Digital quantitation of potential therapeutic target RNAs

Accurate determination of the amount of a given RNA within a cell is necessary to gain a full understanding of the RNA's function and regulation. Typically, the abundance of RNA is measured by quantitative polymerase chain reaction (qPCR). With qPCR, however, absolute quantification is not possible unless an adequate reference standard curve is generated. The method is not well suited for detecting low copy number templates and values vary depending on the specific primers used. To overcome these drawbacks, digital PCR (dPCR) has been developed to obtain exact values for RNA copies in a sample. Here we report the characterization of droplet digital PCR (ddPCR). We used ddPCR to quantify long noncoding RNAs from various subcellular compartments within human cells and found that results obtained using ddPCR parallel those from qPCR. Mutant huntingtin (HTT) protein is the cause of Huntington's Disease, and we show that we can quantify human HTT messenger RNA and discriminate between the mutant and wild-type HTT alleles using ddPCR. These results reveal insights into the design of experiments using ddPCR and show that ddPCR can be a robust tool for identifying the number of RNA species inside of cells.