Deep Question 4: Retinitis pigmentosa is a genetic disease that causes the break

by | Sep 18, 2022 | Biology | 0 comments

Deep Question 4: Retinitis pigmentosa is a genetic disease that causes the breakdown and loss of retinal cells. Retinitis pigmentosa often starts with decreased night vision and gradually progresses to blindness as retinal cells die. Several genes have been linked to Retinitis pigmentosa, one of which is GADD.
CRX is a key retinal transcription factor. CRX binds cis-acting regulatory elements called CBRs (CRX-binding regions). You are studying expression of the GADD* gene. Two CBRs are involved in regulating expression of the GADD gene. One CBR (CBR1) is immediately proximal (close) to the transcription start site (TSS). The other CBR (CBR2) is a few thousand base pairs upstream of the TSS.
You have received DNA from three patients with Retinitis pigmentosa. None of the patients have mutations in the coding region of GADD. Instead, all the mutations you find are in the CBRs: Patient 1 – Mutation in CBR1 Patient 2 – Mutation in CBR2 Patient 3 – Mutation in both CBR1 and CBR2
Using the DNA sequences from each of the patients and the luciferase gene (the protein produced by luciferase is what makes fireflies “glow”) you do a reporter assay. In this assay you measure the amount of luciferase protein produced by the regulatory regions from each patient’s Gadd DNA in different cell lines. The luciferase assay results are below. Note, results are relative to wildtype/unmutated Gadd gene: CBR1 mutation (Patient 1): 70% (i.e., 70% of wildtype/unmutated levels of product) CBR2 mutation (Patient 2): 60% Both CBR1 and CBR2 mutations (Patient 3): 20%
. This question is about gene regulation (that is, the results from the assay), not the luciferase assay itself. 300 words max (combined 1 and 2)
If you were to measure GADD protein levels in the three patients, would you expect them to be lower or higher than normal (normal = level in people without mutations in this region)?
What type of transcription factor is CRX? How do you know? Clearly explain your reasoning for (1) and (2)

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