MSc Exit Seminar - Matthew Snow (Peever lab)
MSc Exit Seminar
Wednesday December 16th, 10:10 am - Ramsay Wright Building, Rm. 432
Matthew Snow (Peever lab)
"GABA Cells in the Central Nucleus of the Amygdala Control Cataplexy"
Abstract
Cataplexy is a hallmark of narcolepsy characterized by the sudden onset of muscle weakness or paralysis during wakefulness. It can occur spontaneously but is typically triggered by positive emotions like laughter. Although cataplexy was identified over 130 years ago, its neural mechanism remains unclear. Here, we show that a newly identified GABA circuit within the central nucleus of the amygdala (CeA) may play a causal role in promoting cataplexy. We found that, in narcoleptic mice, chemogenetic activation of GABA cells within the CeA triggered a 253% increase in the number of cataplexy attacks without affecting their duration. We also show that GABA cell activation only promotes cataplexy attacks associated with emotionally rewarding stimuli such as wheel running, without impacting spontaneous attacks. Our results indicate that the CeA plays a pivotal role in controlling cataplexy onset, and that emotionally rewarding stimuli may trigger cataplexy by activating GABA cells in the CeA.
Ramsay Wright is a wheelchair accessible building.
MSc Exit Seminar - Christine Nguyen (Stewart lab)
MSc Exit Seminar
Monday November 23rd, 9:30 am – Room DV 3130, University of Toronto at Mississauga
Christine Nguyen (Stewart lab)
"The Influence of Postsynaptic Structures on Missing Quanta at the Drosophila Neuromuscular Junction"
Abstract
Synaptic transmission requires both pre- and post-synaptic elements for neural communication. The postsynaptic structure contributes to the effectiveness of synaptic currents to induce voltage changes in postsynaptic cells. At the Drosophila neuromuscular junction (NMJ), the subsynaptic reticulum (SSR) consists of elaborate membrane folds that link the synaptic contacts to the muscle, but its role in synaptic physiology is poorly understood. In this study, I investigate the function of the SSR by conducting electrophysiological experiments on genetic mutants that up- or down-regulate SSR complexity. I observed that some synaptic currents do not result in postsynaptic voltage changes, events called ‘missing quanta’. Furthermore, the frequency of missing quanta is positively correlated with SSR complexity, observed in both naturally occurring variations of the SSR and in genetic mutants. Based on cable theory, I develop an electrical circuit framework to propose that the SSR contributes to the missing quanta by acting as a filter or a switch for some synaptic events. Further studies directed at understanding the role of the SSR in synaptic transmission and the potential for regulating ‘missing quanta’ will yield important information about synaptic transmission at the Drosophila NMJ.
MSc Exit Seminar - Christine Lum (McGowan lab)
MSc Exit Seminar
Wednesday November 11th, 1:10 pm – Room SW 403, University of Toronto at Scarborough
Christine Lum (McGowan lab)
" Maternal High Fat Diet Alters the Transcriptional Response to Glucocorticoid and Immune Challenge in the Amygdala and Hippocampus of Adult Rat Offspring"
Abstract
Maternal overnutrition during pre- and post-(peri)natal periods of development has previously been suggested to increase offspring risk for developing psychiatric disorders. The mental impacts are often accompanied by altered expressions of glucocorticoid receptors (GR), which regulate the inflammatory response to stress. In this study, rats were acutely injected with corticosterone (CORT) and/or lipopolysaccharide (LPS) in adulthood after perinatal exposure to maternal high-fat diet (HFD) to examine its effects on responding to stress. Gene transcript analyses in the amygdala and hippocampus revealed higher immunosuppressive activity and altered abundance of genes associated with anxiety- and depressive-like behavior over rats perinatally exposed to standard diets. These effects were sex and brain region-specific, and appeared to be dependent on levels of GR. Epigenetic analyses suggest impairments in the DNA methylation machinery to be the cause of these diet differences. Hence, perinatal HFD incurs differential immune responses to stress in the rat brain.
