Development and application of multiple internal reference (housekeeper) gene assays for accurate normalisation of canine gene expression studies.

Measurement of mRNA expression by real-time RT-PCR (QRT-PCR) has proven to be an important and powerful tool for the investigation of the pathogenesis of inflammatory and immune-mediated diseases in many species. This methodology has proven particularly valuable in the dog, a species for which there are currently few specific antibodies for measurement of relevant proteins. Internal control (housekeeper) mRNAs are widely used for normalisation of QRT-PCR results. The validation and use of multiple internal control mRNAs for increased accuracy of normalisation has been described for humans and rodents. The aims of this study were to develop QRT-PCR assays for 11 potential internal control mRNAs in the dog (ACTB, B(2)M, G3PDH, HMBS, HPRT1, RPL13A, RPL32, RPS18, SDHA, TBP and YWAZ) and validate their use with bone marrow, colon, duodenum, heart, kidney, liver, lung, lymph node, skeletal muscle, pancreas, spleen and stomach from seven dogs. Endoscopic biopsies of the superficial duodenal mucosa were also obtained from nine dogs suffering from chronic gastro-oesophageal disease. The most stably expressed genes varied in the tissues examined. RPL13A and RPL32 (both components of the 60S ribosomal subunit) were the most stably expressed genes in the majority of the tissues examined, whereas ACTB and B(2)M were the least stable. Distinct internal control genes were shown to be most appropriate for use in full-thickness versus superficial mucosal biopsies of the duodenum. The results of this study indicate that there are no universal control genes for gene expression studies in canine tissues. It is important to use multiple internal control genes based upon a survey of potential control genes applied to representative samples from different disease groups, culture conditions and/or time points in an experimental study.