Bio 363 Human Genetics Spring 2013
Marfan Syndrome study sheet
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Background readings (including textbook chapters and
Ramirez and Dietz review paper)
What are the symptoms, diagnostic criteria, and treatments for Marfan Syndrome?
What genes are associated with the syndrome? What do they encode? What are the roles of the gene products?
The old standard view of Marfan was that defective fibrillin led directly to weaker connective tissue simply because fibrillin is a component of extracellular matrix. How has our overall view become more complex regarding the mechanisms underlying Marfan syndrome?
How might you explain the variability in symptoms seem in different patients?
What is the general idea of recombination mapping? In humans, what genetic markers are used?
Why do you need "informative meioses" to do linkage analysis?
What are lod scores? How are they calculated? How are they used? (we will do an exercise in class on this topic)
Kanulainen et al. 1990
What was the goal of this paper? What was known prior to this study?
What approach did the authors take? Who were their subjects?
Figure 1: what do the plusses and minuses mean? (The authors don't word their explanation very well)
How is the diagnosis of each individual depicted?
Can you deduce the genotypes of any of the individuals for which the genotype is not shown?
Which of the three markers is not completely linked to the disease? Which individuals tell you that?
How does Table 1 relate to Fig 1?
How does Fig 2 relate to Table 1?
What are the general difficulties encountered in trying to map a disease gene by linkage analysis?
For what did this study set the stage?
Dietz et al., 1991
What converging approaches led to this study?
How does Fig 1 correspond to what we saw in the previous paper?
Fig 2: What was the goal here? What is SSCP analysis? Why does only one patient show a difference?
Explain what specific mutation was found in patient E.S. (text and Fig 3A-B). Do you automatically assume that that mutation causes the disease? What other experiments were done (e.g. Fig 3C)?
How does gene homology in other species support the conclusion?
What do the authors speculate regarding Marfan mutations in other families?
Neptune et al., 2003
Be ready to verbally annotate each figure with regard to genotypes, tissues, ages of mice, types of microscopy, stains used, axes on graphs, etc.
Fig 2: What does the presence of surfactant protein 2 indicate? What alternative explanation for the overall finding does this rule out?
Fig 3: Why is it noteworthy that fibrillin resembles in sequence the LTBP group of proteins? What does that suggest fibrillin might do?
In Fig 3b-c, focus on the red staining (the blue just shows cell nuclei). The following information from the text is important: TGF-beta and LAP-beta 1 are originally part of the same translated protein that is cut into those two pieces. The pieces stay together (noncovalently) as the protein is secreted out of the cell and sequestered (stuck) on the extracellular matrix. At some point, just the TGF-beta portion is "activated" or loosened and separated from LAP-beta 1 and the extracellular matrix. Only then can it go and bind to its receptor on other cells. The antibody used in the top panels of Fig 3b binds only to the activated form of TGF-beta.
Fig 3d: What is special about the DNA sequence CAGA?
Fig 3e-f: What is the dramatic result and its meaning? Is there another control experiment that should have been done here?
Fig 4: How was the neutralizing antibody administered? (May need to check Materials and Methods)
Fig 5: What were two possibilities for why mutant lungs had larger air pockets and fewer cells? What molecular readouts for each phenomenon were examined?
Fig 6: Why did the researchers have to look at a different mouse strain?
Why doesn't this paper have separate Introduction, Results, and Discussion sections?