MSc Exit Seminar - Rosemary Saati (Fulthorpe lab)
MSc Exit Seminar
Friday September 16th, 11:10 am – Room SW 403, University of Toronto at Scarborough
Rosemary Saati (Fulthorpe lab)
"Characterization of the Cyanobacterial Harmful Algal Bloom Community in Hamilton Harbour, Lake Ontario"
Abstract
Despite management efforts to decrease exogenous phosphorus loadings since the 1970’s into Hamilton Harbour, the bay has seen a reappearance of Cyanobacterial harmful algal blooms (CyanoHABs) often dominated by the notorious colonial toxin producer Microcystis and other filamentous bloom-forming genera. Studies on CyanoHAB communities in freshwater systems have concentrated on Cyanobacterial species composition and the physico-chemical factors influencing their growth in culture experiments. Little is known about the interspecific relationships between Cyanobacteria, heterotrophic species and the impact on natural grazer dynamics mainly since most aquatic species are non-culturable in the laboratory. Culture-independent methods have recently revealed that heterotrophs are abundant and diverse in freshwater although their interactions with Cyanobacteria throughout blooms remain unknown. I applied these methods to elucidate the epilimnetic community composition throughout the summers of 2014 and 2015. Correlations were determined between community structure determined by Terminal Restriction Length Polymorphism (T-RFLP) of community 16S and 18S rRNA genes to the physico-chemical parameters collected on site. The most influential factors on community structure in 2014 were chloride and sulfate concentration whereas nitrate/nitrite and ammonium had a stronger influence on the 2015 community. Community composition associated with these blooms was investigated using 454-pyrosequencing and shotgun metagenomics. Taxonomy assignment revealed a predominance of Actinobacteria and Proteobacteria in June/July samples. The Actinobacteria:Cyanobacteria ratio decreased both summers with Planctomycetes emerging during Cyanobacteria predominance in August/September. Analysis of eukaryotic ribosomal genes revealed a diversity of Metazoa, Chlorophyta, and SAR group including a novel Rhizaria in 2014 but shotgun data from the 2015 samples suggested eukaryotes encompassed a significantly smaller of the total community compared to bacteria. Nitrate/nitrite uptake and intracellular reduction by Cyanobacteria and Betaproteobacteria as well as Cyanobacterial nitrogen fixation genes increased throughout the summer suggesting that microorganisms that could take advantage of ammonium limitation in August and September predominated. These results provide the first characterization of the overall CyanoHAB community in Hamilton Harbour as well as a reference point for future studies on this system and other similar systems. They further provide new insights for future management into which environmental factors are likely shaping this specific community throughout the summer.
MSc Exit Seminar - Amy Zhang (Guttman/Desveaux Labs)
MSc Exit Seminar
Friday September 16th, 10:10 am - Ramsay Wright Building, Rm. 432
Amy Zhang (Guttman/Desveaux labs)
"Preliminary mapping of HopZ1b resistance-associated loci in Arabidopsis thaliana via EMS and ecotype screens"
Abstract
Pseudomonas syringae is a global plant pathogen that infects agriculturally important crops and the model organism Arabidopsis thaliana. P. syringae deploys type III secreted effectors to suppress immunity and enhance bacterial growth. However, plants possess resistance proteins to recognize these effectors. Thus, effectors have diversified over time to evade recognition. For example, in Arabidopsis Columbia-0, HopZ1a effector triggers robust immunity through ZAR1 resistance protein, but the related HopZ1b elicits a weak resistance-like phenotype.
We conducted EMS and ecotype forward genetic screens to identify induced and natural variations conferring HopZ1b resistance. We found one EMS mutant and one ecotype Gabelstein-0 with enhanced resistance to HopZ1b. Resistance was correlated with bacterial growth inhibition, and enhanced by surface inoculation of bacteria rather than direct injection into plant tissue. Resistance was also dependent on putative effector catalytic function and localization. Preliminary analysis of Gabelstein-0 ZAR1 sequence found an enrichment of variations in the NB-ARC domain. NB-ARC domain acts as a molecular switch for resistance protein activation, and variations in this domain may facilitate activation to the weakly recognized HopZ1b effector.
Ramsay Wright is a wheelchair accessible building.
