- Phosphatidylinositol-3-phosphate regulates sorting and processing of amyloid precursor protein through the endosomal system
Morel E, Chamoun Z, Lasiecka ZM, Chan RB, Williamson RL, Vetanovetz C, Dall’Armi C, Simoes S, Point Du Jour KS, McCabe BD, Small SA, Di Paolo G.
Nature Communications 4:2250 doi:10.1038/ncomms3250[+]Defects in endosomal sorting have been implicated in Alzheimer’s disease. Endosomal traffic is largely controlled by phosphatidylinositol-3-phosphate, a phosphoinositide synthesized primarily by lipid kinase Vps34. Here we show that phosphatidylinositol-3-phosphate is selectively deficient in brain tissue from humans with Alzheimer’s disease and Alzheimer’s disease mouse models. Silencing Vps34 causes an enlargement of neuronal endosomes, enhances the amyloidogenic processing of amyloid precursor protein in these organelles and reduces amyloid precursor protein sorting to intraluminal vesicles. This trafficking phenotype is recapitulated by silencing components of the endosomal sorting complex required for transport (ESCRT) pathway, including the phosphatidylinositol-3-phosphate effector Hrs and Tsg101. Amyloid precursor protein is ubiquitinated, and interfering with this process by targeted mutagenesis alters sorting of amyloid precursor protein to the intraluminal vesicles of endosomes and enhances amyloid-beta peptide generation. In addition to establishing phosphatidylinositol-3-phosphate deficiency as a contributing factor in Alzheimer’s disease, these results clarify the mechanisms of amyloid precursor protein trafficking through the endosomal system in normal and pathological states.
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- Amphetamine-induced behavior requires CaMKII-dependent dopamine transporter phosphorylation
Pizzo AB, Karam CS, Zhang Y, Ma CL, McCabe BD, Javitch JA.
Molecular Psychiatry doi:10.1038/mp.2013.29[+]The dopamine (DA) transporter (DAT), which mediates the inactivation of released DA through its reuptake, is a primary molecular target for psychostimulants. Cocaine and methylphenidate (MPH) exert their psychostimulant properties by blocking DA reuptake, leading to the elevation of extracellular DA. In contrast, amphetamine (AMPH) acts as a substrate for DAT and subsequently induces non-exocytotic DAT-mediated release of DA (DA efflux). Here we use a Drosophila behavioral assay to delineate the signaling mechanisms that modulate DAT-mediated AMPH-induced behavior in vivo. Understanding these mechanisms is critical to understanding how the actions of AMPH might be blocked therapeutically, while simultaneously preserving DA transport.
- RAB7L1 Interacts with LRRK2 to Modify Intraneuronal Protein Sorting and Parkinson’s Disease Risk
Macleod DA, Rhinn H, Kuwahara T, Zolin A, Di Paolo G, McCabe BD, Marder KS, Honig LS, Clark LN, Small SA, Abeliovich A.
Neuron 77: 425–439[+]Recent genome-wide association studies have linked common variants in the human genome to Parkinson’s disease (PD) risk. Here we show that the consequences of variants at 2 such loci, PARK16 and LRRK2, are highly interrelated, both in terms of their broad impacts on human brain transcriptomes of unaffected carriers, and in terms of their associations with PD risk. Deficiency of the PARK16 locus gene RAB7L1 in primary rodent neurons, or of a RAB7L1 ortholog in Drosophila dopamine neurons, recapitulated degeneration observed with expression of a familial PD mutant form of LRRK2, whereas RAB7L1 overexpression rescued the LRRK2 mutant phenotypes. PD-associated defects in RAB7L1 or LRRK2 led to endolysosomal and Golgi apparatus sorting defects and deficiency of the VPS35 component of the retromer complex. Expression of wild-type VPS35, but not a familial PD-associated mutant form, rescued these defects. Taken together, these studies implicate retromer and lysosomal pathway alterations in PD risk.
Pubmed Journal Review
- SMN is required for Sensory-Motor Circuit Function in Drosophila
Imlach WL, Beck ES, Choi BJ, Lotti F, Pellizzoni L, McCabe BD.
