MSc Exit Seminar - Daniel Johnson (Goring Lab)
MSc Exit Seminar
Wednesday July 13th, 1:10 pm – Earth Sciences Centre, Rm. 3087
Daniel Johnson (Goring lab)
"Trafficking Dynamics in Arabidopsis Pollen-Stigma Interactions"
Abstract
Reproduction in the Brassicaceae family depends on self-recognition, where cross-compatible pollen is distinguished from self-incompatible pollen prior to acceptance by the stigma. The stigma only gives compatible pollen the resources required for hydration and germination of a pollen tube for fertilization. These resources are sequestered away from self-incompatible pollen, inhibiting inbreeding. Many questions remain surrounding the specific signalling events that govern this self-recognition system. This research investigates how resource delivery to self-incompatible pollen is prevented in Arabidopsis. Topics explored include the localization of Sec5a, an exocyst complex member that delivers secretory vesicles to compatible pollen; the localization of ARC1, an E3 ubiquitin ligase which prevents the exocyst from delivering resources; and autophagy’s degradation of the sequestered resources.
MSc Exit Seminar - Téa Pavlović - (D. Lovejoy lab)
MSc Exit Seminar
Thursday July 7th, 10:10 am - Ramsay Wright Building, Rm. 432
Téa Pavlović (Lovejoy lab)
"A novel route for steroidogenesis via the teneurins and adhesion GPCR signaling: the emerging role of teneurin C-terminal associated peptide in mammalian reproduction"
Abstract
Teneurin C-terminal associated peptide (TCAP) is a peptide sequence encoded by the terminal exon of each of the four teneurin genes and has a structural similarity to corticotropin releasing hormone (CRH) and peptides associated with the secretin family. It binds and activates the ADGRL1 receptor (latrophilin), a G-protein coupled receptor (GPCR) with structural similarities to the CRH and secretin family of GPCRs. Moreover, TCAP and teneurins associate with dystroglycan transmembrane proteins along with ADGRL1. Together, these players form an intercellular adhesion complex capable of activating PLC-PKC cell signalling cascades, respectively. Previous studies in mice have shown that TCAP-1 is highly expressed in the mouse testes and epididymis. In vivo data indicate that TCAP-1 can increase both serum and fecal testosterone concentrations. New studies using immortalized Leydig (TM3) and Sertoli (TM4) cells suggest that TCAP-1 activates these cells differentially. In TM3 cells, a significant increase in testosterone synthesis was observed upon TCAP-1 stimulation, indicating that this mechanism may be independent of GnRH and gonadotropin action. New evidence now indicates that this mechanism may in fact be dependent upon binding and activation of the ADGRL1 adhesion receptor. These data together have uncovered a potentially new peptide member that plays a role in the regulation of reproduction in the mammalian testes.
Ramsay Wright is a wheelchair accessible building.
MSc Exit Seminar - Iram Sobia Khan (Terebiznik lab)
MSc Exit Seminar
Monday June 27th, 2:10 pm - Room MW 229, University of Toronto at Scarborough
Iram Sobia Khan (Terebiznik lab)
"Biogenesis and Maturation of Asbestos-containing Phagosomes in Macrophages"
Abstract
Exposure to asbestos has been associated with many pathogenic effects, including the development of malignant mesothelioma and bronchogenic carcinoma. Fibres are inhaled and circumvent the ciliated airways, depositing in areas of the lungs such as the alveoli and pleura where they become targets for removal via phagocytosis. The field of fibre toxicology has proposed a model, termed the fibre pathogenicity structure: activity paradigm, to explain the pathogenicity of asbestos and other respirable fibres. This model identifies length as being critical to toxicity and states that fibres exceeding 15 μm are problematic for removal by macrophages, purportedly causing frustrated phagocytosis. This pro-inflammatory condition stimulates cells to release inflammatory mediators and damaging reactive oxygen species, contributing to fibrosis and tissue damage. Although frustrated phagocytosis is widely accepted as being an explanation for asbestos-induced toxicity, the cellular mechanisms involved in this process are not well understood. To study the mechanisms involved in this phenomenon, we followed the phagocytosis of asbestos fibres in cultured and primary human and murine macrophages.