MSc Exit Seminar - Priscilla Tang (Varmuza lab)
MSc Exit Seminar
Friday September 16th, 12:30 pm – Earth Sciences Centre, Rm. 3087
Priscilla Tang (Varmuza lab)
"SFMBT2 Function in Chromatin Architecture Mediates Trophoblast Stem Cell Maintenance"
Abstract
The mammalian Polycomb Group (PcG) gene Sfmbt2 is implicated in embryonic viability specifically through the maintenance of the trophoblast stem (TS) cells and their contribution to development of the placenta. Despite its critical role in placental development, mechanisms underlying SFMBT2 function are still unknown. To elucidate the regulatory role SFMBT2 plays in TS cell maintenance, I performed ChIP-seq analyses against endogenous and FLAG-SFMBT2. Additionally, I analyzed the transcriptomes of Sfmbt2-null embryos using RNA-seq. Consistent with its classification as a PcG protein, 75% of differentially expressed genes were upregulated in the e7.5 extraembryonic tissues of SFMBT2-null murine embryos. Genome-wide SFMBT2 localization analyses revealed broad binding profiles suggesting SFMBT2 recruitment is more complex than its Drosophila counterpart dSfmbt. Further analysis of called SFMBT2 peaks revealed preferential localization to repetitive elements, specifically LINEs and major satellite sequences, and lncRNAs. Lastly, a consistent pattern of histone and transcription factor accumulation across SFMBT2 peaks was observed. Collectively, the data suggest that SFMBT2 plays a complex regulatory role in mediating chromatin architecture which may contribute to the maintenance of stemness in TS cells.
MSc Exit Seminar - Nakisa Malek-Gilani (Mitchell lab)
MSc Exit Seminar
Wednesday September 14th, 10:10 am - Ramsay Wright Building, Rm. 432
Nakisa Malek-Gilani (Mitchell lab)
"The Importance of Cell Specific Transcription Factors in Sox2 Regulation, Conservation and Reprogramming"
Abstract
The Sox2 gene codes for a HMG box transcription factor that is critical for the self-renewal and pluripotency of embryonic stem (ES) cells. Although Sox2 is expressed in ES cells the cell-type specific regulation of Sox2 transcription is only just being investigated; with a distal Sox2 Control Region (SCR) recently being discovered. The aim of this study was to expand on the knowledge of SCR enhancer activity, specifically the role of cell specific transcription factor binding in the region. The main finding of this study was two clusters of ES cell specific transcription factor binding motifs conferring enhancer activity to active regions within the SCR. Using these motifs studied in mice, a putative functionally conserved SCR region in human was located. This putative human Sox2 control region (hSCR) demonstrates high sequence conservation of ES cell specific TF motifs and two distinct clusters as seen in mouse. Overall, these results suggest TF binding at Sox2 distal enhancers is vital for activity and could be conserved across species.
Ramsay Wright is a wheelchair accessible building.
MSc Exit Seminar - Wenjing Xia (Anderson/Kohn labs)
MSc Exit Seminar
Monday September 12th, 10:10 am – Room IB 200, University of Toronto at Mississauga
Wenjing Xia (Anderson/Kohn labs)
"Micro-Scale Diversity and Persistence of Genomic Variants of the Yeast Saccharomyces Paradoxus in a Natural Woodland Population"
Abstract
Alcohol Genetic diversity in experimental, domesticated, and wild populations of the related yeasts, Saccharomyces cerevisiae and S. paradoxus, has been well described at the global scale, but rarely on a small spatial scale. While large-scale sampling is informative on the roles of biogeography in shaping population structure, fine scale sampling over time captures stability and flux in genome distribution and interaction, which may not be revealed in large-scaled studies. In this thesis, I investigated the population genomics of a local population on a fine spatial scale to address two main questions. First, is there genomic variation in a S. paradoxus population at a spatial scale spanning centimeters (microsites) around individual trees to tens of meters? Second, does the distribution of genomic variants persist over time? My sample consisted of 42 S. paradoxus strains from 2014 and 43 strains from 2015 collected from the same 72 microsites around four host trees (Quercus rubra and Q. alba) within 1km2 in a mixed hardwood forest in southern Ontario. Six additional S. paradoxus strains recovered from adjacent maple and beech trees in 2015 are also included in the sample. Whole-genome Illumina sequencing and genomic SNP analysis revealed five differentiated groups (clades) within the sampled area. The signal of persistence of genotypes in their microsites from 2014 to 2015 was highly significant. Isolates from the same tree tended to be more related than strains from different trees, with limited evidence of dispersal between trees. The results indicate that different clades co-exist at fine spatial scale and that population structure persists over time in these wild yeasts.