Cell 151: 427–439[+]Spinal muscular atrophy (SMA) is a lethal human disease characterized by motor neuron dysfunction and muscle deterioration due to depletion of the ubiquitous survival motor neuron (SMN) protein. Drosophila SMN mutants have reduced muscle size and defective locomotion, motor rhythm, and motor neuron neurotransmission. Unexpectedly, restoration of SMN in either muscles or motor neurons did not alter these phenotypes. Instead, SMN must be expressed in proprioceptive neurons and interneurons in the motor circuit to nonautonomously correct defects in motor neurons and muscles. SMN depletion disrupts the motor system subsequent to circuit development and can be mimicked by the inhibition of motor network function. Furthermore, increasing motor circuit excitability by genetic or pharmacological inhibition of K+ channels can correct SMN- dependent phenotypes. These results establish sensory-motor circuit dysfunction as the origin of motor system deficits in this SMA model and suggest that enhancement of motor neural network activity could ameliorate the disease.
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- An SMN-Dependent U12 Splicing Event Essential for Motor Circuit Function
Lotti F, Imlach WL, Saieva L, Beck ES, Hao LT, Li DK, Jiao W, Mentis GZ, Beattie CE, McCabe BD*, Pellizzoni L*
Cell 151: 440–454[+]Spinal muscular atrophy (SMA) is a motor neuron disease caused by deficiency of the ubiquitous survival motor neuron (SMN) protein. To define the mechanisms of selective neuronal dysfunction in SMA, we investigated the role of SMN-dependent U12 splicing events in the regulation of motor circuit activity. We show that SMN deficiency perturbs splicing and decreases the expression of a subset of U12 intron-containing genes in mammalian cells and Drosophila larvae. Analysis of these SMN target genes identifies Stasimon as a protein required for motor circuit function. Restoration of Stasimon expression in the motor circuit corrects defects in neuromuscular junction transmission and muscle growth in Drosophila SMN mutants and aberrant motor neuron development in SMN-deficient zebra- fish. These findings directly link defective splicing of critical neuronal genes induced by SMN deficiency to motor circuit dysfunction, establishing a molecular framework for the selective pathology of SMA. * corresponding
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- A modular toolset for recombination transgenesis and neurogenetic analysis of Drosophila.
Wang JW, Beck ES, McCabe BD.
PLoS One 7:e42102[+]Transgenic Drosophila have contributed extensively to our understanding of nervous system development, physiology and behavior in addition to being valuable models of human neurological disease. Here, we have generated a novel series of modular transgenic vectors designed to optimize and accelerate the production and analysis of transgenes in Drosophila. We constructed a novel vector backbone, pBID, that allows both phiC31 targeted transgene integration and incorporates insulator sequences to ensure specific and uniform transgene expression. Upon this framework, we have built a series of constructs that are either backwards compatible with existing restriction enzyme based vectors or utilize Gateway recombination technology for high-throughput cloning. These vectors allow for endogenous promoter or Gal4 targeted expression of transgenic proteins with or without fluorescent protein or epitope tags. In addition, we have generated constructs that facilitate transgenic splice isoform specific RNA inhibition of gene expression. We demonstrate the utility of these constructs to analyze proteins involved in nervous system development, physiology and neurodegenerative disease. We expect that these reagents will facilitate the proficiency and sophistication of Drosophila genetic analysis in both the nervous system and other tissues.
- The membrane raft protein Flotillin-1 is essential in dopamine neurons for amphetamine-induced behavior in Drosophila.
Pizzo AB, Karam CS, Zhang Y, Yano H, Freyberg RJ, Karam DS, Freyberg Z, Yamamoto A, McCabe BD, Javitch JA.
