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University of Toronto St. George
Cell and Systems Biology

CSB428H1F FINAL EXAMINATION 2009 ANSWER KEY #1: Langevin et al. Central questionhypothesis What is the role of the exocyst complex, specifically Sec5, in delivery of DE-CadArm to the plasma membrane from the recycling endosome and how do they interact with RE components such as Rab11? Main conclusion Drosophila Sec5, Sec6 and Sec15 tethers DE-Cad vesicles originating from the RE to lateral membrane for exocytosis. Sec5 also mediates transcytosis of DE-Cad. In addition, Arm interact with Sec10 at PM and Arm act as a landmark for DE-Cad delivery. In the absence of Sec5, Sec6 and Sec15 function, DE-Cad accumulates in an enlarged RE. Key experiment sec5 mutant notum cells generated using FLPFRT were analyzed for different intracellular markers to investigate the nature of the enlarged intracellular compartment. Golgi marker Lava Lamp, late endosome marker Hepatocyte growth factor-Regulated tyrosine kinase Substrate, early endosome marker Rab5 was distributed normally in mutant cells. But Rab11 distribution was disrupted in mutant cells: they were found in large punctate structures with higher intensity of Rab11 and colocalized with DE-Cad in RE. Additional RE maker Nuclear Fallout confirmed this result. This shows Sec5 is necessary for the recycling of DE-Cad from RE to the lateral membrane Criticismfuture direction Investigate possible interaction between components of the exocyst complex with the cell cytoskeleton. Specifically, MT have been known to play a role in vesicular trafficking, and the authors could investigate if disruption of MT also disrupts delivery of DE-Cad to lateral membrane and establishment of AJs. MT could be disrupted by drugs such as nocodazole or knockdown of XMAP215. #2: Chaung et al. 1 www.notesolution.com
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