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Peter G Fuerst - One of the best experts on this subject based on the ideXlab platform.
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Expression patterns of DSCAM and sdk gene paralogs in developing zebrafish retina.
Molecular vision, 2018Co-Authors: Carlos A. Galicia, Joshua M. Sukeena, Deborah L. Stenkamp, Peter G FuerstAbstract:Purpose The differential adhesion hypothesis states that a cell adhesion code provides cues that direct the specificity of nervous system development. The Down syndrome cell adhesion molecule (DSCAM) and sidekick (SDK) proteins belong to the immunoglobulin superfamily of cell adhesion molecules (CAMs) and provide both attractive and repulsive cues that help to organize the nervous system during development, according to the differential adhesion hypothesis. The zebrafish genome is enriched in DSCAM and sdk genes, making the zebrafish an excellent model system to further test this hypothesis. The goal of this study is to describe the phylogenetic relationships of the paralogous CAM genes and their spatial expression and co-expression patterns in the embryonic zebrafish retina. Methods Exon-intron structures, karyotypic locations, genomic context, and amino acid sequences of the zebrafish CAM genes (DSCAMa, DSCAMb, DSCAMl1, sdk1a, sdk1b, sdk2a, and sdk2b) were obtained from the Ensembl genome database. The Prosite and SMART programs were used to determine the number and identity of protein domains for each CAM gene. The randomized axelerated maximum likelihood (RaxML) program was used to perform a phylogenetic analysis of the zebrafish CAM genes and orthologs in other vertebrates. A synteny analysis of regions surrounding zebrafish CAM paralogs was performed. Digoxigenin (dig)-labeled cRNA probes for each CAM gene were generated to perform in situ hybridization of retinal cryosections from zebrafish embryos and larvae. Dual in situ hybridization of retinal cryosections from zebrafish larvae was performed with dig- and fluorescein-labeled cRNA probes. Results We found the studied zebrafish CAM genes encode similar protein domain structures as their corresponding orthologs in mammals and possess similar intron-exon organizations. CAM paralogs were located on different chromosomes. Phylogenetic and synteny analyses provided support for zebrafish DSCAM and sdk2 paralogs having originated during the teleost genome duplication. We found that DSCAMa and DSCAMb are co-expressed in the ganglion cell layer (GCL) and the basal portion of the inner nuclear layer (INL), with weak expression in the photoreceptor-containing outer nuclear layer (ONL). Of the DSCAM genes, only DSCAMb was strongly expressed in ONL. Sdk1a and sdk1b were co-expressed in the GCL and the basal portion of the INL. Sdk2a and sdk2b also showed co-expression in the GCL and basal portion of the INL. All Sdk genes were expressed in the ciliary marginal zone (CMZ). Dual in situ hybridizations revealed alternating patterns of co-expression and exclusive expression for the DSCAM and sdk1 paralogs in cells of the GCL and the INL. The same alternating pattern was observed between DSCAM and sdk2 paralogs and between sdk1 and sdk2 paralogs. The expression of DSCAMl1 was observed in the INL and the GCL, with some cells in the basal portion of the INL showing co-expression of DSCAMl1 and DSCAMa. Conclusions These findings suggest that zebrafish DSCAM and sdk2 paralogs were likely the result of the teleost whole genome duplication and that all CAM duplicates show some differential expression patterns. We also demonstrate that the comparative expression patterns of CAM genes in the zebrafish are distinct from the exclusive expression patterns observed in chick retina, in which retinal ganglion cells express one of the four chick DSCAM or Sdk genes only. The patterns in zebrafish are more similar to those of mice, in which co-expression of DSCAM and Sdk genes is observed. These findings provide the groundwork for future functional analysis of the roles of the CAM paralogs in zebrafish.
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DSCAM promotes axon fasciculation and growth in the developing optic pathway
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Freyja Bruce, Peter G Fuerst, Samantha Brown, Jonathan N Smith, Lynda ErskineAbstract:Although many aspects of optic pathway development are beginning to be understood, the mechanisms promoting the growth of retinal ganglion cell (RGC) axons toward visual targets remain largely unknown. Down syndrome cell adhesion molecule (DSCAM) is expressed by mouse RGCs shortly after they differentiate at embryonic day 12 and is essential for multiple aspects of postnatal visual system development. Here we show that DSCAM is also required during embryonic development for the fasciculation and growth of RGC axons. DSCAM is expressed along the developing optic pathway in a pattern consistent with a role in regulating RGC axon outgrowth. In mice carrying spontaneous mutations in DSCAM (DSCAMdel17 ; DSCAM2J), RGC axons pathfind normally, but growth from the chiasm toward their targets is impaired, resulting in a delay in RGC axons reaching the dorsal thalamus compared with that seen in wild-type littermates. Conversely, DSCAM gain of function results in exuberant growth into the dorsal thalamus. The growth of ipsilaterally projecting axons is particularly affected. Axon organization in the optic chiasm and tract and RGC growth cone morphologies are also altered in DSCAM mutants. In vitro DSCAM promotes RGC axon growth and fasciculation, and can act independently of cell contact. In vitro and in situ DSCAM is required both in the RGC axons and in their environment for the promotion of axon outgrowth, consistent with a homotypic mode of action. These findings identify DSCAM as a permissive signal that promotes the growth and fasciculation of RGC axons, controlling the timing of when RGC axons reach their targets.
