127 research outputs found
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Acute activation of conserved synaptic signaling pathways in Drosophila melanogaster
No full textStudies of memory have identified several memory classifications: declarative, implicit, working, and anesthesia-resistant. One simple classification that may be applied to the array of model systems now used to explore memory is the requirement for de novo gene expression and protein synthesis for the formation of long-term memory (LTM). Short-term memory (STM) appears to require the modification of pre-existing neuronal molecules and is resistant to inhibitors of protein synthesis. These molecules, believed to encode proteins that effect long-lasting neuronal changes likely at the level of the synapse, are manifested behaviorally as memory. Neural activity regulates the cellular decision to synthesize these molecules, yet the identity and function of these molecules are largely unknown. What is known has largely been elucidated by work in mollusks and vertebrates in which procedures have been developed to generate neural activity sufficient to induce long-lasting, protein synthesis-dependent neuronal plasticity. Using these procedures, several key intracellular signaling pathways (Ras/ERK, cAMP/PKA) and important early gene products (arc, zif268, AP1) critical to memory have been identified. Similar procedures are not presently available in Drosophila. Establishing these procedures would greatly enhance the Drosophila model system for identification of plasticity molecules and mechanisms that control their expression. We have explored the potential of conditional Drosophila seizure mutants of comatose and CaP60A mutants for the development of a neural activity generation paradigm capable of (1) inducing long lasting and robust neural activity; (2) acute and persistent activation of the ERK signaling pathway and induction of Drosophila homologs of immediate early genes known to be involved in plasticity; (3) alteration of synaptic localization of fasciclin II, a known effector of synaptic plasticity. Using these mutants, we have established the conservation in insects of a known neural activity regulated signaling pathway shown to be critical to both long term plasticity and memory. Secondly, we have identified a central role for AP1, a classical activity induced gene, in regulating Drosophila neural plasticity. The neural activity paradigm coupled with the identification AP1 dual control of both major branches of long term neuronal change, structural and functional plasticity, provides researchers valuable tools for addressing some the outstanding questions facing the plasticity field today
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Genetic analysis of endocytosis at the Drosophila synapse
No full textEndocytosis plays an essential role in maintaining a pool of synaptic vesicles for sustained neurotransmitter release. Synaptic vesicles are internalized and fuse with endosomes, and are subsequently reassembled to be ready for another round of exocytosis. Here I describe in two distinct studies the function of endosomes at synapses and regulation of dynamin, a protein essential for endocytosis, using the Drosophila synapse as a model. To study the function of endosomes at synapses I analyzed the localization and function of two Drosophila endosomal proteins, Hook and Deep orange (Dor), at the larval neuromuscular junction. I present here the first genetic evidence of a role for endocytic trafficking in plasticity of the synapse. I also found that mutations in hook and dor affect the number of varicosities at the nerve terminal without affecting synaptic vesicle recycling, indicating that Hook and Dor proteins play a role in later stages of endocytosis at the synapse. Dynamin is a GTPase that is essential for internalization of synaptic vesicles from the plasma membrane. Flies carrying shi ts mutations have a conditional defect in dynamin function. Molecules that regulate GTP loading (guanine-nucleotide exchange factors-GEFs) and GTPase activity (GTPase activating proteins-GAPs) of dynamin are unknown. Here I describe the identification of such molecules/domains by analyses of enhancer and suppressor mutations identified in previously conducted genetic screens. I show here that the enzymatic activity of Nucleoside diphosphate kinase (NDP Kinase), a source of GTP encoded by the Drosophila abnormal wing discs (awd) or human nm23 tumor suppressor genes, is essential for dynamin function at synapses. Dynamin is also regulated by an intramolecular GTPase effector domain (GED) and I have identified separate mutations in shi, which map to the GED, that suppress endocytic defects in shits2. Overall, these data indicate a model in which the stability of dynamin: GTP is opposingly regulated by an unusual GEF activity of NDP kinase and a GAP activity in dynamin; in addition these findings indicate the possibility of an intriguing therapy for nm23 tumor progression
Investigating mechanisms underlying olfactory habituation in Drosophila melanogaster
No full textTHESIS 8898Habituation is a common form of learning and memory that has been poorly studied
despite its fundamental importance and clinical significance. During habituation, the
behavioural response to a prolonged or repeated unreinforced stimulus is attenuated.