Our results demonstrate that the fibre length internalized by macrophages easily surpasses the threshold length proposed by the paradigm, and that the time required for uptake is length-dependent. Following phagosome formation, maturation progresses to different stages based on the cell type, with maturation stalling at early stages in human and primary murine cells. In contrast, the maturation of asbestos-containing phagosomes proceeds in RAW 264.7 cultured murine macrophages, as evidenced by the fusion of endosomes with these compartments and the subsequent acquisition of characteristics of a maturing phagosome. In all cells, however, phagosomes containing asbestos fail to acidify, suggesting a defect in phagosomal maturation that may contribute to fibre pathogenicity.
Altogether, our results indicate that fibre length is not the primary factor in asbestos-induced toxicity and suggest that surface chemistry may contribute to a greater extent to the development of asbestos-related diseases.
MSc Exit Seminar - Eshan Naik (Campbell lab)
MSc Exit Seminar
Tuesday June 14th, 10:10 am - Room SW 403, University of Toronto at Scarborough
Eshan Naik (Campbell lab)
"A chemical genetics approach to explore anthocyanin regulation in nitrogen-deprived Arabidopsis seedlings"
Abstract
Plants often experience varying soil nitrogen levels during their life cycle, and adjust growth and development to accommodate these changes. A typical plant response to limiting nitrogen involves an increase in the production of anthocyanins. As such biochemical alterations have a profound impact on plant survival, there is interest in better understanding the molecular determinants that underpin these responses. In the present study, a chemical genetics approach was implemented to discover molecular components involved in the induction of anthocyanin biosynthesis, in response to altered nitrogen levels. Using a robust high-throughput screening method, a chemical library was screened to discover compounds capable of attenuating anthocyanin levels in nitrogen-deprived Arabidopsis seedlings. Chemical screens were successful in identifying four compounds that appear to mis-regulate the accumulation of anthocyanins during nitrogen deprivation. The impact of the compounds on the low-nitrogen response was characterized, and the results indicate that chemical application must occur at a specific developmental stage. Furthermore, low nitrogen-induction of anthocyanins is highly sensitive to chemical application, and chemicals appear to exert their effect throughout early seedling growth. While structure-activity relationships have been examined, mutational and genome-wide studies will bridge the gap in understanding the attenuation of the link between anthocyanin biosynthesis and nitrogen availability.
MSc Exit Seminar - Reem Merwass (AbouHaidar lab)
MSc Exit Seminar
Thursday May 12th, 1:10 pm – Earth Sciences Centre, Rm. 3087
Reem Merwass (AbouHaidar lab)
"Requirement(s) for the Replication of Lucerne Transient Streak Virus Satellite RNA"
Abstract
The satellite RNA of Lucerne Transient Streak Virus (LTSV) is a 322-nucleotide, single-stranded circular RNA with a high degree of base-pairing (70%) that has a rod-like structure very similar to that of viroids. As it does not encode any translation products and cannot replicate independently of a helper virus, the satellite RNA is proposed to rely on viral-encoded proteins for the replication and cell-to-cell movement that facilitate its systemic infection in a host. To investigate the requirements for replication and cell-to-cell movement of the LTSV satellite RNA, transgenic plant systems were generated to express the viral RNA-dependent RNA polymerase. Results of infectivity assays of these transgenic lines demonstrated for the first time that the viral encoded RNA-dependent RNA polymerase is necessary and sufficient for the replication of LTSV satellite RNA, and no additional viral-encoded protein products for its cell-to cell or systemic transport are needed. Since some studies of cell-to-cell movement in plants indicate that plasmodesmata have a molecular size exclusion limit between 700 and 800 daltons, the LTSV satellite RNA (with a molecular size of approximately 109 kDa) may be able to interact with plasmodesmata in such a way as to allow for its movement without the assistance of other viral or host-encoded proteins.
