Reference genes identified in the silkworm Bombyx mori during metamorphism based on oligonucleotide microarray and confirmed by qRT-PCR

Gene expression quantification at mRNA level is very important for post-genomic studies, as gene expression level is the reflection of the special biological function of the target gene. Methods used for gene expression quantification, such as microarray or quantitative real-time polymerase chain reaction (qRT-PCR), require stable expressed reference genes. Thus, finding suitable control genes is essential for gene quantification. In this study, a genome-wide survey of reference genes during metamorphism was performed on silkworm Bombyx mori. Twelve genes were chosen as putative reference genes based on a whole genome oligonucleotide microarray normalized by external controls. Then, qRT-PCR was employed for further validation and selection of potential reference gene candidates. The results were analyzed, and stable genes were selected using geNorm 3.4 and NormFinder software. Finally, considering factors from every aspect, translation initiation factor 4A, translation initiation factor 3 subunit 4, and translation initiation factor 3 subunit 5 (represented by sw22934, sw14876, and sw13956) were selected as reliable internal controls across the examined developmental stages, while cytoplasmic actin (sw22671), the commonly used reference gene in a previous study was shown to vary drastically throughout the examined developmental stages. For future research, we recommend the use of the geometric mean of those three stable reference genes as an accurate normalization factor for data normalization of different developmental stages during metamorphism.