un-Candan
- Department of Neuroloy, Balikesir Ataturk Public Hospital, Balikesir 10100, Turkey
| | - Li Shu
- National Health Commission Key Laboratory for Birth Defect Research and Prevention, Hunan Provincial Maternal and Child Health Care Hospital, Changsha, Hunan 410008, China
- Department of Medical Genetics, Maternal and Child Health Hospital of Hunan Province, Changsha, Hunan 410008, China
| | - Gulsen Akay
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Tadahiro Mitani
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Shenzhao Lu
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Baylor College of Medicine, Houston, TX 77030, USA
| | - Sukru Candan
- Department of Medical Genetics, Balikesir Ataturk Public Hospital, Balikesir 10100, Turkey
| | - Hua Wang
- National Health Commission Key Laboratory for Birth Defect Research and Prevention, Hunan Provincial Maternal and Child Health Care Hospital, Changsha, Hunan 410008, China
- Department of Medical Genetics, Maternal and Child Health Hospital of Hunan Province, Changsha, Hunan 410008, China
| | - Bo Xiao
- Neurology Department, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China
| | - James R Lupski
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
- Texas Children’s Hospital, Houston, TX 77030, USA
| | - Hugo J Bellen
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Baylor College of Medicine, Houston, TX 77030, USA
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3
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Scapin G, Gasparotto M, Peterle D, Tescari S, Porcellato E, Piovesan A, Righetto I, Acquasaliente L, De Filippis V, Filippini F. A conserved Neurite Outgrowth and Guidance motif with biomimetic potential in neuronal Cell Adhesion Molecules. Comput Struct Biotechnol J 2021; 19:5622-5636. [PMID: 34712402 PMCID: PMC8529090 DOI: 10.1016/j.csbj.2021.10.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 09/27/2021] [Accepted: 10/03/2021] [Indexed: 01/02/2023] Open
Abstract
The discovery of conserved protein motifs can, in turn, unveil important regulatory signals, and when properly designed, synthetic peptides derived from such motifs can be used as biomimetics for biotechnological and therapeutic purposes. We report here that specific Ig-like repeats from the extracellular domains of neuronal Cell Adhesion Molecules share a highly conserved Neurite Outgrowth and Guidance (NOG) motif, which mediates homo- and heterophilic interactions crucial in neural development and repair. Synthetic peptides derived from the NOG motif of such proteins can boost neuritogenesis, and this potential is also retained by peptides with recombinant sequences, when fitting the NOG sequence pattern. The NOG motif discovery not only provides one more tile to the complex puzzle of neuritogenesis, but also opens the route to new neural regeneration strategies via a tunable biomimetic toolbox.
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Affiliation(s)
- Giorgia Scapin
- Synthetic Biology and Biotechnology Unit, Department of Biology, University of Padua, 35131, Italy
| | - Matteo Gasparotto
- Synthetic Biology and Biotechnology Unit, Department of Biology, University of Padua, 35131, Italy
| | - Daniele Peterle
- Department of Pharmaceutical and Pharmacological Sciences, University of Padua, 35131, Italy
| | - Simone Tescari
- Department of Pharmaceutical and Pharmacological Sciences, University of Padua, 35131, Italy
| | - Elena Porcellato
- Synthetic Biology and Biotechnology Unit, Department of Biology, University of Padua, 35131, Italy.,Department of Pharmaceutical and Pharmacological Sciences, University of Padua, 35131, Italy
| | - Alberto Piovesan
- Synthetic Biology and Biotechnology Unit, Department of Biology, University of Padua, 35131, Italy.,Department of Pharmaceutical and Pharmacological Sciences, University of Padua, 35131, Italy
| | - Irene Righetto
- Synthetic Biology and Biotechnology Unit, Department of Biology, University of Padua, 35131, Italy
| | - Laura Acquasaliente
- Department of Pharmaceutical and Pharmacological Sciences, University of Padua, 35131, Italy
| | - Vincenzo De Filippis
- Department of Pharmaceutical and Pharmacological Sciences, University of Padua, 35131, Italy
| | - Francesco Filippini
- Synthetic Biology and Biotechnology Unit, Department of Biology, University of Padua, 35131, Italy