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replacing the pdz interacting c termini of DSCAM and DSCAMl1 with epitope tags causes different phenotypic severity in different cell populations
eLife, 2016Co-Authors: Andrew M Garrett, Peter G Fuerst, Abigail L D Tadenev, Yuna T Hammond, Robert W BurgessAbstract:Neurons in a part of the eye called the retina detect light and convert it into electrical signals that are sent to the brain. Different types of neurons in the retina are arranged vertically into layers and horizontally in a mosaic pattern so that two neurons of the same type are not next to each other. To establish this highly organized pattern, neurons in the developing retina must be able to recognize other neurons of the same type and avoid moving towards them – a process referred to as self-avoidance. A group of proteins called the DSCAMs are found on the surface of neurons and play key roles in positioning them in the retina. DSCAMs promote self-avoidance, help to establish connections between certain neurons and kill any excess neurons that are not needed. However, the mechanisms by which DSCAMs serve these three roles were not known. Scaffolding proteins in the cell interior interact with DSCAMs to hold them in place on the cell surface. Garrett et al. investigated whether DSCAMs need to interact with the scaffolding proteins in order to carry out any of their activities. The experiments used mice that had been genetically engineered to produce mutant DSCAM proteins that cannot bind to the scaffolding proteins. Garrett et al. hypothesized that this would affect the activities of DSCAMs in all of the different types of neurons in the retina. However, the experiments show that the mutant DSCAM proteins had different effects on the neurons. Some types of neurons developed normally, while others experienced disruptions in all three of the processes that DSCAMs are normally involved in. Some other neurons were affected to a moderate extent. This indicates that DSCAMs use different mechanisms in different types of neurons to carry out the same activities. The next step is to find out what other proteins DSCAMs need to interact with in different types of neurons.
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Novel axon projection after stress and degeneration in the DSCAM mutant retina
Molecular and cellular neurosciences, 2015Co-Authors: Kimberly A. Fernandes, Robert W Burgess, Samuel Bloomsburg, C J Miller, Samuel A. Billingslea, Morgan M. Merrill, Richard T. Libby, Peter G FuerstAbstract:The Down syndrome cell adhesion molecule gene (DSCAM) is required for normal dendrite patterning and promotes developmental cell death in the mouse retina. Loss-of-function studies indicate that DSCAM is required for refinement of retinal ganglion cell (RGC) axons in the lateral geniculate nucleus, and in this study we report and describe a requirement for DSCAM in the maintenance of RGC axon projections within the retina. Mouse DSCAM loss of function phenotypes related to retinal ganglion cell axon outgrowth and targeting have not been previously reported, despite the abundance of axon phenotypes reported in Drosophila DSCAM1 loss and gain of function models. Analysis of the DSCAM deficient retina was performed by immunohistochemistry and Western blot analysis during postnatal development of the retina. Conditional targeting of DSCAM and Jun was performed to identify factors underlying axon-remodeling phenotypes. A subset of RGC axons were observed to project and branch extensively within the DSCAM mutant retina after eye opening. Axon remodeling was preceded by histological signs of RGC stress. These included neurofilament accumulation, axon swelling, axon blebbing and activation of JUN, JNK and AKT. Novel and extensive projection of RGC axons within the retina was observed after upregulation of these markers, and novel axon projections were maintained to at least one year of age. Further analysis of retinas in which DSCAM was conditionally targeted with Brn3b or Pax6α Cre indicated that axon stress and remodeling could occur in the absence of hydrocephalus, which frequently occurs in DSCAM mutant mice. Analysis of mice mutant for the cell death gene Bax, which executes much of DSCAM dependent cell death, identified a similar axon misprojection phenotype. Deleting Jun and DSCAM resulted in increased axon remodeling compared to DSCAM or Bax mutants. Retinal ganglion cells have a very limited capacity to regenerate after damage in the adult retina, compared to the extensive projections made in the embryo. In this study we find that DSCAM and JUN limit ectopic growth of RGC axons, thereby identifying these proteins as targets for promoting axon regeneration and reconnection.