MSc Exit Seminar - Alexander Myrka (Welch lab)
MSc Exit Seminar
Monday November 9th, 10:10 am – Room AA 116, University of Toronto at Scarborough
Alexander Myrka (Welch lab)
"Sweet GLUTs: Quantitative Analysis of Glucose Transporter and Fructolytic Enzyme Transcript Densities in Ruby-Throated Hummingbirds (Archilochus colubris)"
Abstract
Hummingbirds are able to fuel energetically expensive hovering flight entirely with recently ingested glucose or fructose. In other animals, several steps in the pathway of flux of sugars from the gut to muscle are rate-limiting, such as transport into muscle and subsequent phosphorylation. I examined relative expression of facilitative sugar transporters and enzymes of fructolysis in various ruby-throated hummingbird (Archilochus colubris) tissues via quantitative polymerase chain reaction. I hypothesized that the expression of these proteins would be upregulated in hummingbird flight muscle compared to other vertebrates. I found that hummingbird pectoralis displays the highest expression of certain sugar transporter transcripts among vertebrates. I also demonstrated that relative transcript densities of fructolytic enzymes are minimal in hummingbird muscle, suggesting that fructolysis is not a pathway used to rapidly metabolize fructose in these muscles.
MSc Exit Seminar - Saba Haroon (Tepass lab)
MSc Exit Seminar
Tuesday October 6th, 10:10 am - Ramsay Wright Building, Rm. 432
Saba Haroon (Tepass lab)
"Examining the Function of β-catenin at Adherens Junctions during Dorsal Closure and the Formation of the Ventral Epidermis in Drosophila"
Abstract
Adherens junctions (AJs) are made of Cadherin-Catenin Complexes (CCCs); each CCC contains DE-cadherin that binds to p120catenin and β-catenin (Armadillo in Drosophila). Monomeric α-Catenin in turn binds to β-catenin linking the CCC to the actin cytoskeleton. One open question concerning the function of β-catenin is whether it functions only to physically link DE-cadherin to α-Catenin. Alternatively, β-catenin could also act as an important regulator of AJ stability during morphogenetic movements. It has been proposed, for example, that phosphorylation of β-catenin regulates the interaction between β-catenin and its binding partners. Here I have addressed the question whether β-catenin acts only as a physical linker or also has important regulatory functions in Drosophila AJs.
Morphogenetic movements give shape to the developing embryo. One of these morphogenetic movements in Drosophila is dorsal closure. Dorsal closure (DC) is a process by which the dorso-lateral epidermis of an embryo converges to conceal a dorsal opening that is covered by the extra-embryonic amnioserosa. The adhesion between amnioserosa and epidermal cells is regulated to withstand forces during DC while amnioserosa cells contract and are internalized. A second process examined is the formation of the ventral epidermis that undergoes several dynamic movements including cell ingression, cell division, and convergence-extension. DC fails and the ventral epidermis loses integrity when AJs are compromised.
I found that DC defects in embryos lacking DE-cadherin can be partially rescued by fusion proteins that directly link DE-cadherin to α-Catenin without recruiting Armadillo/β-catenin to AJs. This suggests that Armadillo has an important function at AJs for normal DC apart from its role as a linker between DE-cadherin and α-Catenin. In contrast, ventral defects can be completely rescued by a fusion protein of DE-cadherin and α-Catenin that fails to recruit Armadillo, indicating that Armadillo has no essential regulatory function at AJs in this tissue. In addition, in embryos lacking Armadillo, I found that DC defects can be partially rescued by the expression of DE-cadherin α-Catenin fusion proteins. I speculate that the lack of a complete rescue is due to compromised Wnt signalling pathway of which Armadillo is a core component and which has previously been implicated in DC. Together, my results are consistent with the view that Armadillo/β-catenin has a general essential function in linking DE-cadherin to α-Catenin but a tissue-specific regulatory role in controlling AJ dynamics required for morphogenesis.
Ramsay Wright is a wheelchair accessible building.
