Regulation of Sensory Bristle Development in Drosophila Melanogaster by the Small GTPase Rab11

Nagaraj, Ranganayaki, Department of Biology, University of Virginia
Adler, Paul, Department of Biology, University of Virginia
Schafer, Dorothy, Department of Biology, University of Virginia
Cronmiller, Claire, Department of Biology, University of Virginia
Macara, Ian, Department of Microbiology, University of Virginia
Keller, Ray, Department of Biology, University of Virginia

Sensory bristles of Drosophila melanogaster are polarized single cell extensions whose shaft extends anywhere between 70m (microchaetes) and 250m (macrochaetes). Owing to the nature of their polarized structure, they have been useful model systems to study the role of cytoskeleton in cellular morphogenesis. Most of the previous work to understand bristle growth has focused on understanding how actin filaments are assembled and positioned to cause cell shape changes during their development. This dissertation describes my work in understanding the role of dRab11, a small GTPase, in bristle development. I show that disrupting rab11 function using rab11dsRNA results in adult bristles that are short knob like structures. rab11 hypomorphs also display shortened bristles with deformed tips. Live imaging studies show that upon disruption of rab11 function, bristles elongate, but at a slower rate than wild type bristles. At a late stage in elongation rab11 mutant bristles start to bulge at various positions along the shaft. These deformities become more severe over time and the bristles eventually collapse. This collapse is the cause of the small bristle stubs seen in the adult. The initiation of bristle breakdown coincides with the timing of actin breakdown that normally occurs during bristle development. However, bristles from rab11 mutants show dramatic alterations in the formation and organization of chitin bundles suggesting that Rab11 maintains bristle stability by mediating the formation of the chitinous bristle exoskeleton. My analysis of Rab11 localization in bristle cells shows that GFP-Rab11 accumulates at the tip of growing bristles, in addition to localizing along the bristle shaft. ii This localization pattern of GFP-Rab11 is microtubule dependent and occurs at early stages of bristle elongation. Microtubules function to promote bristle elongation. My observations show that microtubules are polarized in bristle cells with their minus ends towards the tip and plus ends towards the cell body. I confirm observations from previous studies showing that microtubules are required for bristle growth.

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PHD (Doctor of Philosophy)
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