Table 1.
The miRNA Classification Schemea
| Acronym | Meaning | Examples |
|---|---|---|
| 3-Letter prefix | Species identification | hsa (Homo sapiens) |
| cel (Caenorhabditis elegans) | ||
| pri-mir (lower case “r”) | The primary miRNA transcript (see Figure 1) | pri-mir-1 |
| pre-mir (lower case “r”) | The precursor miRNA transcript resulting from processing of the primary transcript by the Drosha-DGCR8 complex (See Figure 1) | pre-mir-1 |
| miR (upper case “R”) | Mature miRNA | hsa-miR-1 |
| -3p or -5p | Mature miRNA originating from the 3′ or 5′ end of the pre-miRNA, respectively | hsa-miR-10-3p |
| hsa-miR-10-5p | ||
| a or b | Related, mature miRNA variants (i.e., differing by a nucleotide) | hsa-let 7a |
| hsa-let 7b | ||
| -1, or -2 | Identical mature miRNA sequences that originate from different genomic loci | hsa-miR-9-1 |
| hsa-miR-9-2 | ||
| miR* (miR-star) | “Passenger strand”b found at lower concentration, frequently degraded (retired after miRBase 16) | hsa-miR-9* |
| miR, miRNA, microRNA | Equivalent terms for a mature miRNA transcript used in the text of studies |
Abbreviation: miRNA, microRNA.
a Adapted from Pritchard et al. (38).
b The “*” (star) is appended to some miRNA names (e.g., miR-9*), especially in data sets generated using older miRNA profiling platforms. The designation of “*” is meant to indicate the “minor species” of the 2 mature miRNAs that are produced from the 3′ and 5′ arms of the pre-miRNA duplex (i.e., forming the miRNA:miRNA* duplex; Figure 1). It is now recognized that both the dominant (nonstar) and “star” forms can be functional (133) and, in some cases, may be present at comparable concentrations in the cell, or that the miRNA* form might even be at higher concentration depending on the precursor gene examined and the cell, tissue, or species (134) being examined. For these reasons, it is recommended that the miRNA/miRNA* nomenclature be dropped in favor of using the “-3p” or “-5p” suffix in every case.