PhD Transfer Exam – Abdiwahab Moalim (Plotnikov lab)

PhD Transfer Exam

 

Tuesday May 30th, 1:10 pm – Ramsay Wright Building, Rm. 432

 

Abdiwahab Moalim (Plotnikov lab)

Investigating the role of focal adhesion-localized calcium sparks in the sensing of extracellular matrix mechanical properties

Abstract

The ability of cells to sense and to respond to mechanical cues in their environment such as extracellular matrix (ECM) stiffness underlies crucial physiological processes ranging from embryo development and stem cell differentiation to tissue homeostasis. This ability also plays a key role in pathological processes such as atherosclerosis and cancer metastasis. Despite their apparent biological and clinical significance, the molecular mechanisms that allow cells to probe ECM stiffness are currently elusive. I have recently begun to investigate how calcium signalling at integrin-based focal adhesions (FAs), sites of cell-ECM contract, mediates the ability of mouse embryo fibroblasts (MEFs) to sense mechanical cues. I demonstrated that FAs are centres of transient calcium oscillations and showed that the oscillations are controlled by actomyosin contractility and ECM stiffness. Through pharmacological perturbations I further showed that these oscillations are due to extracellular calcium entry through stretch-activated ion channels. I hypothesize that actomyosin forces open stretch-activated channels located within FAs in an ECM-stiffness dependent manner and that this signal is used as a readout for ECM stiffness. In my doctoral work, I plan to describe the distribution of calcium sparks in the focal adhesions of cells in a diversity of in vitro and in vivo mechanical environments, identify the particular stretch-activated channels responsible for these sparks, and elucidate other FA constituents that modulate spark behaviour. This work is anticipated to further our understanding of how cells interpret and navigate complex mechanical environments experienced by cells in both physiological conditions and disease.

Ramsay Wright is a wheelchair accessible building.

 

 

PhD Transfer Exam – Morley Willoughby (Bruce lab)

PhD Transfer Exam

 

Wednesday May 24th, 10:10 am – Ramsay Wright Building, Rm. 432

 

Morley Willoughby (Bruce lab)

Investigating the Role of the Small GTPase Rab25 during Zebrafish Epiboly”

Abstract

The adult body plan of an organism is established during a process called gastrulation. Despite the diversity of organisms across the animal kingdom, gastrulation occurs through a limited number of dynamic, large scale cellular movements. Epiboly is a conserved morphogenetic movement that is defined as the thinning and expansion of a cellular sheet. Understanding the molecular mechanisms that control this process is critical to our understanding of developmental biology. The small GTPase Rab25 becomes upregulated at the onset of zebrafish epiboly.  Rab25 is a member of the Rab11 subfamily of GTPases, and is known to direct apical vesicle trafficking and transcytosis in polarized epithelial cells. Rab25 morpholino knockdown or knockout using CRISPR/Cas9 gene editing technology results in an epiboly delay during zebrafish morphogenesis. Remarkably, while rab25 expression becomes restricted to the enveloping epithelial layer (EVL), a single cell thick epithelium during epiboly, the underlying loosely packed deep cells exhibit a larger epiboly delay. I hypothesize that the small GTPase Rab25 functions in the EVL during zebrafish epiboly. I propose to use the CRISPR/Cas9 Gene Editing technology to create an endogenous Rab25 fusion protein in the zebrafish genome to examine the intracellular localization of Rab25 in live embryos. I will then characterize defects within the EVL of Rab25 mutant embryos to understand how aberrant vesicle trafficking is leading to the observed epiboly delay. It is anticipated that my project will help uncover the relatively unknown molecular mechanisms controlling epiboly.

Ramsay Wright is a wheelchair accessible building.

 

PhD Transfer Exam – Bradley Laflamme (Desveaux/Guttman labs)

PhD Transfer Exam

 

Tuesday May 23rd, 1:10 pm – Earth Sciences Centre, Rm. 3087

 

Bradley Laflamme (Desveaux/Guttman labs)

 

“Identifying new building blocks of type III effector-mediated virulence using the Arabidopsis-Pseudomonas syringae pathosystem”

 

Abstract

 

Pseudomonas syringae is a Gram-negative bacterial pathogen which infects many plant species, including the model plant Arabidopsis. The virulence of this pathogen requires its type III secretion system, which is used to inject a collection of “effector” virulence proteins directly into host cells to evade immunity and improve pathogenesis. While each strain of P. syringae is virulent on only a small number of hosts, effectors isolated from phylogenetically diverse strains often still have virulence functions in non-hosts, reflective of the fact that they target conserved facets of immunity across plant species. However, the vast majority of diverse effector variants across all sequenced P. syringae isolates have no characterization in terms of how they contribute to virulence in any plant background. To address effector-mediated virulence as a broad phenomenon, our labs have begun developing a type III effector compendium (T3EC) which collects effector sequences from across diverse isolates as a resource for wet-lab experiments. Using several pathogenicity assays which characterize effector-mediated virulence in distinct ways, we plan to screen and annotate the T3EC for virulence activity in Arabidopsis. After identifying effectors which contribute to particular aspects of P. syringae virulence, we will then explore synergistic relationships between these effectors, with our final goal being to develop a novel pathogen of Arabidopsis with a profile of synergistic effectors not found in any naturally occurring strain. This project will elucidate how effectors involved in targeting distinct immune processes intersect and amplify one another to dismantle plant immunity in successful pathogens.