PhD Transfer Exam - Yunyun Huang (Winklbauer lab)
PhD Transfer Exam
Monday May 9th, 2:10 pm – Ramsay Wright Building, Rm. RW 432
Yunyun Huang (Winklbauer lab)
"Characterizing the Roles of Prickle and Dishevelled in Regulating Cell Adhesion Processes during Xenopus Gastrulation"
Abstract
In Xenopus embryos, mesodermal cells undergo radial intercalation and migrate along the inner surface of the blastocoel roof while remaining separate from the ectoderm. These gastrulation movements require continuous cell-cell adhesion as well as repeated attachment and detachment, the regulation of which has yet to be fully elucidated. Previous work has shown participation of planar cell polarity (PCP) signalling proteins in regulating cell adhesion and separation. Using Prickle1 (Pk1) and Dishevelled2 (Dvl2) as two examples, I will study the role of PCP components in local polarized regulation of cell attachment and detachment during mesodermal cell directional migration. My preliminary data has shown a correlation of Pk1 and Dvl2 with cell detachment behaviour at the rear and lateral sides, respectively. I also found that Pk1 and Dvl2 modulate cell adhesion strength and cortical contractility through up- and downregulation of cortical F‑actin content. My hypothesis is that Pk1 accumulates at the cell trailing edge, and locally up-regulates cortical F-actin to increase contractility of the retraction fibre. I also propose that the diffuse form of Dvl2 promotes lateral cell-cell adhesion by down-regulating cell cortex contractility, whereas Dvl puncta stabilizes distinct lateral adhesion sites between cells. During directional migration, I propose that mesoderm cells are polarized cell-autonomously with respect to Pk1 and Dvl2 puncta localization, and become oriented by ectoderm secreted PDGF-A signalling. Using both in vivo explant systems and in vitro cell spreading assays, I will help clarify how the local, polarized regulation of cell attachment/ detachment contributes to overall cell adhesion and directional migration.
Ramsay Wright is a wheelchair accessible building.
PhD Transfer Exam - Hyun Kyung Lee (Goring lab)
PhD Transfer Exam
Wednesday May 4th, 1:10 pm – Earth Sciences Centre, Rm. ESC 3087
Hyun Kyung Lee (Goring lab)
"Investigating the roles of receptor-like cytoplasmic kinases in Brassicaceae pollen-stigma signalling pathways"
Abstract
Plants have evolved a large number of receptor-like cytoplasmic kinases (RLCKs) that interact with membrane bound receptors to modulate signalling cascades. The focus of my research is on putative RLCKs regulating the initial stages of pollen-stigma interactions in plant reproduction. Once pollen is captured, the stigmatic papillae initiates signalling cascades to deliver water to the pollen grain for hydration and loosen the papillar cell wall for pollen tube entry. However, key signalling components which govern these molecular changes are currently unknown. Simultaneously, in self-incompatible species, the self-incompatibility (SI) pathway can also be activated to circumvent the compatible pollen responses and reject self-pollen. The objective of my PhD thesis is to investigate two putative Arabidopsis thaliana RLCKs pairs, PASK1/2 and APK1a/b, in the compatible and SI signaling pathways, respectively. PASK1/2 are pseudokinases required in the stigma for accepting compatible pollen and may function as scaffolding proteins. In order to elucidate their putative interactors, yeast two-hybrid screening of a flower bud cDNA library was conducted and several potential interactors were identified. To further investigate the specificity of theses interactions, in planta interactions and knockdown and/or knockout lines will be characterized for reduced compatible pollen acceptance. APK1a/b are orthologues of the Brassica SI protein, MLPK, and their role in the A. thaliana SI response is being investigated. Characterization of the SI trait in apk1a/apk1b double knockout lines in the transgenic SI A. thaliana Col-0 lines has given mixed results which may be due to silencing of SI transgenes in the Col-0 ecotype. New A. halleri SI constructs have been cloned and will be tested in the A. thaliana C24 and Sha ecotypes which are known to produce stronger and stable SI phenotypes. SI lines will be generated, and the APK1a/b genes will be silenced using the CRISPR/Cas9 system to induce gene-specific mutations. Overall, this project will provide insight into the roles of two RLCKs pairs in stigmatic papillar signaling pathways regulating the acceptance or rejection of pollen in A. thaliana.