MSc Exit Seminar - Mia Husić (Lovejoy lab)
MSc Exit Seminar
Friday September 9th, 11:30 am - Ramsay Wright Building, Rm. 432
Mia Husić (Lovejoy lab)
"Binding, activation and cellular actions of teneurin C-terminal associated peptide (TCAP)-1 with its putative receptor, latrophilin-1 (ADGRL1), in immortalized cell lines"
Abstract
The teneurins are multifunctional type-II transmembrane proteins that bind the adhesion G-protein coupled receptor subfamily L/latrophilin (ADGRL) in the only intermolecular synaptic adhesion unit conserved between invertebrates and vertebrates. However, the specific interaction between teneurin and ADGRL is not well understood. The distal extracellular region of teneurin possesses a potentially cleavable bioactive peptide termed the ‘teneurin C-terminal associated peptide’ (TCAP). A synthetic version of TCAP-1 is highly active in cells, causing increased expression of cytoskeletal components and actin re-arrangement. Yet the mechanism by which TCAP-1 induces these effects remains unclear. HCT116 cells over-expressing ADGRL1 have increased uptake of TCAP-1 compared to wild-type cells. ADGRL1 expression causes increased adhesion between cells and reduces their expression of f-actin. TCAP-1 treatment induces f-actin polymerization and modulation of cellular morphology only in ADGRL1-expressing cells. These data are the first to establish TCAP-1 as an endogenous ADGRL1 ligand, and further elucidate its mode of action.
Ramsay Wright is a wheelchair accessible building.
MSc Exit Seminar - Victoria Yan (Tepass lab)
MSc Exit Seminar
Tuesday September 6th, 3:10 pm - Ramsay Wright Building, Rm. 432
Victoria Yan (Tepass lab)
"Drosophila α-Catenin regulates growth and EMT"
Abstract
α-catenin (Drosophila α-Catenin/α-Cat) is a linker between the cadherin-catenin complex and the actomyosin cytoskeleton at adherens junctions (AJs) in epithelial cells. The mammalian homologue αE-catenin is a tumour suppressor. Previous studies in mouse knockout skin cells showed a growth suppressive role for αE-catenin, although the underlying molecular mechanism is poorly defined. Whether α-catenin is involved in growth regulation at the AJs or as a cytoplasmic factor remains unclear. α-Cat is mechanosensitive and can undergo a conformational change upon actomyosin contractions to recruit α-Cat binding partners. The function of α-Cat’s mechanosensing is currently not understood. I investigated the role of Drosophila α-Cat in proliferation, and whether α-Cat acts as a mechanosensor at the AJs to regulate Hippo signaling. Using mosaic analysis and tissue-wide RNAi knockdown (KD) in the Drosophila wing disc epithelium, I showed that α-Cat has a dosage-dependent effect on epithelial integrity, proliferation and cell survival, which has allowed us to uncouple α-Cat’s functions in growth regulation and adhesion. α-Cat null cells undergo epithelial to mesenchymal transition (EMT). Intermediate loss of α-Cat resulted in both autonomous and non-autonomous overgrowth. Cells depleted of α-Cat KD activate JNK signaling and upregulate Yorkie activity. Proliferation of WT cells adjacent to α-Cat KD cells is also enhanced through non-autonomous upregulation of Yorkie activity. To determine whether α-Cat regulates growth at the AJs, I tested the effects of DE-cadherin KD, and identified dosage-dependent defects similar to that of α-Cat RNAi KD, which suggests that α-Cat and DE-cadherin regulate proliferation together at the AJs. Additionally, α-Cat fused to DE-cadherin can rescue proliferation defects in α-Cat KD cells, indicating that a pool of cytosolic α-Cat is not required in growth regulation. Moreover, I showed that the mechanosensitive middle region of α-Cat is dispensable for α-Cat’s function in adhesion and proliferation control. My work identified a novel role for α-Cat as a growth regulator at the AJs, in addition to adhesion. This work will stimulate future investigations into how the α-Cat-centered protein network contributes to growth regulation in normal development as well as cancer progression.
Ramsay Wright is a wheelchair accessible building.
MSc Exit Seminar - Jonah Chevrier (Woodin lab)
MSc Exit Seminar
Tuesday August 16th, 2:10 pm - Ramsay Wright Building, Rm. 432
Jonah Chevrier (Woodin lab)
"Cation chloride cotransporters exist with NMDA receptors in molecular complexes"
Abstract
In the central nervous system, the polarity of GABAergic synaptic transmission is predominantly determined by cation-chloride cotransporters NKCC1 and KCC2. During development, functional expression of chloride-loading NKCC1 decreases while chloride-extruding KCC2 is steeply upregulated and underlies the GABA switch from excitatory to inhibitory. Despite the critical role of KCC2 in inhibitory neurotransmission, excitatory kainate-type glutamate receptor subunit GluK2 interacts with and regulates KCC2 function. The aim of this study was to determine if N-methyl-D-aspartate receptors (NMDARs) interact with NKCC1 and KCC2. The salient findings of my work are: (i) NKCC1 and KCC2 interact with NMDARs in neurons throughout development and into maturity (ii) loss of NMDARs alters expression of KCC2 and (iii) traumatic brain injury alters cation-chloride cotransporter expression and interactions with NMDARs. This work contributes to our knowledge of the molecular interplay between the opposing forces of neuronal excitation and inhibition.
