Current Search: Murphey, Rodney (x)
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- Title
- Frazzled and netrin: a story of neuronal confusion and competition in the drosophila giant fiber system.
- Creator
- Orr, Brian, Murphey, Rodney K., Graduate College
- Date Issued
- 2011-04-08
- PURL
- http://purl.flvc.org/fcla/dt/3164669
- Subject Headings
- Neural circuitry, Drosophila, Synapses
- Format
- Document (PDF)
- Title
- The PHR proteins: intracellular signaling hubs in neuronal development and axon degeneration.
- Creator
- Grill, Brock, Murphey, Rodney K., Borgen, Melissa A.
- Abstract/Description
-
During development, a coordinated and integrated series of events must be accomplished in order to generate functional neural circuits. Axons must navigate toward target cells, build synaptic connections, and terminate outgrowth. The PHR proteins (consisting of mammalian Phr1/MYCBP2, Drosophila Highwire and C. elegans RPM-1) function in each of these events in development. Here, we review PHR function across species, as well as the myriad of signaling pathways PHR proteins regulate. These...
Show moreDuring development, a coordinated and integrated series of events must be accomplished in order to generate functional neural circuits. Axons must navigate toward target cells, build synaptic connections, and terminate outgrowth. The PHR proteins (consisting of mammalian Phr1/MYCBP2, Drosophila Highwire and C. elegans RPM-1) function in each of these events in development. Here, we review PHR function across species, as well as the myriad of signaling pathways PHR proteins regulate. These findings collectively suggest that the PHR proteins are intracellular signaling hubs, a concept we explore in depth. Consistent with prominent developmental functions, genetic links have begun to emerge between PHR signaling networks and neurodevelopmental disorders, such as autism, schizophrenia and intellectual disability. Finally, we discuss the recent and important finding that PHR proteins regulate axon degeneration, which has further heightened interest in this fascinating group of molecules.
Show less - Date Issued
- 2016-12-23
- PURL
- http://purl.flvc.org/fau/fd/FAUIR000039
- Format
- Citation
- Title
- Netrin-Frazzled signaling instructs synaptogenesis and plasticity at an identified central synapse in Drosophila.
- Creator
- Orr, Brian, Murphey, Rodney K., Charles E. Schmidt College of Science, Department of Biological Sciences
- Abstract/Description
-
The classic guidance molecules, Netrin and its receptor Frazzled (Fra), dictate the strength of synaptic connections in the giant fiber system (GFS) of Drosophila melanogaster by regulating gap junction localization in the pre-synaptic terminal. In Netrin mutant animals the synaptic coupling between a giant interneuron and the jump motor neuron was weakened. Dye-coupling between these two neurons was severely compromised or absent. These mutants exhibited anatomically and physiologically...
Show moreThe classic guidance molecules, Netrin and its receptor Frazzled (Fra), dictate the strength of synaptic connections in the giant fiber system (GFS) of Drosophila melanogaster by regulating gap junction localization in the pre-synaptic terminal. In Netrin mutant animals the synaptic coupling between a giant interneuron and the jump motor neuron was weakened. Dye-coupling between these two neurons was severely compromised or absent. These mutants exhibited anatomically and physiologically defective synapses between the giant fiber (GF) and tergotrochanteral motor neuron (TTMn). In cases where Netrin mutants displayed apparently normal synaptic anatomy, half of the specimens exhibited physiologically defective synapses. Dye-coupling between the giant fiber and the motor neuron was reduced or eliminated, suggesting that gap junctions were disrupted in the Netrin mutants. When we examined the gap junctions with antibodies to Shaking-B Innexin (ShakB), they were significantly decreased or absent in the pre-synaptic terminal of the mutant GF. This data is the first to show that Netrin and Frazzled regulate placement of gap junctions pre-synaptically at a central synapse. In the Drosophila Giant Fiber System, we demonstrate a mechanism that ensures the monoinnervation of two homologous motor neurons by two homologous interneurons. In a scenario where both interneurons could synapse with both motor neuron targets, each interneuron exclusively synapsed with only one target and the circuit functions at normal physiological levels. This innervation pattern depended on the ratio of netrin-to-frazzled expression. When Netrin was over expressed in the system, shifting the ratio in favor of Netrin, both interneurons synapsed with both target motor neurons and physiological function was reduced. This resulted in the polyinnervationof a single target. In contrast, when Frazzled was over expressed in the system, one interneuron innervated both targets and excluded the remaining interneuron from making any synaptic contact. This resulted in a single interneuron mono-innervating both motor neurons and physiological function was mutant. The orphaned interneuron made no synaptic contact with either motor neuron target. Physiological function was only normal when the Netrin-Frazzled ratio was at endogenous levels and each GF monoinnervated one motor neuron. When we examined the gap junctions at this synapse in experimental animals, there was a significant reduction of gap junction hemichannels in the presynaptic terminal of axons that deviated from normal innervation patterns. While the synapse dyecoupled, the reduction in gap junction hemichannels reduced function in the circuit.
