PhD Exit Seminar
Wednesday, November 22, 2017 at 2:10 pm, SW 403 – University of Toronto at Scarborough
Wilfred Carlo de Vega (McGowan Lab)
“DNA Methylation Modifications Associated with Glucocorticoid Sensitivity and Clinical Subtypes of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome”
Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a complex chronic disease with an unknown etiology that is primarily characterized by the presence of a highly debilitating fatigue that fails to resolve after sufficient rest. Additionally, patients must present other nonspecific symptoms relating to pain, unrefreshing sleep, cognitive impairment, and autonomic dysregulation in order to be diagnosed with ME/CFS, resulting in a population with highly heterogeneous symptom profiles. Previous research has consistently observed long-lasting changes in the immune system and hypothalamic-pituitary-adrenal (HPA) axis, a neuroendocrine system that regulates stress response. As a prototypical medically unexplained disease, environmental factors are believed to play a major role in the onset and manifestation of ME/CFS symptoms. These enduring differences may be partly explained through epigenetic modifications, referring to heritable gene expression alterations in the absence of mutations, which are known to reflect environmental, genetic, and stochastic influences on gene expression. This thesis explored the epigenetic modifications associated with the immune and neuroendocrine differences in ME/CFS. Specifically, DNA methylation across the genome was examined in peripheral blood mononuclear cells of ME/CFS patients, and immune response was tested by measuring in vitro sensitivity to glucocorticoids, a class of hormones that serve as an HPA axis effector. Differential methylation in ME/CFS was significantly enriched in immune response and cellular signaling genes, and was localized to 4,699 sites, which may serve as potential biomarkers. Two ME/CFS immune subtypes were observed according to glucocorticoid sensitivity. Integration of methylation and clinical data via machine learning discovered 4 clinical subtypes that were differentiated by T cell response genes, physical functioning, and post-exertional malaise. These results suggest that DNA methylation modifications are a feature of ME/CFS pathology. The identified potential biomarkers and clinical subtypes may be implemented in future work to better understand and clarify the biological differences related to specific ME/CFS symptoms.
PhD Exit Seminar
Monday November 20th, 2:05 pm – Ramsay Wright Building, Room 432
Heather Wheeler (Campbell lab)
Cellulose Biosynthesis has Extensive Impacts on Overall Plant Metabolism, Which are Mediated in Part by Pentaglycine, a Novel Peptide Signal
As sessile organisms, plants must continually adapt to their environment. In order to allocate resources appropriately, plants have elaborate pathways in place for detecting and responding to changes in their environment and the integrity of their cells, particularly the cell wall. Cellulose is the major component of plant cell walls and a major sink for carbon in the plant body. Cellulose is central to plant structure and function, imparting sufficient strength and resilience to withstand turgor pressure, negative pressure, and gravity. It was therefore hypothesized that plants have broad, far-reaching metabolic responses to cellulose disruption.
To uncover the response to cellulose perturbation at the metabolic level, Comprehensive Multiphase-Nuclear Magnetic Resonance (CMP-NMR) was used in combination with a mutant analysis and pharmacological experimentation. This approach revealed several metabolic impacts of cellulose perturbation that were previously unknown, including decreased metabolism of seed lipid stores during germination, increased production of methanol and ethanol in seedlings, and the presence of pentaglycine in seedlings.
Another line of investigation revealed that a compound or compounds present in the cellulose synthase mutant eli1 was able to increase lignin content of wild-type seedlings. Pentaglycine had a similar effect on WT seedlings. Taken together with the increased abundance of pentaglycine in eli1 seedlings, the results suggest that pentaglycine is in part responsible for the increased lignin content that characterizes cellulose synthase mutants. A model is presented that integrates these components into a signaling pathway to monitor and respond to perturbation in the cellulosic component of cell wall integrity.
PhD Exit Seminar
Friday October 6th, 11:10 am – Ramsay Wright Building, Room 432
Jason Wen (Winklbauer lab)
“Endoderm internalization in Xenopus laevis, and the role of ephrinB1 in gastrulation”
During animal development, the early embryo undergoes gastrulation to pattern the primary germ layers. The ancestral mode of vertebrate gastrulation can be studied using the African clawed frog Xenopus laevis. A core function of gastrulation is the movement of prospective endoderm from the surface to the embryo interior. In X. laevis, endoderm internalization is achieved through vegetal rotation, a morphogenetic process that has only been characterized at the tissue level. I have investigated the cell and molecular basis of endoderm morphogenesis in X. laevis gastrulae to connect vegetal rotation with common mechanisms of germ layer internalization in other organisms. I characterized the arrangement, shape change, and migration of cells in the endoderm and found that movement of vegetal endoderm cells located deep to the embryo surface represents an adaptation of mechanisms of epithelial internalization, particularly invagination and cell ingression, to the multilayered structure of the vegetal cell mass. Thus, this movement was termed “ingression-type migration”. Ingression-type migration integrates amoeboid-type motility, whereby cells propel forward using cell shape changes to generate locomotion, with cell tail retraction by macropinocytosis. In conjunction with differential migration — a mode of intercellular migration where cells move in a common direction but at different velocities with respect to neighbouring cells — this drives cell rearrangement during vegetal rotation. Despite their collective movement, endoderm cells are separated by vast gaps filled with extracellular material. Cells are interconnected by stitch-like contacts, and cell migration requires the adhesion molecule C-cadherin, and the matrix protein fibronectin. A basic requirement for migration is that cells must detach to complete rearrangement, and in this regard, the leading cell resolves its contact with the following cell through trailing edge retraction involving ephrinB1-dependent macropinocytosis and trans-endocytosis. Beyond the endoderm, ephrinB1 is also required for the modulation of ecto- and mesoderm tissue cohesion.