PhD Transfer Exam - Arthur Cheng (Cheng lab)
PhD Transfer Examination
Thursday February 11th, 1:10 pm - DV 3129, University of Toronto at Mississauga
Arthur Cheng (Cheng lab)
" The Role of G Protein Coupled Receptor Kinases in Adult Murine Hippocampal Neurogenesis and Circadian Clock Regulation"
Abstract
G protein-coupled receptors (GPCR) detect a broad spectrum of extracellular signals at the plasma membrane, thereby modulating a wide variety of biological processes. Upon stimulation, GPCRs promote the activation of heterotrimeric G-proteins leading to its dissociation into Gα and Gβγ subunits, both of which modulate different effector systems. Agonist stimulation also triggers complex regulatory mechanisms, so the cellular responses mediated by GPCRs are usually rapidly attenuated, a process termed desensitization. Receptor phosphorylation by specific G protein-coupled receptor kinases (GRKs) plays a key role in triggering rapid desensitization. Phosphorylation of agonist-occupied GPCR by GRKs promotes the binding of cytosolic proteins termed arrestins to the receptor, resulting in the uncoupling and internalization of GPCR from G proteins. Moreover, GRKs may contribute to modulate cellular functions in a phosphorylation-independent manner due to their ability to interact with a variety of proteins involved in signalling and trafficking such as Gαq, Gβγ, clathrin, and caveolin.
The key role that GRKs play in GPCR signalling and modulation suggests that changes in their cellular complement and functionality would strongly affect GPCR function, as has been described in several diseases such as hypertension, congestive heart failure or rheumatoid arthritis. The primary objective of this proposal is to systematically investigate the function of two highly expressed GRKs – GRK2 and GRK5 – in two important biological processes and niches: 1) adult neurogenesis in hippocampal subgranular zone and 2) circadian timekeeping in suprachiasmatic nucleus.
PhD Transfer Exam - Matthew Tran (Richards lab)
PhD Transfer Exam
Thursday February 4th, 12:10 pm - Room 432, Ramsay Wright Building, University of Toronto
Matthew Tran (Richards lab)
"Illuminating the Multisensory Circuit within the Superior Colliculus"
Abstract (Please note there are revisions in text from previous poster)
An often underappreciated capability of the brain is its ability to bind information from different senses to create a vibrant and comprehensive picture of the outside world. Known as multisensory integration (MSI), this ability to combine inputs from multiple sensory modalities is vital for the proper interaction of an organism with its environment. Computational research aimed at understanding the neural calculations required for MSI, has proposed that divisive normalization, mediated by distinct pools of multisensory neurons, can explain many features of MSI. Interestingly, the superior colliculus (SC), a midbrain structure vital for MSI, has been shown to contain a wide variety of cell types with unique morphological, molecular and electrical properties. However, work aimed at understanding how this cellular diversity can account for the computational principles required for MSI, has been extremely limited. The objective of my PhD thesis will be to ascertain whether the SC’s different cellular populations exhibit distinct MSI properties that map onto the functional sub-groups as proposed by the divisive normalization model. Through the use of optogenetics, patch clamp electrophysiology and in vivo two-photon imaging this work could provide a vital link between theoretical computations believed to be critical for multisensory integration and the neurophysiology that underpins them. More fundamentally, by taking this approach to studying neural circuits, we may be able to validate the existence of divisive normalization (a canonical neural computation) in the SC, and thus better understand how the brain uses multisensory information to operate within and encode the world around us.
Ramsay Wright is a wheelchair accessible building.
PhD Transfer Exam - Afif Aqrabawi (Kim lab)
PhD Transfer Exam
Thursday January 28th, 10:10 am - Room 432, Ramsay Wright Building, University of Toronto
Afif Aqrabawi (Kim lab)
"Cortical Control of Olfactory Information Processing: The Role of the Anterior Olfactory Nucleus and Ventral Hippocampus in Vivo"
Abstract
Sensory perception is not simply a feed-forward mechanism. Higher cortical regions actively modulate information processing in lower regions via diverse ‘feedback’ connections. This allows the cortex to suppress or enhance responses in peripheral structures depending on the relevance of the stimuli and to modulate bottom-up information in a manner that matches experience and expectation. In the context of the olfactory system, the role of cortical feedback projections in the awake behaving animal has never been investigated. Using hM4D and hM3D DREADDs, we found that modulating activity of feedback from the anterior olfactory nucleus pars medialis (mAON) in vivo leads to a bidirectional change in olfactory sensitivity and olfaction-dependent behaviours. Furthermore, we demonstrate that optogenetic stimulation of ventral hippocampal terminals at the mAON is sufficient to alter olfaction-dependent behaviours. Future work will focus on how this gain-control function of the mAON plays a role in odour discrimination. Our investigation will also continue to consider the relationship between the hippocampus and the AON and their contribution as top-down modulators of olfactory information processing.