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Howard LJ, Reichert MC, Evans TA. The Slit-binding Ig1 domain is required for multiple axon guidance activities of Drosophila Robo2. Genesis 2021; 59:e23443. [PMID: 34411419 PMCID: PMC8446337 DOI: 10.1002/dvg.23443] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2021] [Revised: 07/28/2021] [Accepted: 08/01/2021] [Indexed: 12/02/2022]
Abstract
Drosophila Robo2 is a member of the evolutionarily conserved Roundabout (Robo) family of axon guidance receptors. Robo receptors signal midline repulsion in response to Slit ligands, which bind to the N‐terminal Ig1 domain in most family members. In the Drosophila embryonic ventral nerve cord, Robo1 and Robo2 signal Slit‐dependent midline repulsion, while Robo2 also regulates the medial‐lateral position of longitudinal axon pathways and acts non‐autonomously to promote midline crossing of commissural axons. While Robo2 signals midline repulsion in response to Slit, it is less clear whether Robo2's other activities are also Slit‐dependent. To determine which of Robo2's axon guidance roles depend on its Slit‐binding Ig1 domain, we used a clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9‐based strategy to replace the endogenous robo2 gene with a robo2 variant lacking the Ig1 domain (robo2∆Ig1). We compare the expression and localization of Robo2∆Ig1 protein with full‐length Robo2 in embryonic neurons in vivo and examine its ability to substitute for Robo2 to mediate midline repulsion and lateral axon pathway formation. We find that the removal of the Ig1 domain from Robo2∆Ig1 disrupts both of these axon guidance activities. In addition, we find that the Ig1 domain of Robo2 is required for its proper subcellular localization in embryonic neurons, a role that is not shared by the Ig1 domain of Robo1. Finally, we report that although FasII‐positive lateral axons are misguided in embryos expressing Robo2∆Ig1, the axons that normally express Robo2 are correctly guided to the lateral zone, suggesting that Robo2 may guide lateral longitudinal axons through a cell non‐autonomous mechanism.
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Affiliation(s)
- LaFreda J Howard
- Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas, USA.,City of Houston Health Department, University of Arkansas, Houston, Texas, USA
| | - Marie C Reichert
- Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas, USA
| | - Timothy A Evans
- Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas, USA
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Daiber T, VanderZwan-Butler CJ, Bashaw GJ, Evans TA. Conserved and divergent aspects of Robo receptor signaling and regulation between Drosophila Robo1 and C. elegans SAX-3. Genetics 2021; 217:iyab018. [PMID: 33789352 PMCID: PMC8045725 DOI: 10.1093/genetics/iyab018] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Accepted: 01/28/2021] [Indexed: 11/24/2022] Open
Abstract
The evolutionarily conserved Roundabout (Robo) family of axon guidance receptors control midline crossing of axons in response to the midline repellant ligand Slit in bilaterian animals including insects, nematodes, and vertebrates. Despite this strong evolutionary conservation, it is unclear whether the signaling mechanism(s) downstream of Robo receptors are similarly conserved. To directly compare midline repulsive signaling in Robo family members from different species, here we use a transgenic approach to express the Robo family receptor SAX-3 from the nematode Caenorhabditis elegans in neurons of the fruit fly, Drosophila melanogaster. We examine SAX-3's ability to repel Drosophila axons from the Slit-expressing midline in gain of function assays, and test SAX-3's ability to substitute for Drosophila Robo1 during fly embryonic development in genetic rescue experiments. We show that C. elegans SAX-3 is properly translated and localized to neuronal axons when expressed in the Drosophila embryonic CNS, and that SAX-3 can signal midline repulsion in Drosophila embryonic neurons, although not as efficiently as Drosophila Robo1. Using a series of Robo1/SAX-3 chimeras, we show that the SAX-3 cytoplasmic domain can signal midline repulsion to the same extent as Robo1 when combined with the Robo1 ectodomain. We show that SAX-3 is not subject to endosomal sorting by the negative regulator Commissureless (Comm) in Drosophila neurons in vivo, and that peri-membrane and ectodomain sequences are both required for Comm sorting of Drosophila Robo1.
