Figure 2. Inter-species comparisons to interrogate the diversity of miRNA families across species, lineage and/or kingdoms.

Summary of the miRBase R19 database comprising of 193 species and 1,543 miRNA families. The row-wise totals in blue show the number of species-specific miRNA genes in the 24 miRNA families analyzed in the figure. Totals under the “FAM” and “ALL” column labels are the number of miRNA genes in other miRNA families that were not selected for analysis and the total (family-annotated and non-family-annotated) number of registered miRNA genes in a given species, respectively. There are 1,600 registered human (Homo sapiens) among which 61.2% (229 plus 750) have been classified into different miRNA families. All the miRNA families mir-515, mir-548 and mir-663 genes have only been reported in primates, and similarly the most miRNA family mir-466 genes have been observed in mice (Mus musculus). A majority (>90%) of genes in the mir-467 family are mouse-specific. The disproportionate magnitude of homologous miRNA genes reflects the bias of most computational and experimental methods to favor miRNA annotation in certain species.