The role of the motor protein, kinesin heavy chain, in Drosophila bristle development. Yasmin Simkhoni, Uri Abdu. Department of Life Sciences, Ben-Gurion University, Beer-Sheva, Israel.

   Drosophila bristles serve as a good model to understand the role of cytoskeleton fibers in polarized cells. Previously it was shown that mutation in microtubule (MT) plus end motor protein, kinesin heavy chain (khc), affected bristle morphology. Previous study revealed that null mutation of khc resulted in short bristles, as well as flattened, flared, or twisted tips compared to WT. Another phenotype that has been demonstrated was a thinner cuticle of the bristle. In this study we would like to understand the molecular mechanism by which khc affects bristle growth. We show that knocking down khc specifically in the bristle by RNAi leads to defects in bristle tip morphology accompanied with uneven distribution of MTs at the bristle tip. We found that in khc RNAi knockdown flies the function of MTs within the bristle was not affected. Tracking of MTs polymerization using GFP-EB1 (End Binding protein 1) revealed an area that lacked microtubule movement, which suggested that a physical barrier at the bristle tip might have blocked MT distribution. To identify the nature of this physical barrier at the bristle tip, we first characterized the organization of mitochondria, golgi and ER within the bristle cell. We demonstrated that mitochondria were localized at the bristle cell base as well as along the entire bristle shaft. Moreover, live imaging of mito-GFP revealed stationary, anterograde and retrograde movements within the bristle shaft. Whereas Golgi and ER were localized mostly to the bristle cell body, Golgi outposts were found at the lower part of the bristle shaft and ER was evenly distributed along the bristle. Our future plans are to study the effect of khc RNAi downregulation on the organization of the above organelles.