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DSCAM promotes refinement in the mouse retina through cell death and restriction of exploring dendrites.
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2015Co-Authors: Joshua M. Sukeena, Aaron B. Simmons, Ethan J. Hansen, Renee E. Nuhn, Ivy S. Samuels, Peter G FuerstAbstract:In this study we develop and use a gain-of-function mouse allele of the Down syndrome cell adhesion molecule (DSCAM) to complement loss-of-function models. We assay the role of DSCAM in promoting cell death, spacing, and laminar targeting of neurons in the developing mouse retina. We find that ectopic or overexpression of DSCAM is sufficient to drive cell death. Gain-of-function studies indicate that DSCAM is not sufficient to increase spatial organization, prevent cell-to-cell pairing, or promote active avoidance in the mouse retina, despite the similarity of the DSCAM loss-of-function phenotype in the mouse retina to phenotypes observed in Drosophila DSCAM1 mutants. Both gain- and loss-of-function studies support a role for DSCAM in targeting neurites; DSCAM is necessary for precise dendrite lamination, and is sufficient to retarget neurites of outer retinal cells after ectopic expression. We further demonstrate that DSCAM guides dendrite targeting in type 2 dopaminergic amacrine cells, by restricting the stratum in which exploring retinal dendrites stabilize, in a DSCAM dosage-dependent manner. Based on these results we propose a single model to account for the numerous DSCAM gain- and loss-of-function phenotypes reported in the mouse retina whereby DSCAM eliminates inappropriately placed cells and connections.
Robert W Burgess - One of the best experts on this subject based on the ideXlab platform.
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DSCAM promotes self avoidance in the developing mouse retina by masking the functions of cadherin superfamily members
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Andrew M Garrett, Andre Khalil, David O Walton, Robert W BurgessAbstract:During neural development, self-avoidance ensures that a neuron’s processes arborize to evenly fill a particular spatial domain. At the individual cell level, self-avoidance is promoted by genes encoding cell-surface molecules capable of generating thousands of diverse isoforms, such as DSCAM1 (Down syndrome cell adhesion molecule 1) in Drosophila. Isoform choice differs between neighboring cells, allowing neurons to distinguish “self” from “nonself”. In the mouse retina, DSCAM promotes self-avoidance at the level of cell types, but without extreme isoform diversity. Therefore, we hypothesize that DSCAM is a general self-avoidance cue that “masks” other cell type-specific adhesion systems to prevent overly exuberant adhesion. Here, we provide in vivo and in vitro evidence that DSCAM masks the functions of members of the cadherin superfamily, supporting this hypothesis. Thus, unlike the isoform-rich molecules tasked with self-avoidance at the individual cell level, here the diversity resides on the adhesive side, positioning DSCAM as a generalized modulator of cell adhesion during neural development.
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replacing the pdz interacting c termini of DSCAM and DSCAMl1 with epitope tags causes different phenotypic severity in different cell populations
eLife, 2016Co-Authors: Andrew M Garrett, Peter G Fuerst, Abigail L D Tadenev, Yuna T Hammond, Robert W BurgessAbstract:Neurons in a part of the eye called the retina detect light and convert it into electrical signals that are sent to the brain. Different types of neurons in the retina are arranged vertically into layers and horizontally in a mosaic pattern so that two neurons of the same type are not next to each other. To establish this highly organized pattern, neurons in the developing retina must be able to recognize other neurons of the same type and avoid moving towards them – a process referred to as self-avoidance. A group of proteins called the DSCAMs are found on the surface of neurons and play key roles in positioning them in the retina. DSCAMs promote self-avoidance, help to establish connections between certain neurons and kill any excess neurons that are not needed. However, the mechanisms by which DSCAMs serve these three roles were not known. Scaffolding proteins in the cell interior interact with DSCAMs to hold them in place on the cell surface. Garrett et al. investigated whether DSCAMs need to interact with the scaffolding proteins in order to carry out any of their activities. The experiments used mice that had been genetically engineered to produce mutant DSCAM proteins that cannot bind to the scaffolding proteins. Garrett et al. hypothesized that this would affect the activities of DSCAMs in all of the different types of neurons in the retina. However, the experiments show that the mutant DSCAM proteins had different effects on the neurons. Some types of neurons developed normally, while others experienced disruptions in all three of the processes that DSCAMs are normally involved in. Some other neurons were affected to a moderate extent. This indicates that DSCAMs use different mechanisms in different types of neurons to carry out the same activities. The next step is to find out what other proteins DSCAMs need to interact with in different types of neurons.