Molecular Psychiatry doi:10.1038/mp.2012.82[+]The dopamine transporter (DAT) is the primary molecular target responsible for the rewarding properties of the psychostimulants amphetamine (AMPH) and cocaine. AMPH increases extracellular dopamine (DA) by promoting its nonexocytotic release via DAT-mediated efflux. Previous studies in heterologous cells have shown that phosphorylation of the amino terminus of DAT is required for AMPH-induced DA efflux but not for DA uptake. However, the identity of many of the modulatory proteins and the molecular mechanisms that coordinate efflux and the ensuing behavioral effects remain poorly defined. Here, we establish a robust assay for AMPH-induced hyperlocomotion in Drosophila melanogaster larvae. Using a variety of genetic and pharmacological approaches, we demonstrate that this behavioral response is dependent on DA and on DAT and its phosphorylation. We also show that methylphenidate (MPH), which competitively inhibits DA uptake but does not induce DAT-mediated DA efflux, also leads to DAT-dependent hyperlocomotion, but this response is independent of DAT phosphorylation. Moreover, we demonstrate that the membrane raft protein Flotillin-1 is required for AMPH-induced, but not MPH-induced, hyperlocomotion. These results are the first evidence of a role for a raft protein in an AMPH-mediated behavior. Thus, using our assay we are able to translate molecular and cellular findings to a behavioral level and to differentiate in vivo the distinct mechanisms of two psychostimulants
- Regulation of Fasciclin II and Synaptic Terminal Development by the Splicing Factor Beag.
Beck ES, Gasque G, Imlach WL, Jiao W, Choi BJ, Wu PS, Kraushar ML, McCabe BD.
Journal of Neuroscience 20:7058-73[+]Pre-mRNA alternative splicing is an important mechanism for the generation of synaptic protein diversity, but few factors governing this process have been identified. From a screen for Drosophila mutants with aberrant synaptic development, we identified beag, a mutant with fewer synaptic boutons and decreased neurotransmitter release. Beag encodes a spliceosomal protein similar to splicing factors in humans and Caenorhabditis elegans. We find that both beag mutants and mutants of an interacting gene dsmu1 have changes in the synaptic levels of specific splice isoforms of Fasciclin II (FasII), the Drosophila ortholog of neural cell adhesion molecule. We show that restoration of one splice isoform of FasII can rescue synaptic morphology in beag mutants while expression of other isoforms cannot. We further demonstrate that this FasII isoform has unique functions in synaptic development independent of transsynaptic adhesion. beag and dsmu1 mutants demonstrate an essential role for these previously uncharacterized splicing factors in the regulation of synapse development and function.
- The p150(Glued) CAP-Gly Domain Regulates Initiation of Retrograde Transport at Synaptic Termini.
Lloyd TE, Machamer J, O'Hara K, Kim JH, Collins SE, Wong MY, Sahin B, Imlach W, Yang Y, Levitan ES, McCabe BD, Kolodkin AL.
Neuron 74:344-60.[+]p150(Glued) is the major subunit of dynactin, a complex that functions with dynein in minus-end-directed microtubule transport. Mutations within the p150(Glued) CAP-Gly microtubule-binding domain cause neurodegenerative diseases through an unclear mechanism. A p150(Glued) motor neuron degenerative disease-associated mutation introduced into the Drosophila Glued locus generates a partial loss-of-function allele (Gl(G38S)) with impaired neurotransmitter release and adult-onset locomotor dysfunction. Disruption of the p150(Glued) CAP-Gly domain in neurons causes a specific disruption of vesicle trafficking at terminal boutons (TBs), the distal-most ends of synapses. Gl(G38S) larvae accumulate endosomes along with dynein and kinesin motor proteins within swollen TBs, and genetic analyses show that kinesin and p150(Glued) function cooperatively at TBs to coordinate transport. Therefore, the p150(Glued) CAP-Gly domain regulates dynein-mediated retrograde transport at synaptic termini, and this function of dynactin is disrupted by a mutation that causes motor neuron disease.
Pubmed Journal Review
- The ALS-associated proteins FUS and TDP-43 function together to affect Drosophila locomotion and life span.
Wang JW, Brent JR, Tomlinson A, Shneider NA, McCabe BD.
