22 research outputs found
The Role of Cytoskeletal Stability in Regulating Synapse Development and Axonal Regeneration through the DLK Pathway
No full textProper network information processing relies on the intact axonal and synaptic function. In this work we investigate the mechanisms regulating the formation of the synapse and axonal response to injury.
During development, neurons send out axons to connect them to their distal targets. The formation of the synapse, a point of contact between the two functional units of the nervous system, is regulated by an array of genes, many of which remain unknown. Through a large-scale RNAi screen we have identified a large number of novel genes that are involved in regulating different aspects of synapse development. By separating the genes based on their function and correlating them to the phenotype that they cause we have identified a number of genes with a shared function that are involved in a particular aspect of synapse development. Notably, genes for proteasome subunits and mitotic spindle organizers are enriched in those causing defects in synaptic apposition and NMJ stability.
Genes that are involved in synapse development often also play a role in other aspects of neuronal function. We pursued the function of one particular gene that is involved in synapse development, short stop. We identify a novel allele of short stop which does not cause embryonic lethality and allows us to study the role that short stop plays in synaptic development. Mutants for short stop have a striking synapse overgrowth. This synapse phenotype is caused by the upregulation of the dual leucine zipper kinase (DLK) pathway, a MAP3K known for its role in synapse development and axon regeneration. We hypothesize that the molecular function of Short Stop as an actin-microtubule cross-linker is responsible for the DLK pathway activation in the mutant. To support this model we demonstrate that knock down of the subunits of the TCP1 complex, a chaperonin that folds actin and microtubules, also results in the upregulation of the DLK pathway. These data lead us to propose that cytoskeleton destabilization is a mechanism of DLK pathway activation. We further show that activation of this pathway in the short stop mutant is sufficient to enhance axonal response to injury.
Although the DLK pathway is a key regulator of the axonal injury response, it is still unclear how this pathway is activated during injury. We demonstrate that the DLK pathway can be activated by pharmacological disruption of the cytoskeleton, which also happens during a traumatic injury. This new mechanism allows us to manipulate the DLK pathway in the intact neuron and test the sufficiency of this pathway in axonal regeneration response. We show that activating the DLK pathway via pharmacological destabilization of the cytoskeleton is sufficient to enhance axonal regeneration after injury. These data establish a new mechanism of the DLK pathway activation and that the DLK pathway is not only required but also sufficient to turn on a pro-regenerative state in an uninjured neuron
Excitatory/Inhibitory Balance and Circuit Homeostasis in Autism Spectrum Disorders
No full textAutism spectrum disorders (ASDs) and related neurological disorders are associated with mutations in many genes affecting the ratio between neuronal excitation and inhibition. However, understanding the impact of these mutations on network activity is complicated by the plasticity of these networks, making it difficult in many cases to separate initial deficits from homeostatic compensation. Here we explore the contrasting evidence for primary defects in inhibition or excitation in ASDs and attempt to integrate the findings in terms of the brain’s ability to maintain functional homeostasis
Intracellular Recordings of Postsynaptic Voltage Responses at the Drosophila Neuromuscular Junction
No full textInfluence of phonon dispersion on exciton damping in ionic crystals
No full textThe manifestation of phonon dispersion on frequency and temperature dependence of exciton damping is investigated theoretically for the models of crystal with the large and small exciton radii. The correlation between the dispersion and the frequency intervals with phonon absorption and emission is discussed for the exciton of TlBr, ZnS and some other crystals as examples. It is demonstrated that depending on frequency the dispersion results both in increase and reduction of the exciton damping. In addition, the intensity of exciton damping close to the peaks of phonon absorption and emission is varied. The change of the tendency of influence of dispersion on damping for some fixed frequency with temperature growing is noticed.The author expresses gratitude to Profs М.P. Lysytsja, М.Уa. Valakh and Dr А.М. Уaremko for helpful discussions of the work results
Influence of phonon dispersion on exciton damping in ionic crystals
