Housekeeping genes as internal standards: use and limits

Quantitative studies are commonly realised in the biomedical research to co mpare RNA expression in different experimental or clinical conditions. Thes e quantifications are performed through their comparison to the expression of the housekeeping gene transcripts like glyceraldehyde-3-phosphate dehydr ogenase (G3PDH), albumin, actins, tubulins, cyclophilin, hypoxantine phosph oribosyltransferase (HRPT), L32. 28S and 18S rRNAs are also used as interna l standards. In this paper, it is recalled that the commonly used internal standards can quantitatively vary in response to various factors. Possible variations are illustrated using three experimental examples. Preferred typ es of internal standards are then proposed for each of these samples and th ereafter the general procedure concerning the choice of an internal standar d and the way to manage its used are discussed. (C) 1999 Elsevier Science B .V. All rights reserved.