Show less - Date Issued
- 2013
- PURL
- http://purl.flvc.org/fau/fd/FA0004041
- Subject Headings
- Cellular control mechanisms, Cellular signal transduction, Drosophila melanogaster -- Cytogenetics, Genetic transcription, Transcription factors
- Format
- Document (PDF)
- Title
- Frazzled’s Role in Synapse Formation at a Drosophila Giant Synapse.
- Creator
- Lopez, Juan, Murphey, Rodney K., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Biological Sciences
- Abstract/Description
-
In Drosophila melanogaster, the GFS is synaptically coupled to the Tergotrochanteral motoneurons; these neurons form a signaling pathway from the brain to the jump muscles (Thomas and Wyman, 1983). Part of this signaling is done through gap junctions, and placement of these gap junctions was partially shown to be regulated by the binding of Netrin, a class of guidance molecule (Orr et al., 2014). In the present study we investigate the role of Netrin's receptor Frazzled in the placement of...
Show moreIn Drosophila melanogaster, the GFS is synaptically coupled to the Tergotrochanteral motoneurons; these neurons form a signaling pathway from the brain to the jump muscles (Thomas and Wyman, 1983). Part of this signaling is done through gap junctions, and placement of these gap junctions was partially shown to be regulated by the binding of Netrin, a class of guidance molecule (Orr et al., 2014). In the present study we investigate the role of Netrin's receptor Frazzled in the placement of gap junctions in Drosophila at: 1) Presynaptic neurons (Giant Fibers [GF]), 2) Postsynaptic neurons (Tergotrochanteral motoneurons [TTMn]), and 3) Presynaptic + Postsynaptic neurons simultaneously. Effects of Frazzled were tested using Frazzled RNAi and a combination of electrophysiological recordings and imaging of the GF-TTMn synapse. The results from this study show that presynaptic and postsynaptic knockdown of Frazzled delayed muscular responses and altered the anatomy of both the GF's and TTMn's.
Show less - Date Issued
- 2018
- PURL
- http://purl.flvc.org/fau/fd/FA00013085
- Subject Headings
- Drosophila melanogaster--Nervous system., Gap Junctions., Synapses., Netrin Receptors.
- Format
- Document (PDF)
- Title
- HISTAMINERGIC AND NOCICEPTIVE GROOMING IN DROSOPHILA MELANOGASTER: AN ANALYSIS OF THE MOLECULAR MECHANISMS AND A BEHAVIORAL RESPONSE TO NOXIOUS CHEMICAL STIMULI.
- Creator
- John, Ciny, Dawson-Scully, Ken, Murphey, Rodney, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Biological Sciences
- Abstract/Description
-
Insect grooming has various functions, including defense against parasites and pathogens, cleaning of dust particles, and maintenance of sensory receptors. The hierarchy of grooming behavior suggests that cleaning one body part is more crucial than the other, the priority order more specifically being eyes, antennae, abdomen, then wings, followed by the thorax. Histamine is an extensively studied neurotransmitter found in the central nervous system of many animals. In Drosophila, histamine is...
Show moreInsect grooming has various functions, including defense against parasites and pathogens, cleaning of dust particles, and maintenance of sensory receptors. The hierarchy of grooming behavior suggests that cleaning one body part is more crucial than the other, the priority order more specifically being eyes, antennae, abdomen, then wings, followed by the thorax. Histamine is an extensively studied neurotransmitter found in the central nervous system of many animals. In Drosophila, histamine is found in both the peripheral and central nervous systems and is necessary for visual and mechanosensory behaviors. Histamine-gated chloride channel 1 (HisCl1) and Ora transientless (Ort) are two characterized histamine receptors, both of which are vital for visual signaling in the fly.
