Cross-reaction of miRNA precursors with miRNA probes. (A) Array analysis for mouse spinal cord and mouse brain using 60–200 nt small RNAs. Some miRNA (miR-690, miR-709, and miR-720) precursors of over 60 nt cross-reacted with miRNA probes (, cf. A and B). (B) Northern blotting analysis of pre-miR-690, pre-miR-709, and pre-miR-720, which are highly abundant and cross-react with the probes of their mature miRNAs, and pre-miR-124a, pre-miR-122a, and pre-miR-133a, which are very little or none and have no cross-reaction with the probes of their mature miRNAs. Signals from pre-miRNAs are highlighted by arrows. (Lanes 1,2,3,4) Samples from spinal cord, brain, liver, and heart, respectively.