Reference gene selection for real-time qPCR in European flounder (Platichthys flesus) using organ-specific RNA-seq data.

Background: The European flounder is readily chosen as an experimental subject and model in physiological and ecotoxicological studies mostly because of its adaptability to laboratory conditions. Many studies utilise a quantitative PCR (qPCR) approach to ascertain the expression of target genes under experimental conditions. Such an approach relies heavily on the selection of reference genes with stable expression. Yet certain housekeeping genes are commonly used in this role, often without due consideration of their overall expression patterns. Therefore, new approaches should be developed to identify stable reference genes for a given species and to expand the general pool of genes suitable for the reference in qPCR analysis.

Methods and results: Here RNA-seq data of nine flounder organs led to identify four candidate genes of the most stable expression. It was achieved by differential expression analysis and tritoconstrictor script. Specific primers were designed for the complete ORF as well as for qPCR analysis. RT-qPCR efficiencies were tested on ORF amplicon templates. Most of the genes tested showed good amplification in a wide range of template dilutions (10⁷-10¹), with a correlation coefficient (R²) ranging from 0.991 to 0.998 and a consistent efficiency (E) (Sybr Green I staining and TaqMan molecular probe).

Conclusions: The proposed approach based on differential expression analysis and a new bioinformatic tool is an appropriate selection method of candidates for reference genes in qPCR. The proposed approach, combining differential expression analysis with a new bioinformatics tool, provides an effective method for selecting reference gene candidates for qPCR. As a result, we can propose four genes (polr2f, yif1a, sf3b6, uba52), each with a set of validated primers, as suitable for consideration as reference genes in qPCR analysis in European flounder, an emerging model species.