Show less - Date Issued
- 2019
- PURL
- http://purl.flvc.org/fau/fd/FA00013321
- Subject Headings
- Drosophila melanogaster, Grooming behavior in animals, Nociception, Histaminergic mechanisms
- Format
- Document (PDF)
- Title
- Synaptic Rearrangements and the Role of Netrin-Frazzled Signaling in Shaping the Drosophila Giant Fiber Circuit.
- Creator
- Lloyd, Brandon N., Murphey, Rodney K., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Biological Sciences
- Abstract/Description
-
In the developing CNS, presynaptic neurons often have exuberant overgrowth and form excess (and overlapping) postsynaptic connections. Importantly, these excess connections are refined during circuit maturation so that only the appropriate connections remain. This synaptic rearrangement phenomenon has been studied extensively in vertebrates but many of those models involve complex neuronal circuits with multiple presynaptic inputs and postsynaptic outputs. Using a simple escape circuit in...
Show moreIn the developing CNS, presynaptic neurons often have exuberant overgrowth and form excess (and overlapping) postsynaptic connections. Importantly, these excess connections are refined during circuit maturation so that only the appropriate connections remain. This synaptic rearrangement phenomenon has been studied extensively in vertebrates but many of those models involve complex neuronal circuits with multiple presynaptic inputs and postsynaptic outputs. Using a simple escape circuit in Drosophila melanogaster (the giant fiber circuit), we developed tools that enabled us to study the molecular development of this circuit; which consists of a bilaterally symmetrical pair of presynaptic interneurons and postsynaptic motorneurons. In the adult circuit, each presynaptic interneuron (giant fiber) forms a single connection with the ipsilateral, postsynaptic motorneuron (TTMn). Using new tools that we developed we labeled both giant fibers throughout their development and saw that these neurons overgrew their targets and formed overlapping connections. As the circuit matured, giant fibers pruned their terminals and refined their connectivity such that only a single postsynaptic connection remained with the ipsilateral target. Furthermore, if we ablated one of the two giant fibers during development in wildtype animals, the remaining giant fiber often retained excess connections with the contralateral target that persisted into adulthood. After demonstrating that the giant fiber circuit was suitable to study synaptic rearrangement, we investigated two proteins that might mediate this process. First, we were able to prevent giant fibers from refining their connectivity by knocking out highwire, a ubiquitin ligase that prevented pruning. Second, we investigated whether overexpressing Netrin (or Frazzled), part of a canonical axon guidance system, would affect the refinement of giant fiber connectivity. We found that overexpressing Netrin (or Frazzled) pre- & postsynaptically resulted in some giant fibers forming or retaining excess connections, while exclusively presynaptic (or postsynaptic) expression of either protein had no effect. We further showed that by simultaneously reducing (Slit-Robo) midline repulsion and elevating Netrin (or Frazzled) pre- & postsynaptically, we significantly enhanced the proportion of giant fibers that formed excess connections. Our findings suggest that Netrin-Frazzled and Slit-Robo signaling play a significant role in refining synaptic circuits and shaping giant fiber circuit connectivity.
Show less - Date Issued
- 2016
- PURL
- http://purl.flvc.org/fau/fd/FA00004758, http://purl.flvc.org/fau/fd/FA00004758
- Subject Headings
- Drosophila melanogaster--Cytogenetics., Genetic transcription., Transcription factors., Cellular signal transduction., Cellular control mechanisms., Cell receptors.
- Format
- Document (PDF)
- Title
- Highwire coordinates synapse formation and maturation by regulating both a map kinase cascade and the ability of the axon to respond to external cues in the giant fiber system of Drosophila Melanogaster.
- Creator
- Borgen, Melissa A., Murphey, Rodney K., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Biological Sciences
- Abstract/Description
-
The ubiquitin ligase Highwire is responsible for cell-autonomously promoting synapse formation in the Drosophila Giant Fiber system. highwire mutants show defects in synaptic function and extra branching at the axon terminal, corresponding to transient branching that occur in the course of giant synapse formation during metamorphosis. The MAP kinase pathway, including Wallenda and JNK/Basket, plus the transcription factor Jun, act to suppress synaptic function and axon pruning in a dosage...
