Figure 1: TERRA and telomere transcription in ALT cells.

(a) TERRA northern blot hybridizations of RNA from the indicated cell lines (VA13: WI-38 VA13; 1.2.11: HeLa 1.2.11) pre-treated with RNaseA or left untreated. Ethidium bromide stained 18S ribosomal RNA (rRNA) is shown to control for loading. Long TERRA molecules comprised between the wells of the gels (w) and 28S rRNA are indicated. (b) TERRA CpG-island promoter methylation analysis of the indicated cell lines. Genomic DNA was digested with the methylation sensitive restriction enzyme MspI or its methylation insensitive isoschizomer HpaII. DNA was hybridized using a radioactively labelled probe detecting TERRA promoter CpG-island repeats. Nomet: fragments corresponding to unmethylated restriction products. (c) Dot blot hybridization of DNA immunoprecipitated with antibodies against phosphorylated Serines S2 and S5 of RNA polymerase II C-terminal domain. Hybridizations were performed with a telomeric probe. Quantifications are shown at the bottom. (d) Bars and error bars are averages and s.d. from three independent experiments. (e) Examples of TERRA FISH in the indicated cells. TERRA is shown in red, DAPI-stained DNA in blue. Scale bar, 9 μm. (f) IF/FISH experiments in the indicated cell lines. TERRA is in red, TRF2 in green and PML in blue. In the merge panels, arrowheads point to nuclear foci where the three factors co-localize. Scale bar, 9 μm. (g) Information surface at 0.01 μm detail level of three TERRA-containing APBs. TERRA is in red, TRF2 in green and PML in cyan. Images were generated with Three-Dimensional Structured Illumination Microscopy (3D-SIM). Scale bars, 0.4 μm.