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Novel axon projection after stress and degeneration in the DSCAM mutant retina
Molecular and cellular neurosciences, 2015Co-Authors: Kimberly A. Fernandes, Robert W Burgess, Samuel Bloomsburg, C J Miller, Samuel A. Billingslea, Morgan M. Merrill, Richard T. Libby, Peter G FuerstAbstract:The Down syndrome cell adhesion molecule gene (DSCAM) is required for normal dendrite patterning and promotes developmental cell death in the mouse retina. Loss-of-function studies indicate that DSCAM is required for refinement of retinal ganglion cell (RGC) axons in the lateral geniculate nucleus, and in this study we report and describe a requirement for DSCAM in the maintenance of RGC axon projections within the retina. Mouse DSCAM loss of function phenotypes related to retinal ganglion cell axon outgrowth and targeting have not been previously reported, despite the abundance of axon phenotypes reported in Drosophila DSCAM1 loss and gain of function models. Analysis of the DSCAM deficient retina was performed by immunohistochemistry and Western blot analysis during postnatal development of the retina. Conditional targeting of DSCAM and Jun was performed to identify factors underlying axon-remodeling phenotypes. A subset of RGC axons were observed to project and branch extensively within the DSCAM mutant retina after eye opening. Axon remodeling was preceded by histological signs of RGC stress. These included neurofilament accumulation, axon swelling, axon blebbing and activation of JUN, JNK and AKT. Novel and extensive projection of RGC axons within the retina was observed after upregulation of these markers, and novel axon projections were maintained to at least one year of age. Further analysis of retinas in which DSCAM was conditionally targeted with Brn3b or Pax6α Cre indicated that axon stress and remodeling could occur in the absence of hydrocephalus, which frequently occurs in DSCAM mutant mice. Analysis of mice mutant for the cell death gene Bax, which executes much of DSCAM dependent cell death, identified a similar axon misprojection phenotype. Deleting Jun and DSCAM resulted in increased axon remodeling compared to DSCAM or Bax mutants. Retinal ganglion cells have a very limited capacity to regenerate after damage in the adult retina, compared to the extensive projections made in the embryo. In this study we find that DSCAM and JUN limit ectopic growth of RGC axons, thereby identifying these proteins as targets for promoting axon regeneration and reconnection.
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A Novel Mouse DSCAM Mutation Inhibits Localization and Shedding of DSCAM
PloS one, 2012Co-Authors: R. Dee Schramm, Robert W Burgess, Belinda S Harris, Ryan P. Rounds, F. Marty Ytreberg, Peter G FuerstAbstract:The differential adhesion hypothesis of development states that patterning of organisms, organs and tissues is mediated in large part by expression of cell adhesion molecules. The cues provided by cell adhesion molecules are also hypothesized to facilitate specific connectivity within the nervous system. In this study we characterize a novel mouse mutation in the gene DSCAM (Down Syndrome Cell Adhesion Molecule). Vertebrate DSCAM is required for normal development of the central nervous system and has been best characterized in the visual system. In the visual system DSCAM is required for regulation of cell number, mosaic formation, laminar specificity, and refinement of retinal-tectal projections. We have identified a novel mutation in DSCAM that results in a single amino acid substitution, R1018P, in the extracellular domain of the DSCAM protein. Mice homozygous for the R1018P mutation develop a subset of defects observed in DSCAM null mice. In vitro analysis identified defects in DSCAMR1018P localization to filopodia. We also find that wild type DSCAM protein is constitutively cleaved and shed from transfected cells. This secretion is inhibited by the R1018P mutation. We also characterized a novel splice isoform of DSCAM and identified defects in lamination of type 2 and type 6 cone bipolar cells in DSCAM mutant mice. The identification and characterization of partial loss of function mutations in genes such as DSCAM will be helpful in predicting signs and symptoms that may be observed in human patients with partial loss of DSCAM function.
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neuronal clustering and fasciculation phenotype in DSCAM and bax deficient mouse retinas
The Journal of Comparative Neurology, 2012Co-Authors: Patrick W Keeley, Peter G Fuerst, Robert W Burgess, Buranee J Sliff, Sammy C S Lee, Stephen J Eglen, Benjamin E ReeseAbstract:Individual types of retinal neurons are distributed to minimize proximity to neighboring cells. Many of these same cell types extend dendrites to provide coverage of the retinal surface. These two cardinal features of retinal mosaics are disrupted, for certain cell types, in mice deficient for the Down syndrome cell adhesion molecule, DSCAM, exhibiting an aberrant clustering of somata and fasciculation of dendrites. The DSCAM mutant mouse retina also exhibits excess numbers of these same cell types. The present study compared these two features in DSCAM mutant retinas with the Bax knockout retina, in which excess numbers of two of these cell types, the melanopsin-positive retinal ganglion cells (MRGCs) and the dopaminergic amacrine cells (DACs), are also present. Whole retinas were immunolabeled for both populations, and every labeled soma was plotted. For the MRGCs, we found a gene dosage effect for DSCAM, with the DSCAM+/- retinas showing smaller increases in cell number, clustering, and fasciculation. Curiously, Bax-/- retinas, showing numbers of MRGCs intermediate to those found in the DSCAM-/- and DSCAM+/- retinas, also had clustering and fasciculation phenotypes that were intermediate to retinas with those genotypes. DACs, by comparison, showed changes in both the DSCAM-/- and the Bax-/- retinas that did not correlate with their increases in DAC number. The fasciculation phenotype in the DSCAM-/- retina was particularly prominent despite only modest clustering. These results demonstrate that the somal clustering and fasciculation observed in the DSCAM mutant retina are not unique to DSCAM deficiency and are manifested distinctively by different retinal cell types.