Journal of Clinical Investigation 21:4118-26[+]The fatal adult motor neuron disease amyotrophic lateral sclerosis (ALS) shares some clinical and pathological overlap with frontotemporal dementia (FTD), an early-onset neurodegenerative disorder. The RNA/DNA-binding proteins fused in sarcoma (FUS; also known as TLS) and TAR DNA binding protein-43 (TDP-43) have recently been shown to be genetically and pathologically associated with familial forms of ALS and FTD. It is currently unknown whether perturbation of these proteins results in disease through mechanisms that are independent of normal protein function or via the pathophysiological disruption of molecular processes in which they are both critical. Here, we report that Drosophila mutants in which the homolog of FUS is disrupted exhibit decreased adult viability, diminished locomotor speed, and reduced life span compared with controls. These phenotypes were fully rescued by wild-type human FUS, but not ALS-associated mutant FUS proteins. A mutant of the Drosophila homolog of TDP-43 had similar, but more severe, deficits. Through cross-rescue analysis, we demonstrated that FUS acted together with and downstream of TDP-43 in a common genetic pathway in neurons. Furthermore, we found that these proteins associated with each other in an RNA-dependent complex. Our results establish that FUS and TDP-43 function together in vivo and suggest that molecular pathways requiring the combined activities of both of these proteins may be disrupted in ALS and FTD.
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- Drosophila larval NMJ immunohistochemistry.
Brent J, Werner K, McCabe BD.
Journal of Visualized Experiments 28: doi: 10.3791/1108.[+]The Drosophila neuromuscular junction (NMJ) is an established model system used for the study of synaptic development and plasticity. The widespread use of the Drosophila motor system is due to its high accessibility. It can be analyzed with single-cell resolution. There are 30 muscles per hemisegment whose arrangement within the peripheral body wall are known. A total of 31 motor neurons attach to these muscles in a pattern that has high fidelity. Using molecular biology and genetics, one can create transgenic animals or mutants. Then, one can study the developmental consequences on the morphology and function of the NMJ. Immunohistochemistry can be used to clearly image the components of the NMJ. In this article, we demonstrate how to use antibody staining to visualize the Drosophila larval NMJ.
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- Drosophila larval NMJ dissection.
Brent JR, Werner KM, McCabe BD.
Journal of Visualized Experiments 24: doi: 10.3791/1107.[+]The Drosophila neuromuscular junction (NMJ) is an established model system used for the study of synaptic development and plasticity. The widespread use of the Drosophila motor system is due to its high accessibility. It can be analyzed with single-cell resolution. There are 30 muscles per hemisegment whose arrangement within the peripheral body wall are known. A total of 35 motor neurons attach to these muscles in a pattern that has high fidelity. Using molecular biology and genetics, one can create transgenic animals or mutants. Then, one can study the developmental consequences on the morphology and function of the NMJ. In order to access the NMJ for study, it is necessary to carefully dissect each larva. In this article we demonstrate how to properly dissect Drosophila larvae for study of the NMJ by removing all internal organs while leaving the body wall intact. This technique is suitable to prepare larvae for imaging, immunohistochemistry, or electrophysiology.
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- Electrophysiological methods for recording synaptic potentials from the NMJ of Drosophila larvae.
Imlach W, McCabe BD.
Journal of Visualized Experiments 24: doi: 10.3791/1109.[+]In this video, we describe the electrophysiological methods for recording synaptic transmission at the neuromuscular junction (NMJ) of Drosophila larva. The larval neuromuscular system is a model synapse for the study of synaptic physiology and neurotransmission, and is a valuable research tool that has defined genetics and is accessible to experimental manipulation. Larvae can be dissected to expose the body wall musculature, central nervous system, and peripheral nerves. The muscles of Drosophila and their innervation pattern are well characterized and muscles are easy to access for intracellular recording. Individual muscles can be identified by their location and orientation within the 8 abdominal segments, each with 30 muscles arranged in a pattern that is repeated in segments A2 - A7. Dissected drosophila larvae are thin and individual muscles and bundles of motor neuron axons can be visualized by transillumination(1). Transgenic constructs can be used to label target cells for visual identification or for manipulating gene products in specific tissues. In larvae, excitatory junction potentials (EJP's) are generated in response to vesicular release of glutamate from the motoneurons at the synapse. In dissected larvae, the EJP can be recorded in the muscle with an intracellular electrode. Action potentials can be artificially evoked in motor neurons that have been cut posterior to the ventral ganglion, drawn into a glass pipette by gentle suction and stimulated with an electrode. These motor neurons have distinct firing thresholds when stimulated, and when they fire simultaneously, they generate a response in the muscle. Signals transmitted across the NMJ synapse can be recorded in the muscles that the motor neurons innervate. The EJP's and minature excitatory junction potentials (mEJP's) are seen as changes in membrane potential. Electrophysiological responses are recorded at room temperature in modified minimal hemolymph-like solution(2) (HL3) that contains 5 mM Mg(2+) and 1.5 mM Ca(2+). Changes in the amplitude of evoked EJP's can indicate differences in synaptic function and structure. Digitized recordings are analyzed for EJP amplitude, mEJP frequency and amplitude, and quantal content.
