Selection of appropriate reference genes for normalization of qRT-PCR based gene expression analysis in SARS-CoV-2, and Covid-associated Mucormycosis infection

Selection of reference genes in quantitative PCR is critical to determine accurate and reliable mRNA expression. Despite this knowledge, not a single study has investigated the expression stability of housekeeping genes to determine their suitability to act as reference gene in SARS-CoV-2 or Covid19 associated mucormycosis (CAM) infections. Herein, we address these gaps by investigating the expression stability of nine most commonly used housekeeping genes including TBP, CypA, B2M, 18S, PGC-1, GUSB, HPRT-1, {beta}-ACTIN and GAPDH in the patients of varying severity (asymptomatic, mild, moderate and severe). We observed significant differences in the expression of candidate genes across the disease spectrum. Next, using various statistical algorithms (delta Ct, Normfinder, Bestkeeper, RefFinder and GeNorm), we observed that CypA demonstrated the most consistent expression across the patients of varying severity and emerged as the most suitable gene in Covid19, and CAM infections. Incidentally, the most commonly used reference gene GAPDH showed maximum variations and found to be the least suitable. Lastly, comparative evaluation of expression of NRF2 is performed following normalization with GAPDH and CypA to highlight the relevance of an appropriate reference gene. Our results reinforce the idea of a selection of housekeeping genes only after validation especially during infections.