pset7-draft_3

pset7-draft_3 - Name_ Section_ TA_ 2010 7.012 Problem Set 7...

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Name_____________________________________ Section_______ TA_____________ 1 2010 7.012 Problem Set 7 Please print out this problem set and answer the questions on the printout. Answers to this problem set are to be turned in at the box outside 68-120 by 1:15 pm, Friday Nov 19 th . Question 1 The MAP kinase cascade is activated by Epidermal Growth Factor (EGF) signaling. This pathway is used during development to induce various cell fates. a) EGF can act as a morphogen. What is a morphogen? b) Assume that the cells below are producing and responding to EGF. i. Which cells produce the EGF ligand? ii. Which cells produce EGF receptor? iii. In which cells is the MAP kinase cascade activated? iv. In which cells will the activation of MAP kinase cause target gene expression? v. What type of morphogen ( inducer/determinant ) is EGF? Explain your choice. c) Which class of genes ( regulatory/effector ) is expressed when an uncommitted cell becomes committed? d) Which class of genes ( regulatory/effector ) is expressed when a committed cell differentiates ? e) What are the three classes of genes that make the combinatorial code of a differentiated cell? A schematic of the embryonic spinal cord , prior to any differentiation , is shown below. Regulatory factors expressed in the cells of each region are indicated, as are the fates of the cells in these regions. Inducing cell Responding cell Express Pax7 and NKX2.2 proteins, future sensory neurons Express NKX2.2 proteins, future inter neurons Express FoxA2 and NKX2.2 proteins, future motor neurons f) Based on the information in this schematic, could any of these genes (Pax7/NKX2.2/FoxA2) be an effector gene? be a ubiquitous gene?
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Name_____________________________________ Section_______ TA_____________ 2 Question 2 A major goal of stem cell research is to repair diseased brains using neural stem cell lines. Four human embryonic cell lines, originally prepared from the SAME embryo , were tested for their potency in vitro , after exposure to retinoic acid, which promotes differentiation of all neuronal fates. Cell line Neuronal types differentiated in vitro Potency (1=most potent) I motor II motor, sensory, lateral, hippocampal III sensory, lateral, hippocampal IV motor, sensory a) Based on the data above, complete the table by ranking the neuronal potency of these cell lines. b) Complete the lineage tree below using the information in the table. c) Does each of these cell lines have the same DNA sequence? Explain . d) In a living organism (
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This note was uploaded on 03/12/2011 for the course BIO 7.012 taught by Professor Lander during the Fall '10 term at MIT.

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pset7-draft_3 - Name_ Section_ TA_ 2010 7.012 Problem Set 7...

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