Tzumin Lee - One of the best experts on this subject based on the ideXlab platform.
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Molecular diversity of DSCAM and self-recognition.
Advances in experimental medicine and biology, 2012Co-Authors: Lei Shi, Tzumin LeeAbstract:Cell recognition requires interactions through molecules located on cell surface. The insect homolog of Down syndrome cell adhesion molecule (DSCAM) manifests huge molecular diversity in its extracellular domain. High-affinity DSCAM-DSCAM interactions only occur between isoforms that carry identical extracellular domains. Homophilic DSCAM signaling can, thus, vary in strength depending on the compositions of DSCAMs present on the opposing cell surfaces. DSCAM abundantly exists in the developing nervous system and governs arborization and proper elaboration of neurites. Notably, individual neurons may stochastically and dynamically express a small subset of DSCAM isoforms such that any given neurite can be endowed with a unique repertoire of DSCAMs. This allows individual neurites to recognize their sister branches. Self-recognition leads to self-repulsion, ensuring divergent migration of sister processes. By contrast, weak homophilic DSCAM interactions may promote fasciculation of neurites that express analogous, but not identical, DSCAMs. Differential DSCAM binding may provide graded cell recognition that in turn governs complex neuronal morphogenesis.
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Dynein-Dynactin Complex Is Essential for Dendritic Restriction of TM1-Containing Drosophila DSCAM
PloS one, 2008Co-Authors: Jacob S. Yang, Jia-min Bai, Tzumin LeeAbstract:Background Many membrane proteins, including Drosophila DSCAM, are enriched in dendrites or axons within neurons. However, little is known about how the differential distribution is established and maintained. Methodology/Principal Findings Here we investigated the mechanisms underlying the dendritic targeting of DSCAM[TM1]. Through forward genetic mosaic screens and by silencing specific genes via targeted RNAi, we found that several genes, encoding various components of the dynein-dynactin complex, are required for restricting DSCAM[TM1] to the mushroom body dendrites. In contrast, compromising dynein/dynactin function did not affect dendritic targeting of two other dendritic markers, Nod and Rdl. Tracing newly synthesized DSCAM[TM1] further revealed that compromising dynein/dynactin function did not affect the initial dendritic targeting of DSCAM[TM1], but disrupted the maintenance of its restriction to dendrites. Conclusions/Significance The results of this study suggest multiple mechanisms of dendritic protein targeting. Notably, dynein-dynactin plays a role in excluding dendritic DSCAM, but not Rdl, from axons by retrograde transport.
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Specific Drosophila DSCAM Juxtamembrane Variants Control Dendritic Elaboration and Axonal Arborization
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2007Co-Authors: Lei Shi, Jacob S. Yang, Tzumin LeeAbstract:Drosophila DSCAM isoforms are derived from two alternative transmembrane/juxtamembrane domains (TMs) in addition to thousands of ectodomain variants. Using a microRNA-based RNA interference technology, we selectively knocked down different subsets of DSCAMs containing either the exon 17.1- or exon 17.2-encoding TM. Eliminating DSCAM[TM1] reduced DSCAM expression but minimally affected postembryonic axonal morphogenesis. In contrast, depleting DSCAM[TM2] blocked axon arborization. Further removal of DSCAM[TM1] enhanced the loss-of-DSCAM[TM2] axonal phenotypes. However, DSCAM[TM1] primarily regulates dendritic development, as evidenced by the observations that removing DSCAM[TM1] alone impeded elaboration of dendrites and that transgenic DSCAM[TM1], but not DSCAM[TM2], effectively rescued DSCAM mutant dendritic phenotypes in mosaic organisms. These distinct DSCAM functions can be attributed to the juxtamembrane regions of TMs that govern dendritic versus axonal targeting of DSCAM as well. Together, we suggest that specific Drosophila DSCAM juxtamembrane variants control dendritic elaboration and axonal arborization.
