You are working to characterize a novel protein in mice. Characterization of the mRNA expression pattern revealed that the gene is highly expressed in brain, muscle, liver, and pancreas. To determine the size of the corresponding protein, you make protein extracts from each of the tissues. Using an antibody that recognizes the C-terminal portion of the protein, you perform an analysis that allows you to visualize the extracted protein. Interestingly, you can detect the protein in brain, muscle, and liver, but not the pancreas. Assuming your extracts and reagents are good, and there is no human error, what is the most likely explanation for this result?