MSc Exit Seminar - Alexander Fortuna (Yoshioka lab)
MSc Exit Seminar
Tuesday September 29th, 2:30 pm - Earth Sciences Centre, Rm. 3087
Alexander Fortuna (Yoshioka lab)
"Investigating the Interplay of Cyclic Nucleotide Gated Ion Channel 2 and Auxin in Immunity Signaling"
Abstract
Cyclic nucleotide-gated channels (CNGCs) are non-selective, ligand-gated cation channels present across eukaryotes. CNGCs were first identified in animals, where their functions in vertebrate photo-sensory and olfactory neurons are well characterized. Comparably little is known about the physiological roles or biophysical properties of plant CNGCs. In Arabidopsis, the CNGC family contains 20 members, which are believed to play important roles in biotic and abiotic stress responses, ion homeostasis, and development through their Ca2+ conducting abilities. Several CNGCs have been implicated in plant-pathogen interactions through genetic studies. The defense, no death mutants dnd1 and hlm1/dnd2, which are null mutants of the closely related Arabidopsis CNGCs, CNGC2 and CNGC4 have distinct autoimmune phenotypes. This includes elevated levels of salicylic acid, constitutive expression of Pathogenesis Related genes and broad spectrum disease resistance. Though these mutants have been well characterized phenotypically, CNGC-mediated signal transduction is poorly understood.
In order to understand CNGC2-mediated defense signaling, I have investigated the first dnd1 suppressor mutant, repressor of defense no death 1 (rdd1-1D). In this work, I aimed to understand the molecular mechanism by which rdd1-1D is able to suppress dnd1-conferred phenotypes. Current data indicates that rdd1-1D is a loss-of-function mutation in the auxin biosynthesis gene YUCCA6.
MSc Exit Seminar - Ru Yun Chiang (Tropepe lab)
MSc Exit Seminar
Monday September 28th, 10:10 am - Ramsay Wright Building, Rm. 432
Ru Yun Chiang (Tropepe lab)
"The Role of Notch Signaling Pathway during Postembryonic Retinal Neurogenesis in Danio rerio"
Abstract
The retina of teleost fish, such as zebrafish (Danio rerio), exhibits a remarkable capacity for continuous neurogenesis and regeneration throughout life – unlike the mammalian retina. The neurogenic process in the postembryonic zebrafish retina is contributed by two major types of retinal precursor cells: the active stem/progenitor cells in the ciliary/circumferential marginal zone (CMZ) and the Müller glia in the differentiated retina. However, our current understanding of how proliferation and differentiation are regulated in these retinal niches is limited. Notch signaling has been demonstrated to regulate embryonic retinal stem cell behavior in many vertebrate model systems and previous studies have reported the expression of Notch pathway components in the adult zebrafish CMZ. Here I take advantage of the robust neurogenic ability of the zebrafish retina to reveal the expression pattern and functional roles of the Notch signaling pathway during postembryonic retinal development. My research revealed that: (1) Notch signaling is activated predominantly in the differentiated Müller glia; (2) the CMZ cells, despite the expression of Notch receptors, do not exhibit Notch activity and do not require Notch signaling for retinal stem cell maintenance; and (3) Notch signaling is required and sufficient for the proper differentiation of retinal cells in the CMZ, including Müller glia, cone photoreceptor and bipolar cells. These studies demonstrate how different levels of Notch activity regulate retinal stem/progenitor cell behavior and provide insight into how to reactivate/reprogram mammalian adult retinal stem cells in vivo.
Ramsay Wright is a wheelchair accessible building.