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Transmembrane/juxtamembrane domain-dependent DSCAM distribution and function during mushroom body neuronal morphogenesis.
Neuron, 2004Co-Authors: Jian Wang, Jacob S. Yang, Xiaoyan Zheng, Christopher T Zugates, Ching-hsien J. Lee, Tzumin LeeAbstract:Besides 19,008 possible ectodomains, Drosophila DSCAM contains two alternative transmembrane/juxtamembrane segments, respectively, derived from exon 17.1 and exon 17.2. We wondered whether specific DSCAM isoforms mediate formation and segregation of axonal branches in the Drosophila mushroom bodies (MBs). Removal of various subsets of the 12 exon 4s does not affect MB neuronal morphogenesis, while expression of a DSCAM transgene only partially rescues DSCAM mutant phenotypes. Interestingly, differential rescuing effects are observed between two DSCAM transgenes that each possesses one of the two possible exon 17s. Axon bifurcation/segregation abnormalities are better rescued by the exon 17.2-containing transgene, but coexpression of both transgenes is required for rescuing mutant viability. Meanwhile, exon 17.1 targets ectopically expressed DSCAM-GFP to dendrites while DSCAM[exon 17.2]-GFP is enriched in axons; only DSCAM[exon 17.2] affects MB axons. These results suggest that exon 17.1 is minimally involved in axonal morphogenesis and that morphogenesis of MB axons probably involves multiple distinct exon 17.2-containing DSCAM isoforms.
Jian Wang - One of the best experts on this subject based on the ideXlab platform.
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Human down syndrome cell adhesion molecules (DSCAMs) are functionally conserved with Drosophila DSCAM[TM1] isoforms in controlling neurodevelopment
Insect biochemistry and molecular biology, 2011Co-Authors: Jianhua Huang, Ying Wang, Sangeetha Raghavan, Siqian Feng, Kurtis Kiesewetter, Jian WangAbstract:Drosophila Down syndrome cell adhesion molecule (DSCAM) potentially produces more than 150,000 cell adhesion molecules that share two alternative transmembrane/juxtamembrane (TM) domains, which dictate the dendrite versus axon subcellular distribution and function of different DSCAM isoforms. Vertebrate genomes contain two closely related genes, DSCAM and DSCAM-Like1 (DSCAML1), which do not have extensive alternative splicing. We investigated the functional conservation between invertebrate DSCAMs and vertebrate DSCAMs by cross-species rescue assays and found that human DSCAM and DSCAML1 partially, but substantially, rescued the larval lethality of Drosophila DSCAM mutants. Interestingly, both human DSCAM and DSCAML1 were targeted to the dendrites in Drosophila neurons, had synergistic rescue effects with Drosophila DSCAM[TM2], and preferentially rescued the dendrite defects of Drosophila DSCAM mutant neurons. Therefore, human DSCAM and DSCAML1 are functionally conserved with Drosophila DSCAM[TM1] isoforms.
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Endodomain Diversity in the Drosophila DSCAM and Its Roles in Neuronal Morphogenesis
The Journal of Neuroscience, 2009Co-Authors: Hung-hsiang Yu, Jacob S. Yang, Jian Wang, Yaling HuangAbstract:Drosophila Down syndrome cell adhesion molecule (DSCAM) can be variably spliced to encode 152,064 distinct single-pass transmembrane proteins. In addition to 19,008 possible ectodomains and two alternative transmembrane segments, it may carry endodomains containing or lacking exons 19 and 23. Here, we determine the role of DSCAM endodomain diversity in neural development. DSCAM with full-length endodomain is largely restricted to embryogenesis. In contrast, most DSCAMs lack exons 19 and 23 at postembryonic stages. As implicated from the expression patterns, removal of DSCAM exon 19-containing variants disrupts wiring of embryonic neurons while silencing of DSCAM transcripts lacking exon 19 or exon 23 effectively blocks postembryonic neuronal morphogenesis. Furthermore, compared with exon 19-containing DSCAM, transgenic DSCAM without exon 19 is more efficiently targeted to neurites and more potently suppresses axon bifurcation in DSCAM mutant neurons. In sum, DSCAM with or without exon 19 in its endodomain is used to govern different stage-specific neuronal morphogenetic processes, possibly due to differences in protein targeting.