No full textThe manifestation of phonon dispersion on frequency and temperature dependence of exciton damping is investigated theoretically for the models of crystal with the large and small exciton radii. The correlation between the dispersion and the frequency intervals with phonon absorption and emission is discussed for the exciton of TlBr, ZnS and some other crystals as examples. It is demonstrated that depending on frequency the dispersion results both in increase and reduction of the exciton damping. In addition, the intensity of exciton damping close to the peaks of phonon absorption and emission is varied. The change of the tendency of influence of dispersion on damping for some fixed frequency with temperature growing is noticed.The author expresses gratitude to Profs М.P. Lysytsja, М.Уa. Valakh and Dr А.М. Уaremko for helpful discussions of the work results
A large-scale RNAi screen identifies functional classes of genes shaping synaptic development and maintenance
No full textAbstractNeuronal circuit development and function require proper synapse formation and maintenance. Genetic screens are one powerful method to identify the mechanisms shaping synaptic development and stability. However, genes with essential roles in non-neural tissues may be missed in traditional loss-of-function screens. In an effort to circumvent this limitation, we used neuron-specific RNAi knock down in Drosophila and assayed the formation, growth, and maintenance of the neuromuscular junction (NMJ). We examined 1970 Drosophila genes, each of which has a conserved ortholog in mammalian genomes. Knock down of 158 genes in post-mitotic neurons led to abnormalities in the neuromuscular system, including misapposition of active zone components opposite postsynaptic glutamate receptors, synaptic terminal overgrowth and undergrowth, abnormal accumulation of synaptic material within the axon, and retraction of synaptic terminals from their postsynaptic targets. Bioinformatics analysis demonstrates that genes with overlapping annotated function are enriched within the hits for each phenotype, suggesting that the shared biological function is important for that aspect of synaptic development. For example, genes for proteasome subunits and mitotic spindle organizers are enriched among the genes whose knock down leads to defects in synaptic apposition and NMJ stability. Such genes play essential roles in all cells, however the use of tissue- and temporally-restricted RNAi indicates that the proteasome and mitotic spindle organizers participate in discrete aspects of synaptic development. In addition to identifying functional classes of genes shaping synaptic development, this screen also identifies candidate genes whose role at the synapse can be validated by traditional loss-of-function analysis. We present one such example, the dynein-interacting protein NudE, and demonstrate that it is required for proper axonal transport and synaptic maintenance. Thus, this screen has identified both functional classes of genes as well as individual candidate genes that are critical for synaptic development and will be a useful resource for subsequent mechanistic analysis of synapse formation and maintenance
Drosophila Rae1 controls the abundance of the ubiquitin ligase Highwire in post-mitotic neurons
No full textLoss of the spectraplakin short stop activates the DLK injury response pathway in drosophila
No full textSkpA restrains synaptic terminal growth during development and promotes axonal degeneration following injury
No full textThe Wallenda (Wnd)/dual leucine zipper kinase (DLK)-Jnk pathway is an evolutionarily conserved MAPK signaling pathway that functions during neuronal development and following axonal injury. Improper pathway activation causes defects in axonal guidance and synaptic growth, whereas loss-of-function mutations in pathway components impairs axonal regeneration and degeneration after injury. Regulation of this pathway is in part through the E3 ubiquitin ligase Highwire (Hiw), which targets Wnd/DLK for degradation to limit MAPK signaling. To explore mechanisms controlling Wnd/DLK signaling, we performed a large-scale genetic screen in Drosophila to identify negative regulators of the pathway. Here we describe the identification and characterization of SkpA, a core component of SCF E3 ubiquitin ligases. Mutants in SkpA display synaptic overgrowth and an increase in Jnk signaling, similar to hiw mutants. The combination of hypomorphic alleles of SkpA and hiw leads to enhanced synaptic growth. Mutants in the Wnd-Jnk pathway suppress the overgrowth of SkpA mutants demonstrating that the synaptic overgrowth is due to increased Jnk signaling. These findings support the model that SkpA and the E3 ligase Hiw function as part of an SCF-like complex that attenuates Wnd/DLK signaling. In addition, SkpA, like Hiw, is required for synaptic and axonal responses to injury. Synapses in SkpA mutants are more stable following genetic or traumatic axonal injury, and axon loss is delayed in SkpA mutants after nerve crush. As in highwire mutants, this axonal protection requires Nmnat. Hence, SkpA is a novel negative regulator of the Wnd-Jnk pathway that functions with Hiw to regulate both synaptic development and axonal maintenance
