pset7S - Solution Key 2010 7.012 Problem Set 7 Question 1...

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1 Solution Key - 2010 7.012 Problem Set 7 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? A morphogen is a regulatory factor, either an inducer or a determinant, which regulates the fate of cells during development in a concentration dependent manner. b) Assume that the cells below are producing and responding to EGF. i. Which cells produce the EGF ligand? Inducing cells ii. Which cells produce EGF receptor? Responding cell iii. In which cells is the MAP kinase cascade activated? Responding cell iv. In which cells will the activation of MAP kinase cause target gene expression? Responding cell v. What type of morphogen ( inducer/determinant ) is EGF? Explain your choice. EGF is a ligand secreted by the inducing cells. It induces the responding cells to acquire a specific cell fate by binding to specific receptors on their surface and activating the MAPK kinase cascade. So EGF is an inducer. Unlike an inducer, a determinant is a cell autonomous regulatory factor, which is never secreted. 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? Regulatory, effector and ubiquitously expressed genes in a specific cell make the combinatorial code of that 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? No since the schematic represents the embryonic spinal cord prior to differentiation. be a ubiquitous gene? Possibly NKX2.2, it is expressed in all three neurons. However, the NKX2.2 expression in non-spinal cells should be looked at to come to a conclusion.
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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 4 II motor, sensory, lateral, hippocampal 1 III sensory, lateral, hippocampal 2 IV motor, sensory 3 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.
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pset7S - Solution Key 2010 7.012 Problem Set 7 Question 1...

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