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- Parkinson’s disease: Insights from Invertebrates.
Penney, E.B. and McCabe B.D.
in Parkinson's Disease: Pathogenic and Therapeutic Insights from Toxin and Genetic Models, Academic Press, edited by Richard Nass and Serge Przedborski[+]Parkinson’s disease (PD) is the most common neurodegenerative movement disorder, effecting 1% of the population over the age of 60. Over the past two decades, significant progress has been made in our understanding of the genetic and environmental factors that predispose some people to develop PD, however the exact molecular and cellular mechanisms that underlie the disease remain unclear and current treatments remain primarily palliative. An arsenal of scientific approaches are being applied to study PD and the following chapters detail a relatively recent addition to the armory of human disease biology – modeling disease in invertebrate genetic organisms. In this overview, we will outline the rationale for these studies and highlight both the promise and the pitfalls that invertebrate model systems offer to both elucidate PD pathogenic pathways and identify therapeutic targets for human PD.
- Genome-wide P-element screen for Drosophila synaptogenesis mutants.
Liebl FL, Werner KM, Sheng Q, Karr JE, McCabe BD, Featherstone DE.
Journal of Neurobiology. 66: 332-47[+]A molecular understanding of synaptogenesis is a critical step toward the goal of understanding how brains "wire themselves up," and then "rewire" during development and experience. Recent genomic and molecular advances have made it possible to study synaptogenesis on a genomic scale. Here, we describe the results of a screen for genes involved in formation and development of the glutamatergic Drosophila neuromuscular junction (NMJ). We screened 2185 P-element transposon mutants representing insertions in approximately 16% of the entire Drosophila genome. We first identified recessive lethal mutants, based on the hypothesis that mutations causing severe disruptions in synaptogenesis are likely to be lethal. Two hundred twenty (10%) of all insertions were homozygous lethal. Two hundred five (93%) of these lethal mutants developed at least through late embryogenesis and formed neuromusculature. We examined embryonic/larval NMJs in 202 of these homozygous mutants using immunocytochemistry and confocal microscopy. We identified and classified 88 mutants with altered NMJ morphology. Insertion loci in these mutants encode several different types of proteins, including ATP- and GTPases, cytoskeletal regulators, cell adhesion molecules, kinases, phosphatases, RNA regulators, regulators of protein formation, transcription factors, and transporters. Thirteen percent of insertions are in genes that encode proteins of novel or unknown function. Complementation tests and RT-PCR assays suggest that approximately 51% of the insertion lines carry background mutations. Our results reveal that synaptogenesis requires the coordinated action of many different types of proteins--perhaps as much as 44% of the entire genome--and that transposon mutageneses carry important caveats that must be respected when interpreting results generated using this method.
- All neuropathies great and small.
Penny EB, McCabe BD.
Journal of Clinical Investigation 11:2968-71[+]Autosomal-dominant pure hereditary spastic paraplegia (AD-HSP) is characterized by the degeneration of long axons in corticospinal tracts and dorsal columns, resulting in spasticity and difficulty walking. Mutations in the SPG4 gene product spastin are the predominant genetic lesions associated with this inherited disease. In this issue, Orso et al. examine and reconcile existing Drosophila mutants of spastin and generate a new model for HSP by overexpression of a fly spastin transgene that carries a mutation prevalent in human AD-HSP (see the related article beginning on page 3026). Expression of this mutant spastin protein produces pathology in flies reminiscent of the human disease, including adult locomotion defects, in addition to causing aberrant synaptic morphology and altered microtubule stability. Both movement and synaptic defects in fly mutants were ameliorated by treatment with the microtubule-modifying agent vinblastine. The results are consistent with disease-causing mutations in human spastin producing dominant-negative proteins and confirm the usefulness of Drosophila genetic techniques to understand HSP and other neurodegenerative diseases.
