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Ch. 18 - Post-transcriptional Regulation in Eukaryotes
Klug - Concepts of Genetics  12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
Chapter 18, Problem 24

We discussed several specific cis-elements in mRNAs that regulate splicing, stability, decay, localization, and translation. However, it is likely that many other uncharacterized cis-elements exist. One way in which they may be characterized is through the use of a reporter gene such as the gene encoding the green fluorescent protein (GFP) from jellyfish. GFP emits green fluorescence when excited by blue light. Explain how one might be able to devise an assay to test for the effect of various cis-elements on posttranscriptional gene regulation using cells that transcribe a GFP mRNA with genetically inserted cis-elements.

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1
Understand that cis-elements are specific sequences within an mRNA that influence its posttranscriptional regulation, such as splicing, stability, decay, localization, or translation efficiency.
Design a series of constructs where the GFP gene is fused with different candidate cis-elements inserted into its mRNA sequence at relevant positions (e.g., 5' UTR, coding region, or 3' UTR), ensuring that each construct contains only one variant of the cis-element to isolate its effect.
Transfect or introduce these GFP constructs into appropriate cells so that each cell population expresses GFP mRNA containing a specific cis-element variant.
Measure the GFP fluorescence intensity in each cell population using fluorescence microscopy or flow cytometry; differences in fluorescence levels will reflect changes in GFP protein expression caused by the inserted cis-elements, which can be linked to effects on mRNA stability, translation, or localization.
Complement fluorescence data with additional assays such as quantitative RT-PCR to measure GFP mRNA levels or RNA stability assays to distinguish whether changes in fluorescence are due to altered mRNA abundance or translation efficiency, thereby characterizing the functional impact of each cis-element on posttranscriptional regulation.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Cis-Elements in mRNA

Cis-elements are specific nucleotide sequences within an mRNA that influence its posttranscriptional fate, including splicing, stability, decay, localization, and translation. These elements act as binding sites for proteins or RNAs that regulate gene expression after transcription, making them crucial for fine-tuning protein production.
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Reporter Gene Assays Using GFP

Reporter gene assays use easily measurable genes like GFP to study gene regulation. By inserting cis-elements into the GFP mRNA, researchers can monitor changes in fluorescence as a proxy for how these elements affect mRNA processing or translation, enabling functional characterization of unknown regulatory sequences.
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Posttranscriptional Gene Regulation Mechanisms

Posttranscriptional regulation involves processes that control mRNA after it is made, such as splicing, stability, localization, and translation efficiency. Understanding these mechanisms helps explain how cis-elements influence gene expression levels and timing, which can be assessed by changes in reporter gene output.
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How is it possible that a given mRNA in a cell is found throughout the cytoplasm but the protein that it encodes is only found in a few specific regions?

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Incorrectly spliced RNAs often lead to human pathologies. Scientists have examined cancer cells for splice-specific changes and found that many of the changes disrupt tumor-suppressor gene function [Xu and Lee (2003). Nucl. Acids Res. 31:5635–5643]. In general, what would be the effects of splicing changes on these RNAs and the function of tumor-suppressor gene function? How might loss of splicing specificity be associated with cancer?

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Mutations in the low-density lipoprotein receptor (LDLR) gene are a primary cause of familial hypercholesterolemia. One such mutation is a SNP in exon 12 of the LDLR. In premenopausal women, but not in men or postmenopausal women, this SNP leads to skipping of exon 12 and production of a truncated nonfunctional protein. It is hypothesized that this SNP compromises a splice enhancer [Zhu et al. (2007). Hum Mol Genet. 16:1765–1772]. What are some possible ways in which this SNP can lead to this defect, but only in premenopausal women?

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