Show moreThe ubiquitin ligase Highwire is responsible for cell-autonomously promoting synapse formation in the Drosophila Giant Fiber system. highwire mutants show defects in synaptic function and extra branching at the axon terminal, corresponding to transient branching that occur in the course of giant synapse formation during metamorphosis. The MAP kinase pathway, including Wallenda and JNK/Basket, plus the transcription factor Jun, act to suppress synaptic function and axon pruning in a dosage sensitive manner, suggesting different molecular mechanisms downstream of the MAP kinase pathway govern function and pruning. A novel role for Highwire is revealed, regulating the giant fiber axon’s ability to respond to external cues regulated by Fos. When expression of the transcription factor Fos is disrupted in the post-synaptic TTMn or surrounding midline glia of highwire mutants, the giant fiber axons show a marked increase in axon overgrowth and midline crossing. However, synaptic function is rescued by the cell nonautonomous manipulation of Fos, indicating distinct mechanisms downstream of Highwire regulating synaptic function and axon morphology.
Show less - Date Issued
- 2014
- PURL
- http://purl.flvc.org/fau/fd/FA00004081, http://purl.flvc.org/fau/fd/FA00004081
- Subject Headings
- Cell differentiation, Cellular control mechanisms, Cellular signal transduction, Drosophila melanogaster -- Cytogenetics, Gene expression, Genetic transcription
- Format
- Document (PDF)
- Title
- FRAZZLED/DCC REGULATES SYNAPTOGENESIS AT A DROSOPHILA GIANT SYNAPSE.
- Creator
- Lopez, Juan, Murphey, Rodney, Florida Atlantic University, Department of Biological Sciences, Charles E. Schmidt College of Science
- Abstract/Description
-
Synaptogenesis is a requirement for cellular communication, but the specific molecular mechanisms underlying synaptogenesis are unclear. Here, we investigate and show the role of the protein Frazzled in synaptogenesis using the transheterozygous Frazzled loss-of-function (LOF) mutant in Drosophila. Leveraging the UAS-GAL4 expression system, we drove expression of various Frazzled/DCC gene constructs in the Giant Fibers (GF) of flies and found changes to synaptogenesis and axon pathfinding. We...
Show moreSynaptogenesis is a requirement for cellular communication, but the specific molecular mechanisms underlying synaptogenesis are unclear. Here, we investigate and show the role of the protein Frazzled in synaptogenesis using the transheterozygous Frazzled loss-of-function (LOF) mutant in Drosophila. Leveraging the UAS-GAL4 expression system, we drove expression of various Frazzled/DCC gene constructs in the Giant Fibers (GF) of flies and found changes to synaptogenesis and axon pathfinding. We identified decreases in electrical synaptogenesis and distinct axon pathfinding errors in Frazzled LOF mutants. Strikingly, the expression of Frazzled intracellular domain (ICD) significantly rescues both phenotypes, while full-length Frazzled protein only partially rescues these phenotypes, prompting us to explore the role of different domains within the protein. Deleting the P1 and P2 domains of Frazzled does not rescue axon pathfinding but did partially rescue synaptogenesis while deleting the P3 domain failed to rescue either phenotype. Moreover, when we drive expression Frazzled with a point-mutated P3 domain, silencing its transcriptional activation domain, it fails to rescue both synaptogenesis and axon pathfinding. These results strongly suggest that Frazzled regulates both synaptogenesis and axon pathfinding in the GFs and is necessary for synaptogenesis of the mixed electrochemical GF synapse. Our results provide novel insights into the molecular mechanisms governing neural circuit assembly and highlight Frazzled as a key player in axon guidance and synaptic development.
Show less - Date Issued
- 2023
- PURL
- http://purl.flvc.org/fau/fd/FA00014310
- Subject Headings
- Drosophila, Synapses, Gap Junctions, Receptors, Cell Surface
- Format
- Document (PDF)
- Title
- Dscam1 Regulates Synapse Formation and Function in the Giant Fiber System of Drosophila.
- Creator
- Spencer, Casey L., Murphey, Rodney, Florida Atlantic University, Department of Biological Sciences, Charles E. Schmidt College of Science
- Abstract/Description
-
Proper formation of synapses in the developing nervous system is critical to the expected function and behavior of an adult organism. Neurons must project neurites, in the form of axons or dendrites, to target areas to complete synaptic circuits. The biochemical tool that cells use to interact with the external environment and direct the guidance of developing neurites are guidance receptors. One such guidance receptor that is extensively studied to uncover its roles in developmental...
