Explain exactly what the X25 probe is and how it allows for visualization of mRNA from the patients. Include in your answer why GAPDH was also analyzed.
Friedreich ataxia (FRDA) is an autosomal recessive, neurodegenerative disease that causes a lack of voluntary coordination of muscle movements. Affected individuals are homozygous for an unusually large number (expansion) of repeats of a trinucleotide sequence (GAA) in the first intron of the X25 gene. Unaffected individuals typically have between 7 and 38 repeats of the trinucleotide (GAAGAAGAAGAA…). FRDA patients have anywhere from 66 to over 1,700 repeats.
To understand how the GAA trinucleotide expansion leads to FRDA, researchers looked at X25 gene expression by extracting RNA from affected and unaffected patients and doing a northern blot analysis (see the figure below):
- In panel “a,” the researchers used a probe to detect X25 mRNA.
- In panel “b,” the researchers used a probe on a duplicate of the original blot to detect human GAPDH mRNA (GAPDH is an enzyme involved in glycolysis).
The sample labeled “YR” is mRNA from yeast cells that was used as a control.
Explain exactly what the X25 probe is and how it allows for visualization of mRNA from the patients. Include in your answer why GAPDH was also analyzed.
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