Malat1 ncRNA is a stable nuclear RNA that localizes to speckles in a transcription-dependent manner. (A) RNA-FISH to untreated wt-MEFs shows the nuclear speckle localization of Malat1 ncRNA. (B) α-amanitin treatment (50 μg/ml for 6 h) of wt-MEFs results in the re-distribution of Malat1 ncRNA from nuclear speckles to a homogenous nuclear distribution. (C) Malat1 ncRNA levels in untreated and α-amanitin-treated (6, 12 and 18 h) wt-MEFs were assessed by Q–PCR. Malat1 ncRNA showed little to no turnover, similar to the RNA pol III-transcribed ncRNA 7SK. As expected, the protein coding mCAT2 mRNA showed high turnover after α-amanitin treatment. Malat1, mCAT2 and 7SK RNA levels were normalized to β-actin mRNA and were presented relative to RNA levels in untreated (control) cells. The data represents mean and s.d. values of three independent experiments per data point. (D–G) RNA-FISH to wt-MEFs (untreated cells) shows complete co-localization of Malat1 ncRNA with a nuclear speckle marker SF2/ASF. (H–K) Malat1 ncRNA shows homogenous nuclear distribution upon inhibition of RNA pol II transcription by DRB (32 μg/ml for 3 h) and it no longer co-localizes with SF2/ASF. (L–O) Following the removal of DRB from the medium (15 min), Malat1 ncRNA continues to show a homogenous distribution, whereas SF2/ASF relocalizes to nuclear speckles. (P–S) Malat1 ncRNA relocalizes to nuclear speckles within 30 min post-washout of DRB from the medium. RNA-FISH is shown in red (D, H, L, P), YFP-SF2/ASF in green (E, I, M, Q) and DNA is counterstained with DAPI in blue (G, K, O, S). Scale bar, 5 μm.