Show moreProper formation of synapses in the developing nervous system is critical to the expected function and behavior of an adult organism. Neurons must project neurites, in the form of axons or dendrites, to target areas to complete synaptic circuits. The biochemical tool that cells use to interact with the external environment and direct the guidance of developing neurites are guidance receptors. One such guidance receptor that is extensively studied to uncover its roles in developmental disorders and disease is DSCAM (Down-Syndrome Cell Adhesion Molecule). To better understand the role of DSCAM in humans, a fly homolog Dscam1 was extensively characterized in the giant fiber system (GFS) of Drosophila to further explore its roles in axon guidance, synapse formation, and synapse function. The UAS-Gal4 system was used to alter the protein levels of Dscam1 within the giant fiber interneurons (GFs). A UAS-RNAi construct against Dscam1 was used to knockdown translation of all possible isoforms within the GFs. A UAS-Dscam1(TM2) construct was used to overexpress a single isoform of Dscam1 that is specifically trafficked to the axons. Confocal microscopy was used to determine the morphological changes associated with dysregulated Dscam1 levels. Visualization via fluorescent markers was accomplished of both pre- and post-synaptic cells, the GFs and tergotrochanteral motorneurons (TTMns), respectively, and synapse interface was determined as colocalization of the two cells. Additionally, the functional components of the GF-TTMn synapse, both gap-junctions, and presynaptic chemical active zones were tagged via fluorescent antibodies and quantified.
Show less - Date Issued
- 2023
- PURL
- http://purl.flvc.org/fau/fd/FA00014364
- Subject Headings
- Drosophila, Cell Adhesion Molecules, Nervous System, Synapses
- Format
- Document (PDF)
- Title
- ESTABLISHMENT AND APPLICATION OF WORKFLOWS FOR STRUCTURE-FUNCTION ANALYSIS OF SYNAPTIC COMPONENTS.
- Creator
- Thomas, Connon I., Kamasawa, Naomi, Murphey, Rodney, Florida Atlantic University, Department of Biological Sciences, Charles E. Schmidt College of Science
- Abstract/Description
-
At the site of neuronal communication, multiple interacting components drive synapse structure and function. Synaptic vesicle pools, membrane proteins, mitochondria, and perisynaptic astrocyte processes (PAPs) are all structures that can be altered through naturally occurring plasticity mechanisms to modulate neurotransmission, and disruption of these structures can result in synapse dysfunction and disease. Due to the minute size of the synapse, electron microscopy (EM) remains the gold...
Show moreAt the site of neuronal communication, multiple interacting components drive synapse structure and function. Synaptic vesicle pools, membrane proteins, mitochondria, and perisynaptic astrocyte processes (PAPs) are all structures that can be altered through naturally occurring plasticity mechanisms to modulate neurotransmission, and disruption of these structures can result in synapse dysfunction and disease. Due to the minute size of the synapse, electron microscopy (EM) remains the gold standard for ultrastructural characterization; however, due to the complexity of EM datasets, extraction of information has become a bottleneck which places limits on the amount of data that can be collected and analyzed. A need exists for easy-to-use workflows that automate and enhance analysis throughput, to keep up with the streams of image data that are able to be produced. Here, I develop the use of AI algorithms, correlative microscopy techniques, and novel structural analysis methods to characterize postsynaptic mitochondria, PAPs, synaptic vesicles, and integral membrane proteins and their impact on synapse structure and function. I show that both postsynaptic mitochondria and PAPs in the visual cortex are positioned to support synapse structure and function; cleavage of a synaptic adhesion molecule affects synaptic vesicle accumulation in the amygdala; and presynaptic voltage gated calcium channels aggregate near active zone machinery in the brainstem. In addition, I highlight the use of virtual reality as a fast and intuitive tool for the identification and isolation of individual neurites in 3D EM. Thus, my work establishes novel technical approaches for EM and advances our understanding of neuronal communication through original research of several synaptic components.
Show less - Date Issued
- 2023
- PURL
- http://purl.flvc.org/fau/fd/FA00014315
- Subject Headings
- Synapses, Artificial intelligence, Astrocytes
- Format
- Document (PDF)