In dogs with CIE, ileal ASBT protein expression is decreased, yet mRNA levels do not differ. What are two potential explanations for this discrepancy?

• A. Post-transcriptional modifications of the mRNA; Protein loss resulting from epithelial injury
• B. Increased transcription leading to more mRNA but less protein
• C. mRNA stability increased; Increased translation efficiency
• D. Sample contamination; Random variation

Answer: (A)

When a protein is reduced but its mRNA level stays the same, it points to regulation after transcription or to changes in the tissue makeup rather than changes in transcription itself. The ileal ASBT protein can be diminished even with unchanged mRNA because translation efficiency or mRNA usage can be altered after transcription. Post-transcriptional modifications—such as RNA-binding proteins or microRNAs that suppress translation, or changes in mRNA localization and stability—can reduce how much protein is made from the same amount of mRNA.

Another plausible factor is loss of the cells that normally express the protein. If epithelial injury or mucosal damage reduces the number of enterocytes bearing ASBT, the overall protein level detected in the tissue falls even though the remaining cells still have the same mRNA levels. This epithelial loss changes the tissue’s protein abundance without altering mRNA transcription.

These explanations fit the observed discrepancy better than scenarios requiring increased transcription or altered mRNA stability that would actually change mRNA levels, or random contamination, which wouldn’t provide a coherent biological mechanism.