Ramsay Wright is a wheelchair accessible building.
MSc Exit Seminar - Sadek Shorbagi (Brown lab)
MSc Exit Seminar
Tuesday August 2nd, 2:10 pm - Room SW 403, University of Toronto at Scarborough
Sadek Shorbagi (Brown lab)
"Dynamics of the association of heat shock protein HSPA6 (Hsp70B') and HSPA1A (Hsp70-1) with stress-sensitive cytoplasmic and nuclear structures in differentiated human neuronal cells"
Abstract
Heat shock proteins (Hsps) are cellular repair agents that counter the effects of protein misfolding that is a characteristic feature of neurodegenerative diseases. HSPA1A (Hsp70-1) is a widely studied member of the HSPA (Hsp70) family. The little studied HSPA6 (Hsp70B') is present in the human genome and absent in mouse and rat, hence it is missing in current animal models of neurodegenerative diseases. Differentiated human neuronal SH-SY5Y cells were employed to compare the dynamics of the association of YFP-tagged HSPA6 and HSPA1A with stress-sensitive cytoplasmic and nuclear structures. Following thermal stress, live imaging confocal microscopy and Fluorescence Recovery After Photobleaching (FRAP) demonstrated that HSPA6 displayed a prolonged and more dynamic association, compared to HSPA1A, with centrioles that play critical roles in neuronal polarity and migration. HSPA6 and HSPA1A also targeted nuclear speckles, rich in RNA splicing factors, and the granular component of the nucleolus that is involved in rRNA processing and ribosomal subunit assembly. HSPA6 and HSPA1A displayed similar FRAP kinetics in their interaction with nuclear speckles and the nucleolus. Subsequently during the recovery from neuronal stress, HSPA6, but not HSPA1A, localized with the periphery of nuclear speckles (perispeckles) that have been characterized as transcription sites. The stress-induced association of HSPA6 with perispeckles displayed the greatest dynamism compared to the interaction of HSPA6 or HSPA1A with other stress-sensitive cytoplasmic and nuclear structures. This suggests involvement of HSPA6 in transcriptional recovery of human neurons from cellular stress that is not apparent for HSPA1A.
MSc Exit Seminar - Larissa Becirovic (Brown lab)
MSc Exit Seminar
Thursday July 28th, 10:10 am - Room SW 403, University of Toronto at Scarborough
Larissa Becirovic (Brown lab)
"Localization of Heat Shock Protein HSPA6 (HSP70B') to the Periphery of Nuclear Speckles is Disrupted by a Transcription Inhibitor Following Thermal Stress in Human Neuronal Cells"
Abstract
Heat shock proteins (Hsps) are a set of highly conserved proteins involved in cellular repair and protective mechanisms. The localization of inducible members of the HSPA (HSP70) family can be used as an index to identify stress-sensitive sites in differentiated human neuronal cells. Following thermal stress, the little studied HSPA6 (HSP70B') demonstrated localization to the periphery of nuclear speckles (perispeckles) that are sites of transcription factories, however the widely studied HSPA1A (HSP70-1) did not. The localization of HSPA6 to perispeckles suggests that HSPA6 may be involved in the recovery of transcription in neuronal cells following exposure to thermal stress. Triptolide, a fast-acting transcription inhibitor, knocked down levels of the large subunit of RNA polymerase II, RPB1, during the time-frame when HSPA6 localized to perispeckles following thermal stress. Triptolide was administered to heat shocked human neuronal SH-SY5Y cells stably transfected with YFP-tagged HSPA6. Fluorescent confocal microscopy demonstrated that YFP-HSPA6 did not localize to perispeckles, suggesting the involvement of HSPA6 in transcriptional recovery after thermal stress. Rapid transcriptional recovery of stressed neuronal cells may be beneficial to the human brain that engages in higher cognitive functions compared to mouse and rat. The HSPA6 gene is present in the human genome but not in the genomes of mouse and rat. Hence, current animal models of neurodegenerative diseases lack a potentially protective member of the HSPA family.