To accurately quantify mRNA and protein levels, it is critical to choose appropriate internal standards. As the expression of housekeeping genes is assumed to remain constant, they are often employed to normalize signals to correct for sample-to-sample variations. However, recent studies have documented that β-actin and Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) expression levels change in response to various stimuli during proliferation, activation, and differentiation. We investigated levels of α-, β-, γ-tubulin, β-actin, and GAPDH vary across the gastrointestinal tract of mice. We found that different regions of the small intestines had dramatically different expression profiles, as measured by western blot, quantitative Reverse transcription polymerase chain reaction (RT-PCR), and immunohistochemical staining. These results revealed that the expression levels of tubulins and β-actin were dramatically lower in the proximal duodenum, relative to the rest of the small intestines. These varying levels of housekeeping genes may reflect differences in the activities of specialized tissues and suggest unique requirements for tubulins in these tissue types. We conclude that the use of a single housekeeping gene to normalize gene expression in the gastrointestinal tracts of mice may introduce errors, as measured differences in gene expression may reflect regulation of the internal control rather than the mRNA or protein under investigation.
Bibliographical noteFunding Information:
This study was supported by faculty research grant from Yonsei University College of Medicine for 2013 (6-2013-0061), a new faculty research seed money grant from Yonsei University College of Medicine for 2013 (2013-32-0031), the Korea Mouse Phenotyping Center, and the Brain Korea 21 PLUS Project for Medical Science, Yonsei University, the Bio and Medical Technology Development Program of the National Research Foundation (NRF) funded by the Ministry of Science, ICT and Future Planning (NRF-2013M3A9D5072551), and Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2014R1A1A2058389) to K.T.N.
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