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Affiliation(s)
- Trent Daiber
- Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701, USA
| | | | - Greg J Bashaw
- Department of Neuroscience, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Timothy A Evans
- Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701, USA
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Brown HE, Evans TA. Minimal structural elements required for midline repulsive signaling and regulation of Drosophila Robo1. PLoS One 2020; 15:e0241150. [PMID: 33091076 PMCID: PMC7580999 DOI: 10.1371/journal.pone.0241150] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Accepted: 10/08/2020] [Indexed: 02/07/2023] Open
Abstract
The Roundabout (Robo) family of axon guidance receptors has a conserved ectodomain arrangement of five immunoglobulin-like (Ig) domains plus three fibronectin type III (Fn) repeats. Based on the strong evolutionary conservation of this domain structure among Robo receptors, as well as in vitro structural and domain-domain interaction studies of Robo family members, this ectodomain arrangement is predicted to be important for Robo receptor signaling in response to Slit ligands. Here, we define the minimal ectodomain structure required for Slit binding and midline repulsive signaling in vivo by Drosophila Robo1. We find that the majority of the Robo1 ectodomain is dispensable for both Slit binding and repulsive signaling. We show that a significant level of midline repulsive signaling activity is retained when all Robo1 ectodomain elements apart from Ig1 are deleted, and that the combination of Ig1 plus one additional ectodomain element (Ig2, Ig5, or Fn3) is sufficient to restore midline repulsion to wild type levels. Further, we find that deleting four out of five Robo1 Ig domains (ΔIg2-5) does not affect negative regulation of Robo1 by Commissureless (Comm) or Robo2, while variants lacking all three fibronectin repeats (ΔFn1-3 and ΔIg2-Fn3) are insensitive to regulation by both Comm and Robo2, signifying a novel regulatory role for Robo1's Fn repeats. Our results provide an in vivo perspective on the importance of the conserved 5+3 ectodomain structure of Robo receptors, and suggest that specific biochemical properties and/or ectodomain structural conformations observed in vitro for domains other than Ig1 may have limited significance for in vivo signaling in the context of midline repulsion.
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Affiliation(s)
- Haley E. Brown
- Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas, United States of America
| | - Timothy A. Evans
- Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas, United States of America
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Zhao Y, Yang JY, Thieker DF, Xu Y, Zong C, Boons GJ, Liu J, Woods RJ, Moremen KW, Amster IJ. A Traveling Wave Ion Mobility Spectrometry (TWIMS) Study of the Robo1-Heparan Sulfate Interaction. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2018; 29:1153-1165. [PMID: 29520710 PMCID: PMC6004239 DOI: 10.1007/s13361-018-1903-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2017] [Revised: 01/14/2018] [Accepted: 01/14/2018] [Indexed: 06/10/2023]
Abstract
Roundabout 1 (Robo1) interacts with its receptor Slit to regulate axon guidance, axon branching, and dendritic development in the nervous system and to regulate morphogenesis and many cell functions in the nonneuronal tissues. This interaction is known to be critically regulated by heparan sulfate (HS). Previous studies suggest that HS is required to promote the binding of Robo1 to Slit to form the minimal signaling complex, but the molecular details and the structural requirements of HS for this interaction are still unclear. Here, we describe the application of traveling wave ion mobility spectrometry (TWIMS) to study the conformational details of the Robo1-HS interaction. The results suggest that Robo1 exists in two conformations that differ by their compactness and capability to interact with HS. The results also suggest that the highly flexible interdomain hinge region connecting the Ig1 and Ig2 domains of Robo1 plays an important functional role in promoting the Robo1-Slit interaction. Moreover, variations in the sulfation pattern and size of HS were found to affect its binding affinity and selectivity to interact with different conformations of Robo1. Both MS measurements and CIU experiments show that the Robo1-HS interaction requires the presence of a specific size and pattern of modification of HS. Furthermore, the effect of N-glycosylation on the conformation of Robo1 and its binding modes with HS is reported. Graphical Abstract ᅟ.
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Affiliation(s)
- Yuejie Zhao
- Department of Chemistry, University of Georgia, Athens, GA, 30602, USA
| | - Jeong Yeh Yang
- Complex Carbohydrate Research Center, University of Georgia, Athens, GA, 30602, USA
| | - David F Thieker
- Complex Carbohydrate Research Center, University of Georgia, Athens, GA, 30602, USA
| | - Yongmei Xu
- Eshelman School of Pharmacy, Division of Chemical Biology & Medicinal Chemistry, University of North Carolina, Chapel Hill, NC, USA
| | - Chengli Zong
- Complex Carbohydrate Research Center, University of Georgia, Athens, GA, 30602, USA
| | - Geert-Jan Boons
- Complex Carbohydrate Research Center, University of Georgia, Athens, GA, 30602, USA
| | - Jian Liu
- Eshelman School of Pharmacy, Division of Chemical Biology & Medicinal Chemistry, University of North Carolina, Chapel Hill, NC, USA
| | - Robert J Woods
- Complex Carbohydrate Research Center, University of Georgia, Athens, GA, 30602, USA
| | - Kelley W Moremen
- Complex Carbohydrate Research Center, University of Georgia, Athens, GA, 30602, USA
| | - I Jonathan Amster
- Department of Chemistry, University of Georgia, Athens, GA, 30602, USA.
