An Evolutionary Perspective of Animal MicroRNAs and Their Targets
Figure 2
Genomic organization of miRNA genes and their expression. The number of miRNA genes correlates with chromosome length (a) and the number of protein-coding genes (b). Outliers chromosomes 14, 19, and are indicated. When removing these three chromosomes the number of miRNA genes aligns well on the regression line ( indicated). (c) Proportion of miRNA genes hosted in Introns—Intronic (based on Refseq genes), Clustered on the same genomic strand, or Stand-alone miRNAs. Overlapping intronic and clustered miRNAs are also indicated. Each row refers to 50 kb, 10 kb, and 1 kb distance between paired genes on the same strand. It was shown that clusters of size 3 kb give a large proportion of clusters (27%) with little change when increasing pairwise distance to 10 kb [54]. Diagrams are based on data from Refseq. (d) Human miRNA copy number was plotted against the average miRNA expression level of 40 Human tissues [60]. A similar plot of another dataset [55] gave comparable results (data not shown).
