Expression of new miRNAs in different tissues. RT-PCR analysis (+, with reverse transcriptase; -, without reverse transcriptase) of newly miRNAs in brain (B), liver (L), muscle (M) and mammary gland (MG) during lactation (day-10, L10) and involution (day-3, I03) were presented for 6 miRNAs. C samples without cDNA. ma: DNA marker. It is the 1-kb ladder from Gibco-BRL and it is shown using two different UV-light intensities to allow its better visualization.