PhD Proposal Exam
Tuesday, June 27th, 2017 at 10:10 am – Earth Sciences Centre, Rm. 3087
Sonhita Chakraborty (Yoshioka lab)
“Investigation of the interplay between CYCLIC NUCLEOTIDE GATED ION CHANNEL 2 (CNGC2), Ca2+ and auxin signaling”
Cyclic nucleotide-gated channels (CNGCs) are non-selective cation channels that were first discovered in animals, where they were reported to be involved in visual and olfactory systems. While the biological role and channel properties of animal CNGCs have been well studied, not much is known about these channels in plants. The Arabidopsis thaliana CNGCs consists of twenty members, that have been implicated in development, ion homeostasis, thermotolerance, and pathogen defense. The “defense, no death” dnd1 and dnd2/hlm1, mutants of CNGC2 and CNGC4 respectively, exhibit autoimmune phenotypes such as dwarf morphology, constitutive expression of PR genes and elevated salicylic acid (SA) levels. To elucidate CNGC2-mediated signaling, repressor of defense no death 1 (rdd1), the first suppressor of dnd1 was identified. rdd1 is a loss-of-function mutation in YUC6, an auxin biosynthesis gene. Recent data shows that dnd1 has alterations in auxin signaling and auxin-induced Ca2+ flux. I hypothesize that CNGC2 is involved in development and auxin signaling in addition to its role in plant immunity. The aim of this project is to understand CNGC2-mediated signaling by elucidating the mechanism by which rdd1-1 supresses dnd1. YUC6 is involved in auxin biosynthesis and ROS homeostasis. Hence, I will explore if the suppression of dnd1 is through either of these functions. CNGC2 might also be important for auxin transport. Results from this project will provide new insights into the role of auxin in CNGC2 and Ca2+ signaling in the context of plant immunity.
PhD Proposal Exam
Tuesday May 16th, 10:10 am – Ramsay Wright Building, Rm. 432
Annik Yalnizyan Carson (Richards lab)
“Episodic Control: The Role of Memory Systems in Decision Making”
Reinforcement learning (RL) is an area of machine learning concerned with optimal behavioural control. RL provides a normative framework in which to understand how the brain can learn to make decisions for maximizing subjective reward in the absence of an explicit teaching signal. Currently, even agents using state-of-the-art control systems in RL tasks are data inefficient and challenged by nonstationary environmental conditions, including changes in statistics of reward probability and transitions between states, which biological agents handle with relative ease. It has been proposed that storing information about experienced episodes in a memory cache — modeled after the activity of the hippocampus in animals — can help bootstrap learning in RL systems to improve the speed of learning and ability to cope with nonstationary environments. My research proposes three different representations for episodic memories stored in such a system and aims to resolve which provides the greatest benefit to RL systems when used in conjunction with a standard controller. Furthermore I aim to resolve how these representations can account for features of animal behaviour, and which of these representations — if any — are likely to explain how episodic memory is represented in the hippocampus.
Ramsay Wright is a wheelchair accessible building.
PhD Proposal Exam
Tuesday May 2nd, 2:30 pm – Rm. CCT 3150, University of Toronto at Mississauga
Abiramy Karunendiran (Stewart/Barzda labs)
“Investigating the Role of Sarcomere Structure and Bioenergetic Input on Muscle Contraction in Drosophila Using Nonlinear Optical Microscopy“
Nonlinear optical microscopy has been shown to be a superior imaging modality compared to fluorescence and electron microscopy. Imaging can be done without prior staining, providing a variety of valuable techniques that can be used to reveal structural and functional information in a biological system. Second harmonic generation is observed in non-centrosymmetric cylindrical molecules such as myosin and can be used to directly visualize muscle structure. It was found through polarization microscopy that the second harmonic signal is generated from the anisotropic bands. Hence, the objective of this research is to investigate dynamic properties of sarcomere structure as well as genetic and bioenergetic inputs in Drosophila Melanogaster muscles. This will be accomplished using three approaches. Recently, it was found that the second harmonic response was affected by the size of the sarcomere. To further characterize the second harmonic properties of muscle, changes in the SHG response as well as polarization dependency on myofibril organization will be investigated at various elongation lengths. These parameters will also be compared in somatic, cardiac and visceral muscles to investigate the changes in SHG response due to changes in myofibril organization. The technique will then be applied to examine changes in second harmonic properties of sarcomere due to presence/absence of various chaperones and co-chaperones responsible for thick filament maintenance. Lastly, THG intensity changes due to activity of mitochondria will be investigated along with its correlation to sarcomere contractions. This imaging technique offers new perspective on the dynamic properties of contraction, and how these properties may be altered in movement disorders.