How to choose reverse transcriptase for RT qPCR of low copy genes?

For exosomal miRNA and low-copy mRNA from tens of ng of total RNA, prioritize reverse transcription master mixes explicitly stated to be suitable for low-input or single-cell-level RNA input. These products typically contain RNase inhibitors, and their buffers are optimized for small 10 μL reaction volumes. Focus on whether the instructions state that stable reverse transcription can be achieved from 10 ng or even less total RNA, and require the manufacturer to provide validation data for low-copy genes.

It is recommended to use stem loop primers or tail specific reverse transcription primers for miRNA, as regular random hexamers may not provide sufficient coverage for short miRNAs; MRNA can be mixed with oligo dT to improve cDNA integrity and uniformity. It is recommended to denature the RNA at 65 ℃ for 5 minutes before reverse transcription using the high GC template, and then quickly immerse it in an ice bath before entering the system. This step is particularly important for low initial sample sizes.

For a 10 μL system, the sample volume is small; low-binding microcentrifuge tubes and filter tips are recommended to reduce loss from tube wall adsorption. Exogenous RNase inhibitors are not a substitute for operational precautions—consumables and bench surfaces must be RNase-free. If Ct values remain high after switching enzymes, first confirm RNA integrity and concentration accuracy; otherwise, simply increasing enzyme amount or switching enzymes may not resolve the issue.

After obtaining the candidate enzyme, perform gradient dilution with the same batch of RNA, such as 50ng, 10ng, and 2ng, and compare the Ct values linearly with the reverse transcription efficiency. For high GC templates, betaine or DMSO can be added, but a template free control should be performed simultaneously to avoid an increase in primer dimers. When the price is acceptable, priority should be given to brands that can provide small package trials, have technical support, and assist in optimizing low copy solutions.