Interpreting Tissue-Specific Western Blot Results

A researcher has obtained an antibody to cytosolic protein X and runs a Western blot using as samples a variety of tissue types. The results of the Western blot are shown below. A potential interpretation of the results is which of the following?

A. Codon degeneracy within the genetic code
B. Tissue-specific posttranslational modifications
C. Tissue-specific alternative splicing of the primary transcript
D. Polyadenylation is lacking in certain tissues

Interpreting Western Blot Results: Understanding Tissue-Specific Variations in Protein X

Correct Answer: (C) Tissue-Specific Alternative Splicing of the Primary Transcript

A Western blot is used to detect specific proteins in different biological samples based on their molecular weight and expression levels. In this experiment, the researcher analyzed cytosolic protein X across various tissue types, observing different banding patterns. This suggests that Protein X exhibits tissue-specific variations.

Possible Explanations for the Observed Western Blot Results

1. Codon Degeneracy (Option A) – Incorrect

   • Codon degeneracy refers to the redundancy of the genetic code, where multiple codons encode the same amino acid.
   • This does not affect protein size or alter Western blot results, as it only impacts mRNA translation without modifying the final protein product.

2. Tissue-Specific Posttranslational Modifications (Option B) – Partially Possible

   • Posttranslational modifications (PTMs) like phosphorylation, glycosylation, or ubiquitination can slightly alter protein migration in SDS-PAGE.
   • However, these modifications typically cause minor shifts in band size, not the significant size variations expected from splicing.

3. Tissue-Specific Alternative Splicing (Option C) – Correct Answer

   • Alternative splicing allows a single gene to produce multiple protein isoforms by including or excluding exons in different tissues.
   • If alternative splicing occurs, Protein X may have different molecular weights in various tissues, leading to multiple bands in the Western blot.
   • This perfectly explains the observed banding pattern, where some tissues show larger or smaller isoforms of Protein X.

4. Lack of Polyadenylation in Certain Tissues (Option D) – Incorrect

   • Polyadenylation affects mRNA stability and translation efficiency, but it does not change the size of the translated protein.
   • A lack of polyadenylation would more likely reduce protein expression rather than alter its molecular weight on a Western blot.

Conclusion

The presence of multiple bands for Protein X across tissues strongly suggests that alternative splicing generates distinct isoforms of the protein, leading to size differences. Therefore, the correct interpretation is (C) Tissue-Specific Alternative Splicing of the Primary Transcript.