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transmembrane juxtamembrane domain dependent DSCAM distribution and function during mushroom body neuronal morphogenesis
Neuron, 2004Co-Authors: Jian Wang, Jacob S. Yang, Xiaoyan Zheng, Christopher T ZugatesAbstract:Besides 19,008 possible ectodomains, Drosophila DSCAM contains two alternative transmembrane/juxtamembrane segments, respectively, derived from exon 17.1 and exon 17.2. We wondered whether specific DSCAM isoforms mediate formation and segregation of axonal branches in the Drosophila mushroom bodies (MBs). Removal of various subsets of the 12 exon 4s does not affect MB neuronal morphogenesis, while expression of a DSCAM transgene only partially rescues DSCAM mutant phenotypes. Interestingly, differential rescuing effects are observed between two DSCAM transgenes that each possesses one of the two possible exon 17s. Axon bifurcation/segregation abnormalities are better rescued by the exon 17.2-containing transgene, but coexpression of both transgenes is required for rescuing mutant viability. Meanwhile, exon 17.1 targets ectopically expressed DSCAM-GFP to dendrites while DSCAM[exon 17.2]-GFP is enriched in axons; only DSCAM[exon 17.2] affects MB axons. These results suggest that exon 17.1 is minimally involved in axonal morphogenesis and that morphogenesis of MB axons probably involves multiple distinct exon 17.2-containing DSCAM isoforms.
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Transmembrane/juxtamembrane domain-dependent DSCAM distribution and function during mushroom body neuronal morphogenesis.
Neuron, 2004Co-Authors: Jian Wang, Jacob S. Yang, Xiaoyan Zheng, Christopher T Zugates, Ching-hsien J. Lee, Tzumin LeeAbstract:Besides 19,008 possible ectodomains, Drosophila DSCAM contains two alternative transmembrane/juxtamembrane segments, respectively, derived from exon 17.1 and exon 17.2. We wondered whether specific DSCAM isoforms mediate formation and segregation of axonal branches in the Drosophila mushroom bodies (MBs). Removal of various subsets of the 12 exon 4s does not affect MB neuronal morphogenesis, while expression of a DSCAM transgene only partially rescues DSCAM mutant phenotypes. Interestingly, differential rescuing effects are observed between two DSCAM transgenes that each possesses one of the two possible exon 17s. Axon bifurcation/segregation abnormalities are better rescued by the exon 17.2-containing transgene, but coexpression of both transgenes is required for rescuing mutant viability. Meanwhile, exon 17.1 targets ectopically expressed DSCAM-GFP to dendrites while DSCAM[exon 17.2]-GFP is enriched in axons; only DSCAM[exon 17.2] affects MB axons. These results suggest that exon 17.1 is minimally involved in axonal morphogenesis and that morphogenesis of MB axons probably involves multiple distinct exon 17.2-containing DSCAM isoforms.
S. Lawrence Zipursky - One of the best experts on this subject based on the ideXlab platform.
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A Double S Shape Provides the Structural Basis for the Extraordinary Binding Specificity of DSCAM Isoforms
Cell, 2008Co-Authors: Michael R. Sawaya, Woj M. Wojtowicz, Ingemar André, Bin Qian, David Baker, David Eisenberg, S. Lawrence ZipurskyAbstract:Summary Drosophila DSCAM encodes a vast family of immunoglobulin (Ig)-containing proteins that exhibit isoform-specific homophilic binding. This diversity is essential for cell recognition events required for wiring the brain. Each isoform binds to itself but rarely to other isoforms. Specificity is determined by "matching" of three variable Ig domains within an ∼220 kD ectodomain. Here, we present the structure of the homophilic binding region of DSCAM, comprising the eight N-terminal Ig domains (DSCAM 1–8 ). DSCAM 1–8 forms a symmetric homodimer of S-shaped molecules. This conformation, comprising two reverse turns, allows each pair of the three variable domains to "match" in an antiparallel fashion. Structural, genetic, and biochemical studies demonstrate that, in addition to variable domain "matching," intramolecular interactions between constant domains promote homophilic binding. These studies provide insight into how "matching" at all three pairs of variable domains in DSCAM mediates isoform-specific recognition.
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DSCAM-mediated repulsion controls tiling and self-avoidance.
Current opinion in neurobiology, 2008Co-Authors: S. Sean Millard, S. Lawrence ZipurskyAbstract:Recent studies have uncovered the molecular basis of self-avoidance and tiling, two fundamental principles required for the formation of neural circuits. Both of these wiring strategies are established through homophilic repulsion between DSCAM proteins expressed on opposing cell surfaces. In Drosophila, DSCAM1 mediates self-avoidance, whereas DSCAM2 mediates tiling. By contrast, phenotypes in the retina of the DSCAM mutant mouse indicate that DSCAM functions in both self-avoidance and tiling. These findings suggest that homophilic recognition molecules that have classically been defined as adhesive may also function as repulsive cues and that DSCAM proteins specialize in this function.
