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CN2010 Exam 3 KEY - CN2010 Biol 5571 Exam 3 Key to test...

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CN2010 Biol 5571 Exam 3 Key to test questions. 1. Proper spatial architecture is critical to normal functioning of the nervous system. Explain briefly how patterning/segmentation is achieved rostrocaudally (anterior- posterior) and dorsoventrally in the developing vertebrate nervous system? (1/3-1/2 page maximum). Rostrocaudal patterning is determined by transcription factors such as Krox-20 and Hox genes; and signaling pathways initiated by receptor tyrosine kinases such as Sek-1-4 and their ligands Elf-2 . While Krox-20 and Sek-1 determine the overall architecture of segmentation, Hox genes determine the fate of these segments. The graded Hox gene expression is regulated by retinoic acid produced by Hensen’s Node. The dorsoventral patterning is regulated by sonic hedgehog secreted by the notochord ventrally and by bone morphogenetic proteins 4 and 7 (BMP-4/7) dorsally. 2. In as many ways possible, how will you make a growth cone turn? Very briefly outline the mechanisms underlying each strategy. (1/2 page max) 1. Cytochalasin B: destabilizes actin and GC turns away ( and in direction of stable F- actin) from point of cyto-B treatment. 2. Taxol and Nocodazole treatment: Taxol stabilizes microtubules (MTs) and growth cone turns towards direction of taxol treatment. Noco destabilizes MTs and turns away GC 3. cyclic nucleotides like cAMP and cGMP: can modulate extent of repulsive and attractive signal. Eg. High cAMP signal can make the GC turn towards a repulsive signal like netrin. Lowering cAMP levels in GC can make it turn away from an attractant. One mechanism is through regulation of polymerization of the cytoskeleton. 4. ECMs like laminin provide a better substrate for attachment of filopodia and enable GC to turn towards laminin. Laminin activates b-integrin signaling and is linked to the actin cytoskeleton.
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