PhD Proposal Examination – Abiramy Karunendiran (Stewart/Barzda labs)

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

Abstract

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.

PhD Proposal Examination – Christine Nguyen (Stewart lab)

PhD Proposal Examination

 

Friday April 21st, 1:10 pm – Room CCT 2150, University of Toronto at Mississauga

 

Christine Nguyen (Stewart lab)

The Characterization of the Electrophysiological Properties of Three-Dimensional Bioengineered Human Skeletal Muscle and Neuromuscular Junctions

 

Abstract

Two-dimensional (2D) in vitro models of human skeletal muscle lack the architecture and contractile properties of a native muscle fiber, limiting them from being used for in vitro neuromuscular junction (NMJ) experimentation. A new method for creating three-dimensional (3D) human skeletal muscle tissues from human primary myogenic progenitors has been reported. The bioengineered muscle tissues are contractile, mimic’s clinical responses to drugs, and possess the epilson acetylcholine receptor (AChR) unit expressed in mature NMJs. Central to the communication of neurons and cells is the synapse, where transmission occurs via electrical and chemical signals between the close apposition of the pre- and post-synaptic cell membrane. At the vertebrate NMJ, acetylcholine is released from the pre-synaptic nerve terminal where it binds to AChRs on the postsynaptic muscle fiber. The flow of cations into the postsynaptic muscle cell induces a change in the membrane voltage that activates the muscle. The characterization of electrical properties of the muscle cells at rest, and when excited is crucial to advancing our understanding of the bioengineered muscles functionality. This proposed thesis will characterize the electrical properties in vitro 3D skeletal muscle tissue, and use it as the foundation for studying synaptic transmission of skeletal muscle tissues co-cultured with human pluripotent stem cell (hPSC) derived motor neurons (MN). Duchenne’s muscular dystrophy (DMD) is a fatal muscle disorder involving the skeletal muscle system. Little is known regarding the functional properties of the NMJ in DMD patients due to difficulties of in vivo experiments, and the lack of in vitro models. A new in vitro system of the NMJ will allow for further analysis in studying the integrity of skeletal muscles with regards to neuromuscular activity. Electrophysiological analyses of the model NMJ will be studied in both normal muscle cells, as well as in mutant cells with DMD.

 

PhD Proposal Examination – Samantha Lauby (McGowan lab)

PhD Proposal Exam

 

Thursday April 6th, 10:10 am – Earth Sciences Centre, Rm. 3087

 

Samantha Lauby (McGowan lab)

Thyroid Hormones and Tactile Stimulation in Early-Life:  An Investigation of Mechanisms Mediating Later-Life Stress Responses

Abstract

The stress response must be flexible in order to respond to a varying environment. It is also evident that the quality of care received in early life can affect later life stress responses in a long-term manner. In rodent models in the laboratory, handling by an experimenter early in life appears to optimally prepare pups for moderately stressful testing conditions in adulthood. Tactile stimulation provided by the mother in early life also appears to program stress-related responses in later-life. The thyroid system has been proposed to constitute a mechanism signaling these early life events.  To investigate their interaction, I will use a 2×2 study design, with supplemental tactile stimulation and manipulating ambient temperature during separation, during an early-life handling procedure in rats. I will then identify changes in thyroid hormone activity in circulating blood and brain tissue. In addition, I will examine behavioural, physiological, and transcriptional components of stress-related responses in these offspring. Finally, I will characterize mechanisms that underlie identified gene expression changes. I hypothesize that the effects of supplemental tactile stimulation depend on a drop in body temperature with a subsequent release of thyroid hormone. This research will elucidate biological mechanisms by which animals adapt to their environments and outcomes related to a match or mismatch between early-life programming and the later-life environment.