- Highwire regulates presynaptic BMP signaling essential for synaptic growth.
McCabe BD*, Hom S, Aberle H, Fetter RD, Marques G, Haerry TE, Wan H, O'Connor MB, Goodman CS, Haghighi AP*.
Neuron. 25: 891-905.[+]Highwire (Hiw), a putative RING finger E3 ubiquitin ligase, negatively regulates synaptic growth at the neuromuscular junction (NMJ) in Drosophila. hiw mutants have dramatically larger synaptic size and increased numbers of synaptic boutons. Here we show that Hiw binds to the Smad protein Medea (Med). Med is part of a presynaptic bone morphogenetic protein (BMP) signaling cascade consisting of three receptor subunits, Wit, Tkv, and Sax, in addition to the Smad transcription factor Mad. When compared to wild-type, mutants of BMP signaling components have smaller NMJ size, reduced neurotransmitter release, and aberrant synaptic ultrastructure. BMP signaling mutants suppress the excessive synaptic growth in hiw mutants. Activation of BMP signaling, which in wild-type does not cause additional growth, in hiw mutants does lead to further synaptic expansion. These results reveal a balance between positive BMP signaling and negative regulation by Highwire, governing the growth of neuromuscular synapses. * corresponding
- Retrograde control of synaptic transmission by postsynaptic CaMKII at the Drosophila neuromuscular junction.
Haghighi AP, McCabe BD, Fetter RD, Palmer JE, Hom S, Goodman CS.
Neuron. 39: 255-67.[+]Retrograde signaling plays an important role in synaptic homeostasis, growth, and plasticity. A retrograde signal at the neuromuscular junction (NMJ) of Drosophila controls the homeostasis of neurotransmitter release. Here, we show that this retrograde signal is regulated by the postsynaptic activity of Ca2+/calmodulin-dependent protein kinase II (CaMKII). Reducing CaMKII activity in muscles enhances the signal and increases neurotransmitter release, while constitutive activation of CaMKII in muscles inhibits the signal and decreases neurotransmitter release. Postsynaptic inhibition of CaMKII increases the number of presynaptic, vesicle-associated T bars at the active zones. Consistently, we show that glutamate receptor mutants also have a higher number of T bars; this increase is suppressed by postsynaptic activation of CaMKII. Furthermore, we demonstrate that presynaptic BMP receptor wishful thinking is required for the retrograde signal to function. Our results indicate that CaMKII plays a key role in the retrograde control of homeostasis of synaptic transmission at the NMJ of Drosophila.
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- The BMP homolog Gbb provides a retrograde signal that regulates synaptic growth at the Drosophila neuromuscular junction.
McCabe BD*, Marqués G, Haghighi AP, Fetter RD, Crotty ML, Haerry TE, Goodman CS, O'Connor MB*.
Neuron. 39: 241-54.[+]We show that the BMP ortholog Gbb can signal by a retrograde mechanism to regulate synapse growth of the Drosophila neuromuscular junction (NMJ). gbb mutants have a reduced NMJ synapse size, decreased neurotransmitter release, and aberrant presynaptic ultrastructure. These defects are similar to those we observe in mutants of BMP receptors and Smad transcription factors. However, whereas these BMP receptors and signaling components are required in the presynaptic motoneuron, Gbb expression is required in large part in postsynaptic muscles; gbb expression in muscle rescues key aspects of the gbb mutant phenotype. Consistent with this notion, we find that blocking retrograde axonal transport by overexpression of dominant-negative p150/Glued in neurons inhibits BMP signaling in motoneurons. These experiments reveal that a muscle-derived BMP retrograde signal participates in coordinating neuromuscular synapse development and growth. * corresponding
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