Ramsay Wright is a wheelchair accessible building.
PhD Transfer Exam - Jacob Jezovit (Levine lab)
PhD Transfer Examination
Monday January 25th, 10:10 am - HSC 332, University of Toronto at Mississauga
Jacob Jezovit (Levine lab)
" Investigation and Phylogenetic Characterization of Social Interaction Networks across Multiple Drosophila Species"
Abstract
Formerly known as a solitary organism, Drosophila melanogaster displays a variety of social behaviours, such as aggregation, courtship, aggression and memory/learning. In 2012, a Social Interaction Network (SIN) assay was developed that captured repeatable properties of group organization in flies. A network property, called betweenness centrality, was shown to differ between two strains of D. melanogaster, Canton-S and Oregon-R. An earlier study on social networks in humans also reported betweenness centrality is heritable, emphasizing that these social network models may capture aspects of group organization phenotypes. My project aims to pursue the evolutionary relevance of group organization and social interactions by examining the SINs formed by a collection of diverse Drosophila species. Drosophilids are diverse in their morphology, geographic distribution and ecology and thirty species have had their genomes sequenced. These qualities make Drosophilids a great system to model the evolution of social networks. To date I have characterized SINs in seven species and I found differences in their social networks. I aim to expand this analysis to at least thirteen species and implement comparative phylogenetic methods to model the evolution of SINs in Drosophila. These findings may assist in uncovering genetic correlations to SIN behaviour. More broadly, this work could provide us with a better understanding of genetic, behavioural and evolutionary mechanisms for group organization in social organisms, including humans.
PhD Transfer Exam - Sara Hegazi (Cheng/Levine labs)
PhD Transfer Examination
Thursday December 17th, 11:10 am - DV 3129, University of Toronto at Mississauga
Sara Hegazi (Cheng/Levine labs)
"Elucidating the role of UBR4/POE in the regulation of circadian rhythms in Mus musculus and Drosophila melanogaster"
Abstract
Most organisms possess a widely conserved timekeeping mechanism that is synchronized by daily light:dark cycles to generate 24-hour oscillations in physiology and behaviour. This regulatory mechanism is controlled by a central pacemaker located within the 20,000 neurons of the suprachiasmatic nucleus (SCN) in mammals and within a network of 150 neurons in D. melanogaster.
The central pacemaker achieves circadian regulation through the generation of rhythmic gene expression, where post-translational modifications play a critical role. Post-translational ubiquitination of clock proteins via interactions with ubiquitin ligases marks them for degradation, resetting the clock’s machinery. In a recent mass spectrometry screen, a novel ubiquitin ligase, UBR4, was identified in the murine SCN following light stimulation. Mutant mice for the ubr4 gene exhibit abnormal behavioural rhythms. This suggests that UBR4 is critical for circadian regulation. However, the molecular mechanisms underlying its function remain unknown.
The novelty of UBR4 in circadian timekeeping and its sequence homology across species have prompted the outstanding investigation of its function. I will be carrying out this investigation in two model organisms, M. musculus and D. melanogaster, utilizing the unique advantages offered by each organism for studying circadian timing. I have successfully shown that POE, the fly homolog of UBR4, plays a pivotal role in the generation of behavioural and molecular rhythms. However, the underlying mechanisms are unknown.
My project aims to elucidate the biochemical mechanisms underlying the UBR4/POE-mediated circadian regulation, and to determine whether UBR4/POE is functionally conserved between insects and mammals. Ultimately, my work will establish UBR4/POE as a key regulator in circadian timekeeping, and will potentially permit the extrapolation of our findings to higher organisms such as humans.
PhD Transfer Exam - Serge Parent (Bruce/Winklbauer labs)
PhD Transfer Exam
Friday December 11th, 11:10 am - Room 432, Ramsay Wright Building, University of Toronto
Serge Parent (Winklbauer/Bruce labs)
"Characterization of the initiation and progression of intercellular adhesion between homotypic and heterotypic cells derived from Brachet’s Cleft in Xenopus and zebrafish gastrulae "
Abstract
The ability of cells within an organism to move and rearrange into separate tissues is a defining feature of animals, but it is unclear how cells initiate and maintain their separation status. My objective is to determine how tissue separation is achieved at the cellular level between adhering embryonic cells. Brachet’s cleft is a naturally occurring example of tissue separation in Xenopus laevis and zebrafish gastrulae. Brachet’s cleft has cells of one type, the ectoderm, on one side, and cells of another type, the mesoderm, on the other. In a recent publication we report the existence of “slippery” adhesions between cells taken from either side of Brachet’s cleft, named cleft adhesions. We found that the cytoskeleton at the cell-cell contact between heterotypic cell pairs was not downregulated, as it was in homotypic cell pairs. We also found extracellular matrix (ECM) at cell-cell contact sites. My hypothesis is that adhesion between embryonic cells consists of 2 phases – an initial, weaker ECM-based adhesion, and a later, stronger cadherin-based adhesion – and that adhesion between homotypic cell pairs progresses normally to the second phase, but is halted between heterotypic cell pairs at the first phase. Using cells taken from Brachet’s cleft in Xenopus laevis and zebrafish I will study the kinetics and cellular basis of these cleft adhesions and compare them to cell-cell adhesion between homotypic cells.