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DSCAM-Mediated Cell Recognition Regulates Neural Circuit Formation
Annual review of cell and developmental biology, 2008Co-Authors: Daisuke Hattori, S. Sean Millard, Woj M. Wojtowicz, S. Lawrence ZipurskyAbstract:The DSCAM family of immunoglobulin cell surface proteins mediates recognition events between neurons that play an essential role in the establishment of neural circuits. The Drosophila DSCAM1 locus encodes tens of thousands of cell surface proteins via alternative splicing. These isoforms exhibit exquisite isoform-specific binding in vitro that mediates homophilic repulsion in vivo. These properties provide the molecular basis for self-avoidance, an essential developmental mechanism that al- lows axonal and dendritic processes to uniformly cover their synaptic fields. In a mechanistically similar fashion, homophilic repulsion me- diated by Drosophila DSCAM2 prevents processes from the same class of cells from occupying overlapping synaptic fields through a process called tiling. Genetic studies in the mouse visual system support the view that vertebrate DSCAM also promotes both self-avoidance and tiling. By contrast, DSCAM and DSCAM-L promote layer-specific targeting in the chick visual system, presumably through promoting homophilic adhesion. The fly and mouse studies underscore the importance of ho- mophilic repulsion in regulating neural circuit assembly, whereas the chick studies suggest that DSCAM proteins may mediate a variety of dif- ferent recognition events during wiring in a context-dependent fashion.
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DSCAM diversity is essential for neuronal wiring and self-recognition.
Nature, 2007Co-Authors: Daisuke Hattori, S. Lawrence Zipursky, Ebru Demir, Ho Won Kim, Erika Viragh, Barry J. DicksonAbstract:The complexity and specificity of neuronal wiring implies the existence of a cellular recognition code that allows neurons to distinguish between one another. The remarkable diversity of the immunoglobulin superfamily protein DSCAM (for Down syndrome cell adhesion molecule) may be part of that system. DSCAM plays a crucial role in making Drosophila neurons able to distinguish between self and non-self, and is essential to patterning neural circuits. Use of a novel approach to generate mosaic animals shows that Down syndrome cell adhesion molecules (DSCAM) diversity plays a crucial role in providing neurons in the Drosophila central nervous system with the ability to distinguish between self and non-self, which is essential to patterning neural circuits. Neurons are thought to use diverse families of cell-surface molecules for cell recognition during circuit assembly. In Drosophila, alternative splicing of the Down syndrome cell adhesion molecule (DSCAM) gene potentially generates 38,016 closely related transmembrane proteins of the immunoglobulin superfamily, each comprising one of 19,008 alternative ectodomains linked to one of two alternative transmembrane segments1. These ectodomains show isoform-specific homophilic binding, leading to speculation that DSCAM proteins mediate cell recognition2. Genetic studies have established that DSCAM is required for neural circuit assembly1,3,4,5,6,7,8,9,10, but the extent to which isoform diversity contributes to this process is not known. Here we provide conclusive evidence that DSCAM diversity is essential for circuit assembly. Using homologous recombination, we reduced the entire repertoire of DSCAM ectodomains to just a single isoform. Neural circuits in these mutants are severely disorganized. Furthermore, we show that it is crucial for neighbouring neurons to express distinct isoforms, but that the specific identity of the isoforms expressed in an individual neuron is unimportant. We conclude that DSCAM diversity provides each neuron with a unique identity by which it can distinguish its own processes from those of other neurons, and that this self-recognition is essential for wiring the Drosophila brain.
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Analysis of DSCAM Diversity in Regulating Axon Guidance in Drosophila Mushroom Bodies
Neuron, 2004Co-Authors: Xiao-li Zhan, Daisuke Hattori, James C Clemens, Thomas Hummel, Guilherme Neves, John J. Flanagan, M.luisa Vasconcelos, Andrew Chess, S. Lawrence ZipurskyAbstract:DSCAM is an immunoglobulin (Ig) superfamily member that regulates axon guidance and targeting in Drosophila. Alternative splicing potentially generates 38,016 isoforms differing in their extracellular Ig and transmembrane domains. We demonstrate that DSCAM mediates the sorting of axons in the developing mushroom body (MB). This correlates with the precise spatiotemporal pattern of DSCAM protein expression. We demonstrate that MB neurons express different arrays of DSCAM isoforms and that single MB neurons express multiple isoforms. Two different DSCAM isoforms differing in their extracellular domains introduced as transgenes into single mutant cells partially rescued the mutant phenotype. Expression of one isoform of DSCAM in a cohort of MB neurons induced dominant phenotypes, while expression of a single isoform in a single cell did not. We propose that different extracellular domains of DSCAM share a common function and that differences in isoforms expressed on the surface of neighboring axons influence interactions between them.