MSc Exit Seminar - Catalina Leoveanu (Nambara lab)
MSc Exit Seminar
Wednesday September 23rd, 2:10 pm - Earth Sciences Centre, Rm. 3087
Catalina Leoveanu (Nambara lab)
"The Investigation of Novel Functions of Abscisic Acid 2 Through Protein-Protein Interactions"
Abstract
Abscisic acid (ABA) is a plant hormone that plays a regulatory role in the water stress response, as well as the maintenance of seed dormancy and the mitigation of other abiotic stresses. ABA2 is the enzyme that catalyzes the second-last step in ABA biosynthesis, converting xanthoxin to abscisic aldehyde. The recent discovery of ABA2 nuclear localization and its unique expression pattern may point to a previously uncharacterized function of this enzyme. In order to elucidate novel roles, we analyzed interaction partners using yeast 2 hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays. HAI1, a Protein Phosphatase Type 2 C (PP2C), was found to interact with ABA2, in addition to other members of this family, including ABA-hypersensitive germination 1 (AHG1) and hypersensitive to ABA1 (HAB1). These proteins are members of the core ABA signaling complex and act as negative regulators of ABA-induced gene expression. Preliminary evidence suggests that ABA2 acts through HAI1, and likely other members of the PP2C family, to enhance ABA signaling.
MSc Exit Seminar - Amriya Naufer (Terebiznik lab)
MSc Exit Seminar
Wednesday September 23rd, 1:10 pm - Room MW 229, University of Toronto at Scarborough
Amriya Naufer (Terebiznik lab)
"Phagocytosis of Filamentous Bacteria: Impact of Target Morphology on Phagosomal Maturation"
Abstract
Phagocytosis has primarily been characterized by studies that utilized spheroidal particles as targets. However, phagocytes encounter targets of a disparate morphology in nature. Particles with filamentous morphology can present a hurdle to phagocytosis and yet, our understanding of the cellular mechanisms contributing to this process are limited. For example, during phagocytosis of long filamentous bacterial targets (FT), the nascent phagocytic cups can take more than 30 minutes to be completely internalized. During this time, the phagocytic cup is composed of two distinct domains – the actin-rich domain proximal to the plasma membrane and the internal phagocytic cup, which is embedded within the cytoplasm despite its continuity with the plasma membrane. Interestingly, FT-enclosing phagocytic cups (PCs) can sequentially fuse with endosomes and lysosomes, prior to sealing into a phagosome. Here, we present evidence that PI(3)P, an early endosomal lipid regulator, accumulates significantly at PCs and co-exists with lysosomal protein, LAMP1. Our results indicate that aberrant accumulation of PI(3)P may be a consequence of the neutrality of the compartment on which it is maintained; acidification of phagocytic cups abrogates PI(3)P accumulation at PCs. Remarkably, PI(3)P accumulation was observed to alter significant aspects of the late stage of maturation, primarily evidenced by the delay in late endosomal protein activation. Our findings reveal that key aspects of phagosomal maturation are in fact conditioned by the morphology of the target.
MSc Exit Seminar - Zina Hamoudi (Orchard/Lange labs)
MSc Exit Seminar
Friday September 25th, 1:10 pm - Room CT 2150, University of Toronto at Mississauga
Zina Hamoudi (Orchard/Lange labs)
"Isolation and Characterization of the Corazonin Receptor and Possible Physiological Roles of Corazonin in the Kissing Bug, Rhodnius prolixus"
Abstract
Neuropeptides control many physiological and endocrinological processes in animals, acting as neuroactive chemicals within the central and peripheral nervous systems. Corazonin (CRZ) is one such neuropeptide that has a variety of physiological roles associated with control of heartbeat, ecdysis behaviour initiation, and cuticle colouration. These physiological effects are mediated by the CRZ receptor (CRZR) which is a G protein-coupled receptor. In order to understand the role of the CRZ- signalling pathway in Rhodnius prolixus, the cDNA sequence encoding the RhoprCRZR has been isolated and cloned. The specificity of the RhoprCRZR was examined using CHOK1-aeq cells. Spatial expression pattern using quantitative PCR revealed receptor expression in the central nervous system, dorsal vessel, abdominal dorsal epidermis, and prothoracic glands. Receptor knockdown using dsRNA showed that CRZ maintains a higher heartbeat frequency in intact insects. Preliminary results using the knockdown have yet to show any effect on ecdysis or cuticle colouration.