Ramsay Wright is a wheelchair accessible building.
PhD Transfer Examination - Cariana Carianopol (Gazzarini lab)
PhD Transfer Examination
Thursday December 10th, 12:10 pm – 3087 Earth Sciences Centre
Carina Carianopol (Gazzarrini lab)
"Interaction between SnRK1 and ABA signaling pathways in Arabidopsis thaliana"
Abstract
Plants have developed intricate mechanisms to enable survival and propagation. Regardless of the type of stress, the result is energy deprivation that occurs through decreased photosynthesis and respiration rates. Energy sensors, which are conserved in yeast, mammals and plants, are activated in order to achieve energy homeostasis through metabolic compensation. In plants, the SnRK1 (Sucrose non-fermenting Related Kinase 1) members are the orthologs of the yeast Snf1 and mammalian AMPK energy sensors. The catalytic subunit of SnRK1, AKIN10, has been proposed to link stress, sugar and developmental signals in order to regulate plant metabolism, energy balance, growth and therefore survival of the plant under stress. Recent work indicates SnRK1 and ABA (abscisic acid) signaling pathways intersect during stress responses and share common transcriptional targets, however, the mechanism of this interaction is unclear. The aim of this project is to investigate mechanisms of growth and development regulation by AKIN10 and ABA in Arabidopsis thaliana. A high-throughput Y2H screen using AKIN10 against a collection of 258 ABA-regulated genes was performed resulting in 50 putative AKIN10 interactors, 39 of which were reconfirmed by Y2H. The list includes: 5 previously characterized AKIN10 targets; metabolic and regulatory proteins (kinases, phosphatases, etc.) and stress-related proteins; analysis of GO molecular function indicates this list is enriched for transcription factors.
PhD Transfer Examination - Debanjan Barua (Winklbauer lab)
PhD Transfer Examination
Monday December 7th, 2:10 pm - Ramsay Wright Building, Rm. 432
Debanjan Barua (Winklbauer lab)
" Characterizing the mechanics of tissue separation behaviour at
Brachet’s cleft during gastrulation in Xenopus laevis"
Abstract
Boundary formation between two distinct tissues is a crucial yet still poorly understood developmental process. In contrast to boundaries where cells are intimately attached, cleft-like boundaries allow for movement of tissues while preventing intermixing of the distinct tissues. During gastrulation of the anuran Xenopus laevis, involuting mesoderm cells migrate across the ectodermal blastocoel roof without intruding into the ectodermal cell layer, forming a cleft-like boundary called Brachet’s cleft. Although key molecular factors that play a role in the development and maintenance of Brachet’s cleft have been uncovered, little is known about the mechanics underlying this design. I have recently characterized intercellular contacts at the boundary and found that boundary cells exhibit: close contacts at intercellular distances compatible with cadherin mediated adhesion, intermediate contacts at much greater distances which may be regulated by the ECM, and large gaps, all of which under normal conditions are maintained at a particular ratio. My preliminary data suggests that these types of cell contacts at the cleft are not fundamentally distinct from cell contacts within the boundary tissues, however, there seem to be clear quantitative differences in contact type distribution and tissue cohesion between the ectoderm and mesoderm tissues. Thus, I hypothesize that separation behavior is asymmetric at Brachet’s cleft. More specifically, at the boundary, the mesoderm treats the ectoderm as if it were mesoderm and the ectoderm surface remains unchanged after coming into contact with the mesoderm. In order to test this hypothesis, I will investigate and characterize boundary mechanisms at Brachet’s cleft during gastrulation and present a model of the cleft based on quantifiable mechanics. I hope that my findings will establish a link between the molecular and mechanical aspects of cleft-like boundary formation and contribute to a more comprehensive understanding of this process.
Ramsay Wright is a wheelchair accessible building.