Drosophila melanogaster is a particularly useful model system in which to study
olfactory habituation, due to the well-understood olfactory circuitry and availability of a wide array of genetic tools
Olfactory-avoidance habituation in Drosophila melanogaster
No full textTHESIS 11028Habituation is a form of sensory filtering in response to prolonged or repeated stimuli in the environment [Harris, 1943; Thompson and Spencer, 1966; Christoffersen, 1997; Rankin et al., 2009], It provides biological organisms with a means of ignoring non-salient aspects of the local environment in order to selectively focus on stimuli that are potentially more relevant e.g. those associated with danger or a food source. Though habituation is one of the simplest form of memory, it is likely an important building block for more complex forms of learning [Fabiani et al., 2006; Rankin et al., 2009]
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No full textBehavioral adaptation to environmental threats and subsequent social transmission of adaptive behavior has evolutionary implications. In Drosophila, exposure to parasitoid wasps leads to a sharp decline in oviposition. We show that exposure to predator elicits both an acute and learned oviposition depression, mediated through the visual system. However, long-term persistence of oviposition depression after predator removal requires neuronal signaling functions, a functional mushroom body, and neurally driven apoptosis of oocytes through effector caspases. Strikingly, wasp-exposed flies (teachers) can transmit egg-retention behavior and trigger ovarian apoptosis in naive, unexposed flies (students). Acquisition and behavioral execution of this socially learned behavior by naive flies requires all of the factors needed for primary learning. The ability to teach does not require ovarian apoptosis. This work provides new insight into genetic and physiological mechanisms that underlie an ecologically relevant form of learning and mechanisms for its social transmission
Network Plasticity in Adaptive Filtering and Behavioral Habituation
No full textThe ability of organisms to seamlessly ignore familiar, inconsequential stimuli improves their selective attention and response to salient features of the environment. Here, I propose that this fundamental but unexplained phenomenon substantially derives from the ability of any pattern of neural excitation to create an enhanced inhibitory (or “negative”) image of itself through target-specific scaling of inhibitory inputs onto active excitatory neurons. Familiar stimuli encounter strong negative images and are therefore less likely to be transmitted to higher brain centers. Integrating historical and recent observations, the negative-image model described here provides a mechanistic framework for understanding habituation, which is connected to ideas on dynamic predictive coding. In addition, it suggests insights for understanding autism spectrum disorders.Video Abstrac
Plasticity of recurrent inhibition in the Drosophila antennal lobe
No full textRecurrent inhibition, wherein excitatory principal neurons stimulate inhibitory interneurons that feedback on the same principal cells,
occurs ubiquitously in the brain. However, the regulation and function of recurrent inhibition are poorly understood in terms of the
contributing interneuron subtypes as well as their effect on neural and cognitive outputs. In the
Drosophila
olfactory system, odorants
activate olfactory sensory neurons (OSNs), which stimulate projection neurons (PNs) in the antennal lobe. Both OSNs and PNs activate
localinhibitoryneurons(LNs)thatprovideeitherfeedforwardorrecurrent/feedbackinhibitioninthelobe.Duringolfactoryhabituation,
prior exposure to an odorant selectively decreases the animal?s subsequent response to the odorant. We show here that habituation
occursinresponsetofeedbackfromPNs.OutputfromPNsisnecessaryforolfactoryhabituationand,intheabsenceofodorant,directPN
activation is sufficient to induce the odorant-selective behavioral attenuation characteristic of olfactory habituation. PN-induced habit-
uation occludes further odor-induced habituation and similarly requires GABA
A
Rs and NMDARs in PNs, as well as VGLUT and cAMP
signaling in the multiglomerular inhibitory local interneurons (LN1) type of LN. Thus, PN output is monitored by an LN subtype whose
resultant plasticity underlies behavioral habituation. We propose that recurrent inhibitory motifs common in neural circuits may
similarly underlie habituation to other complex stimul
Molecular genetic studies on voltage-gated ion channels
No full textSeveral different methods have been employed in the study of voltage-gated ion
channels. Electrophysiological studies on excitable cells in vertebrates and molluscs have
shown that many different voltage-gated potassium (K+) channels and sodium channels
may coexist in the same organism. Parallel genetic studies in Drosophila have identified
mutations in several genes that alter the properties of specific subsets of physiologically
identified ion channels. Chapter 2 describes molecular studies that identify two Drosophila
homologs of vertebrate sodium-channel genes. Mutations in one of these Drosophila
sodium-channel genes are shown to be responsible for the temperature-dependent paralysis
of a behavioural mutant parats. Evolutionary arguments, based on the partial sequences of
the two Drosophila genes, suggest that subfamilies of voltage-gated sodium channels in
vertebrates remain to be identified.