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Brown HE, Reichert MC, Evans TA. In Vivo Functional Analysis of Drosophila Robo1 Fibronectin Type-III Repeats. G3 (BETHESDA, MD.) 2018; 8:621-630. [PMID: 29217730 PMCID: PMC5919748 DOI: 10.1534/g3.117.300418] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Accepted: 12/05/2017] [Indexed: 12/02/2022]
Abstract
The repellant ligand Slit and its Roundabout (Robo) family receptors regulate midline crossing of axons during development of the embryonic central nervous system (CNS). Slit proteins are produced at the midline and signal through Robo receptors to repel axons from the midline. Disruption of Slit-Robo signaling causes ectopic midline-crossing phenotypes in the CNS of a broad range of animals, including insects and vertebrates. While previous studies have investigated the roles of Drosophila melanogaster Robo1's five Immunoglobulin-like (Ig) domains, little is known about the importance of the three evolutionarily conserved Fibronectin (Fn) type-III repeats. We have individually deleted each of Drosophila Robo1's three Fn repeats, and then tested these Robo1 variants in vitro to determine their ability to bind Slit in cultured Drosophila cells and in vivo to investigate the requirement for each domain in regulating Robo1's embryonic expression pattern, axonal localization, midline repulsive function, and sensitivity to Commissureless (Comm) downregulation. We demonstrate that the Fn repeats are not required for Robo1 to bind Slit or for proper expression of Robo1 in Drosophila embryonic neurons. When expressed in a robo1 mutant background, these variants are able to restore midline repulsion to an extent equivalent to full-length Robo1. We identify a novel requirement for Fn3 in the exclusion of Robo1 from commissures and downregulation of Robo1 by Comm. Our results indicate that each of the Drosophila Robo1 Fn repeats are individually dispensable for the protein's role in midline repulsion, despite the evolutionarily conserved "5 + 3" protein structure.
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Affiliation(s)
- Haley E Brown
- Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701
| | - Marie C Reichert
- Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701
| | - Timothy A Evans
- Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701
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9
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Howard LJ, Brown HE, Wadsworth BC, Evans TA. Midline axon guidance in the Drosophila embryonic central nervous system. Semin Cell Dev Biol 2017; 85:13-25. [PMID: 29174915 DOI: 10.1016/j.semcdb.2017.11.029] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Revised: 11/13/2017] [Accepted: 11/21/2017] [Indexed: 02/02/2023]
Abstract
Studies in the fruit fly Drosophila melanogaster have provided many fundamental insights into the genetic regulation of neural development, including the identification and characterization of evolutionarily conserved axon guidance pathways and their roles in important guidance decisions. Due to its highly organized and fast-developing embryonic nervous system, relatively small number of neurons, and molecular and genetic tools for identifying, labeling, and manipulating individual neurons or small neuronal subsets, studies of axon guidance in the Drosophila embryonic CNS have allowed researchers to dissect these genetic mechanisms with a high degree of precision. In this review, we discuss the major axon guidance pathways that regulate midline crossing of axons and the formation and guidance of longitudinal axon tracts, two processes that contribute to the development of the precise three-dimensional structure of the insect nerve cord. We focus particularly on recent insights into the roles and regulation of canonical midline axon guidance pathways, and on additional factors and pathways that have recently been shown to contribute to axon guidance decisions at and near the midline.
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Affiliation(s)
- LaFreda J Howard
- Department of Biological Sciences, University of Arkansas, Fayetteville AR 72701, USA
| | - Haley E Brown
- Department of Biological Sciences, University of Arkansas, Fayetteville AR 72701, USA
| | - Benjamin C Wadsworth
- Department of Biological Sciences, University of Arkansas, Fayetteville AR 72701, USA
| | - Timothy A Evans
- Department of Biological Sciences, University of Arkansas, Fayetteville AR 72701, USA.
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