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UBC Theses and Dissertations

Morphological characterization of dynamic dendrite growth in the awake developing brain Hossain, Sharmin


Precise wiring between dendrites and axons during brain development is a critical requirement for forming proper neuronal connectivity, a prerequisite to generate correct brain function. Establishing this highly complex physical network entails forming precise patterns of dendritic and axonal arborization as well as correct targeting of these processes to appropriate brain regions. As compared to our current understanding of axonal development, relatively little is known regarding the structural organization and of dendritic arbor growth during dendritogenesis. Two major obstacles in studying dendritogenesis in vivo are technical challenges in observing the dynamic behavior of these structures in the developing brain, and post-imaging analyses of their complex growth patterns. Here, we used in vivo rapid time-lapse imaging in the intact and awake vertebrate brain to observe dynamic dendritogenesis and analyzed components of growing dendritic arbors of individual neurons to elucidate how short-term growth behaviors culminate to produce the dendritic arbor patterning of mature neurons. Of particular interest, this work establishes that dendritic growth cones exist on all growing dendrites, but due to their dynamic nature, they have been grossly under-reported in previous in vivo studies. In this study, I find that dendritic growth cone morphology correlates with branch behavior, report differences in two different dendritic filopodial populations in vivo, and describe how dendritic growth behavior changes over neuronal maturation. Further, we have developed a novel analysis tool called Dynamo to accurately track and analyze dendritic components. I have used this tool to screen three candidate guidance cue molecules, including ephrin-A1, ephrin-B1, and slit2, for their potential role in regulating dynamic behavior of growing dendrites, and found that slit2 exposure decreases branch motility and increases branchtip filopodial motility in vivo. I also find that neurons located in the caudomedial tectum project their dendrites in a biased rostral orientation to reach the tectal neuropil, and that interfering with the Slit receptor Robo3, prevents this biased dendrite growth. These findings provide novel insights into how dendrites develop in vivo in the awake vertebrate brain.

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