MSc Exit Seminar - Ruben Flam-Shepherd (Kronzucker lab)
MSc Exit Seminar
Wednesday March 2nd, 4:10 pm - Ramsay Wright Building, Rm. 432 (rescheduled)
Ruben Flam-Shepherd (Kronzucker lab)
"An Examination of the Role of Silicate in Sodium Transport and Salinity Tolerance in Rice (Oryza sativa)"
Abstract
Silicate (Si)-mediated alleviation of salinity toxicity in rice is proposed to be exerted through a decrease in apoplastic sodium (Na+) transport. This is said to decrease shoot Na+ accumulation, a commonly proposed salt tolerance strategy. To investigate this, salt tolerant (Pokkali) and salt sensitive (IR29) rice cultivars were grown in either 0 or 1.67 mM Si over a range of Na+ concentrations, and cultivar-specific effective concentrations of Na+ at which shoot fresh weight was decreased by 50% were determined. Within this experimental framework, salinity tolerance strategies were characterized using the radiotracer 24Na+ in conjunction with electrophysiological, photometric, and fluorescent dye measurements. Si treatment was found to decrease shoot Na+ accumulation by over 50% in both cultivars, while having no effect on transmembrane ion currents. Si-treated IR29 exhibited lowered apoplastic bypass and shoot Na+ flux, though no effect was seen in Pokkali. Examinations of Na+ efflux and shoot-to-root recirculation in Pokkali were unable to reconcile differences between shoot Na+ content and tracer-flux analyses.
Ramsay Wright is a wheelchair accessible building.
MSc Exit Seminar - Gregory Martyn (Vanlerberghe lab)
MSc Exit Seminar
Thursday February 4th, 10:10 am – Room SW403, University of Toronto at Scarborough
Gregory Martyn (Vanlerberghe lab)
"The Impact of Alternative Oxidase on Nitrogen Stress in Nicotiana tabacum"
Abstract
Nitrogen applied in limiting quantities (low nitrate) or as an unfavourable source (ammonium) disrupts the fine-tuned rates of turnover of the adenylate and pyridine nucleotide pools in plants leading to stress. The alternative oxidase (AOX) is an abiotic stress response protein that relaxes the tight coupling between NAD(P)H oxidation and ATP synthesis, thus restoring cellular energy homeostasis. To investigate whether AOX has an impact on these “nitrogen stress” scenarios, wild-type Nicotiana tabacum were compared to AOX knockdown and overexpression lines grown in either nitrate or ammonium at 100µm, 1mM, 5mM concentrations as well as under 16 day nitrogen deprivation and 10mM ammonium. Using gas exchange and chlorophyll a fluorescence in addition to qRT-PCR and western blotting we demonstrate that AOX was imposing photosystem stoichiometry adjustments in plants grown at 100 µM nitrate. Under severe nitrogen deprivation, mitochondrial respiration in the dark (RD) and light (RL) were consistent with improved photosynthetic capacity and AOX overexpression. All plants grown under 10mM ammonium displayed symptoms of ammonium toxicity. AOX expression under ammonium toxicity was significantly positively correlated with photosynthetic capacity in later parts of the day. These results demonstrate that AOX is an important component of the nitrogen stress response in plants and could even be beneficial under extreme nitrogen stress conditions.
MSc Exit Seminar - Bianca Scuric (Ringuette lab)
MSc Exit Seminar
Monday January 18th, 10:10 am - Ramsay Wright Building, Rm. 432
Bianca Scuric (Ringuette lab)
" Role of SPARC in Drosophila melanogaster basal lamina homeostasis"
Abstract
SPARC is a multifunctional, evolutionarily conserved, collagen- and growth factor-binding glycoprotein. Previous studies in our laboratory demonstrated that SPARC is required in Drosophila melanogaster for proper larval development and maintenance of fat body homoeostasis. Through the use of RNA interference, I have further characterized a SPARC knockdown in the larval fat body, with an emphasis on ultrastructural adipocyte morphology and basal lamina integrity. Loss‐of‐function analyses revealed remodeling of adipocytes characterized by cell rounding and dense accumulation of fibrous matrix material beneath a basal lamina of abnormal thickness. In addition to dramatic changes in cell morphology, adipocytes of SPARC deficient larva show increased deposition of collagen IV and other basal lamina components (Martinek et al., 2011; Shahab et al., 2015). How collagen IV assembles into an organized network in basal lamina remains unclear. I sought to elucidate the potential intra- and extracellular functions of SPARC in collagen IV assembly and maturation within the basal lamina surrounding larval adipocytes. To perform in vivo structure function analysis, I generated five mCherry tagged SPARC constructs which failed to rescue loss-of-function and SPARC-null mutants. Although fluorescence was observed in all transgenic animals, stability of the SPARC protein was comprised by the C-terminal tag. Together, the data compiled by myself and others in the lab indicate that SPARC is required to maintain adipocyte morphology and basal lamina homeostasis during larval development.
