Genomic organization and correlated expression of clustered miRNAs. (a) In some miRNA clusters, all members of the cluster can be expressed in a highly correlated pattern; (b,c) for other clusters, the expression of different cluster members can vary in level or pattern. In some cases, entire clusters, or individual cluster members, have been cloned in human or mouse cDNA libraries, or detected by northern blot hybridization (dotted lines). Some miRNAs are associated with aberrant cytological locations (parenthesis). Chromosomal location of miRNAs is given by their cytological coordinates or BAC clone. Expression profiles are shown for mouse and human brain (B), liver (Li), heart (H), skeletal muscle (M), lung (Lu), kidney (K), and spleen (S).