Why was it proposed that in the proximal small intestine (duodenum and jejunum) ASBT mRNA is present but protein is not?

• A. Possibly because gene expression techniques (ISH) are more sensitive
• B. The mRNA may not be undergoing translation in the proximal segments
• C. Protein is rapidly degraded in the proximal segments
• D. ASBT is not expressed in proximal segments at all

Answer: (A)

The main idea is that mRNA and protein can be detected with different sensitivities, leading to apparent discordance. In situ hybridization can reveal even low levels of ASBT mRNA in the proximal small intestine, whereas the corresponding protein may be present at very low abundance or be degraded or not trafficked to the brush border, making it undetectable by standard protein assays. So, ASBT transcripts can be detected by a sensitive mRNA technique in the duodenum and jejunum, while the protein remains below the detection threshold or is not efficiently translated or stabilized there. While translational control or rapid protein turnover could also explain it, the most straightforward and general explanation is that ISH is more sensitive for detecting low-abundance transcripts than protein assays.