Expression of shRNA vs. miRNA

 List of expression vectors and prices

For gene silencing purpose, shRNA and miRNA are functionally interchangeable. The choice of mRNA cleavage or translational repression determined solely by the degree of complementarity between the small RNA and its target. Most commercial RNAi expression vectors use mammalian Pol III promoters, e.g. U6 or H1, for shRNA expression, while use Pol II promoters, e.g. CMV, for miRNA expression. Such discrimination has caused confusion and difficulty among some users.

Studies have shown that cellular miRNA genes are transcribed by RNA polymerase II. However, the initial transcripts, i.e. pri-miRNAs, which are usually over one kilo-bases in length, have to be processed into pre-miRNA (~70 nt) and active miRNA (21 – 23 nt), which are similar to shRNA (~50 nt) and siRNA (21 – 22 nt) in size, respectively (Figure 1).

Figure 1

After intensive tests, we offer users free options to subclone shRNA or miRNA hairpins into the same RNAi expression vector from RNAi Combination Toolbox™ solely based on your research needs (Figure 2).

Figure 2

Notably, these vectors are specially designed so that it is possible to express both shRNA and miRNA at same time by generating multiple expression cassettes on a single vector.

For those who prefer to use Pol II promoters to express miRNAs, you still can find that some vectors, which carry CMV or SV40 early promoters for general/rescue cDNA expression purposes, will meet your needs.