Ramsay Wright is a wheelchair accessible building.
MSc Exit Seminar - Nouf Alluqmani (Treanor lab)
MSc Exit Seminar
Tuesday January 12th, 2:10 pm - Room MW 229, University of Toronto at Scarborough
Nouf Alluqmani (Treanor lab)
"Galectin-9 regulates B cell receptor signaling"
Abstract
B cells are an essential component of the adaptive immune system, which secrete soluble antibody against pathogen (antigen). B cells recognize antigen through the B cell receptor (BCR), which triggers receptor clustering and intracellular signaling. Despite this key feature of B cell activation, the mechanisms that cluster antigen receptors are not well understood. Given that glycan-galectin lattices have been shown to regulate cell surface glycoprotein organization and signaling, it seems likely that these cell surface structures may regulate receptor clustering in B cells. One of these potential galectins regulating B cell signaling is Galectin-9 (Gal-9); a secreted lectin with two carbohydrate recognition domains linked by a flexible peptide. A recent report found that antibody production is increased in Gal-9 deficient mice; however the molecular mechanism for this observation has not been investigated. Here, we show that Gal-9 is expressed at the cell surface of primary naïve B cells, organized into discrete puncta. Given the potential of Gal-9 to regulate protein-protein interactions at the cell membrane, we examined the effect of Gal-9 deficiency on the formation of BCR signaling microclusters. Using artificial planar lipid bilayers to mimic membrane-bound antigen, we found that deficiency in Gal-9 leads to enhanced BCR microcluster formation and increased proximal BCR signaling. This increased signaling in Gal-9 deficient B cells can be attenuated by treatment with exogenous Gal-9. Moreover, treatment of wild-type naïve B cells with exogenous Gal-9 is sufficient to nearly completely inhibit cell signaling upon BCR stimulation, suggesting that Gal-9 acts as a negative regulator of B cell activation. Using a pull-down assay and mass spectrometry, we identified CD45 and IgM as ligands for Gal-9. We show that treatment with exogenous Gal-9 induced relocalization of IgM and CD45 to Gal-9 lattices. Taken together, our data suggests that Gal-9-glycoprotein interactions at the surface of B cells play an important role in regulating B cell signaling and consequently B cell activation.
MSc Exit Seminar - Ashpreet Saini (Levine lab)
MSc Exit Seminar
Monday January 11th, 9:30 am - Room HSC 330, University of Toronto at Mississauga
Ashpreet Saini (Levine lab)
"Characterizing Genes Associated with Social Interactions in Drosophila melanogaster"
Abstract
Social behaviour is seen among a variety of organisms. Drosophila melanogaster engages in many social behaviours including courtship and mating. The fly has also exhibited the ability to alter the rhythmic timing of its behaviours based on the social composition of the group. The rhythmic timing of behaviours in Drosophila is regulated by the endogenous biological clock. There are many crucial components of the circadian clock, which work together to help regulate behavioural rhythms. Some of these components, such as clock genes, can thereby be used to examine the status of the clock. The aim of this work is to characterize the role that the CG42343 locus plays in directing social interactions. We demonstrate that the CG42343 locus plays a role in regulating social interactions through changes in expression levels of clock genes, and that this phenomenon is likely mediated through chemosensory signaling.