DNA and RNA references for qRT-PCR assays in exfoliated cervical cells

The noncritical use of housekeeping genes, RNA mass, or cell number for normalization in quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) assays has come under scrutiny in recent years, highlighting the need to evaluate references in the immediate context of the relevant samples and experimental design. The purpose of this study was to select appropriate references for normalizing qRT-PCR assays of gene expression in exfoliated cervical cells. We used total nucleic acid extracts from 30 samples, representing the full spectrum of pre-invasive cervical neoplasia. We determined the DNA content by quantitative PCR for the single-copy gene beta-globin and total RNA content using quantitative image analysis of ribosomal bands. In addition, qRT-PCR for 13 candidate housekeeping genes was performed. We used two analysis methods, geNorm and Norm-Finder, to identify the best combination of reference genes and then correlated housekeeping gene expression with DNA content and gel representation of ribosomal RNA. ACTB was the most stable single gene. The addition of PGK1 and RPLP0 increased the robustness in qRT-PCR applications not stratified by disease. These genes also showed the highest correlation with DNA contents in the same samples. If special attention to intraepithelial lesions is appropriate, RPL4 and PGK1 are recommended as the best combination of two genes.