In Drosophila, diverse voltage-gated K+ channels arise from alternatively spliced
mRNAs generated at the Shaker locus. Chapter 3 and the Appendices describe the isolation
and characterization of several human K+-channel genes, similar in sequence to Shaker.
Each of these human genes has a highly conserved homolog in rodents; thus, this K+-channel
gene family probably diversified prior to the mammalian radiation. Functional K+
channels encoded by these genes have been expressed in Xenopus oocytes and their
properties have been analyzed by electrophysiological methods. These studies demonstrate
that both transient and noninactivating voltage-gated K+ channels may be encoded by
mammalian genes closely related to Shaker. In addition, results presented in Appendix 3
clearly demonstrate that independent gene products from two K+-channel genes may
efficiently co-assemble into heterooligomeric K+ channels with properties distinct from
either homomultimeric channel. This finding suggests yet another molecular mechanism for
the generation of K+-channel diversity.</p
A new genetic model of activity-induced Ras signaling dependent pre-synaptic plasticity in Drosophila
No full textTechniques to induce activity-dependent neuronal plasticity in vivo allow the underlying signaling pathways to be studied in their biological context. Here, we demonstrate activity-induced plasticity at neuromuscular synapses of Drosophila double mutant for comatose (an NSF mutant) and Kum (a SERCA mutant), and present an analysis of the underlying signaling pathways. comt; Kum (CK) double mutants exhibit increased locomotor activity under normal culture conditions, concomitant with a larger neuromuscular junction synapse and stably elevated evoked transmitter release. The observed enhancements of synaptic size and transmitter release in CK mutants are completely abrogated by: a) reduced activity of motor neurons; b) attenuation of the Ras/ERK signaling cascade; or c) inhibition of the transcription factors Fos and CREB. all of which restrict synaptic properties to near wild type levels. Together, these results document neural activity-dependent plasticity of motor synapses in CK animals that requires Ras/ERK signaling and normal transcriptional activity of Fos and CREB. Further, novel in vivo reporters of neuronal Ras activation and Fos transcription also confirm increased signaling through a Ras/AP-1 pathway in motor neurons of CK animals, consistent with results from our genetic experiments. Thus, this study: a) provides a robust system in which to study activity-induced synaptic plasticity in vivo; b) establishes a causal link between neural activity, Ras signaling, transcriptional regulation and pre-synaptic plasticity in glutamatergic motor neurons of Drosophila larvae; and c) presents novel, genetically encoded reporters for Ras and AP-1 dependent signaling pathways in Drosophila
Altered ribostasis: RNA-protein granules in degenerative disorders
No full textThe molecular processes that contribute to degenerative diseases are not well understood. Recent observations suggest that some degenerative diseases are promoted by the accumulation of nuclear or cytoplasmic RNA-protein (RNP) aggregates, which can be related to endogenous RNP granules. RNP aggregates arise commonly in degenerative diseases because RNA-binding proteins commonly self-assemble, in part through prion-like domains, which can form self-propagating amyloids. RNP aggregates may be toxic due to multiple perturbations of posttranscriptional control, thereby disrupting the normal "ribostasis" of the cell. This suggests that understanding and modulating RNP assembly or clearance may be effective approaches to developing therapies for these diseases
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