miRNAs in Normal Human Tissues
miRNA from 26 normal human tissues was purified. A pool of one half of each sample was placed in a tube. The miRNAs from the pooled sample as well as each of the 26 single-tissue samples were fluorescently labeled with Cy3 or Cy5 using the mirVana miRNA Labeling Kit. Each tissue-specific miRNA sample was mixed with part of a pooled sample and the mixtures were hybridized to miRNA arrays generated from the mirVana miRNA Probe Set. The relative signal intensities of the single and pooled samples were compared for each miRNA. Each of the 26 normal human tissues that were analyzed had a unique pattern of miRNA expression. Hierarchical clustering shows that miRNA profiles are similar between related tissues and distinct between unrelated tissues--heart and skeletal muscle profiles are very similar, digestive tract tissues cluster, and reproductive organ tissues are similar (Figure 4). Interestingly, the brain miRNA profile is clearly distinct from the other tissues that were analyzed. Approximately 30 miRNAs are expressed primarily in 1-3 related tissue types. Interestingly, many of the putative target genes for these miRNAs associate with the same tissue wherein the miRNAs are expressed (data not shown).
Figure 4. Relative miRNA Expression inNormal Human Tissues. The miRNA expression profiles (y axis) of 26 different human normal tissues (x axis) was compared to a pool of all 26 samples. Green in the heat map shows miRNAs t