Mack, DavidWatson, Cecelia Jean2023-09-272023-09-272023-09-272023Watson_washington_0250O_26245.pdfhttp://hdl.handle.net/1773/50696Thesis (Master's)--University of Washington, 2023Abstract: Intrafusal fibers of the muscle spindle play an essential role in the reflex circuits that regulate muscle contraction in response to strain. Dysfunction of the muscle spindle is suggested to contribute to the impaired proprioception and ataxic behavior seen in muscular dystrophies and other neuromuscular disorders. The molecular mechanism by which these disorders impair muscle spindle function has yet to be determined. This is partly due to the scarcity of intrafusal fibers in the body, and therefore the difficulty of isolating these cells via biopsy. This limited availability of appropriate muscle spindle models has led to a lack of study of these structures in neuromuscular research. Research regarding the muscle spindle and intrafusal fibers to-date has largely relied on murine cells. In the small body of work so far performed using human cells, de novo generation of intrafusal fibers has only been attempted in 2D for short periods of time. This project used new technology to create 3D engineered muscle tissues (EMTs) from human induced pluripotent stem cells and investigated the effects of treatment with Neuregulin-1, which is known to drive intrafusal fiber formation in vivo. The effect of Neuregulin-1 treatment was characterized using immunofluorescence and longitudinal analysis of EMT contraction kinetics. This research represents a new model for studying intrafusal fiber and muscle spindle generation, the first to thoroughly investigate previously published differentiation protocols in 3D for over 30 days. The results of this study provide the most in-depth analysis of intrafusal fiber formation in vitro to-date. These data are invaluable to better understanding the development of proprioceptive function in skeletal muscle and will facilitate follow-on studies regarding the role of defective strain sensing in neuromuscular disorders such as DMD.application/pdfen-USnoneMuscle SpindleTissue EngineeringBioengineeringBioengineeringThesis