BioProject

Purpose: We used Global run-on sequencing, a gold standard assay to measure transcriptional activity to examine the change of genome transcription in the absence of RAD21 subunit of cohesin, a critical chromatin architectural protein complex. More...

Purpose: We used Global run-on sequencing, a gold standard assay to measure transcriptional activity to examine the change of genome transcription in the absence of RAD21 subunit of cohesin, a critical chromatin architectural protein complex. In particularl, we tested how the loss of chromatin looping regulator cohesin would impact the enhancers and their target promoter transcription. Methods: Transfection of small interfering RNAs (siRNAs) into MCF-7 cells was performed using Lipofectamine 2000 (Life technologies) following manufacturer's instructions. For all experiments, two rounds of siRNA transfection (40nM each time) were performed to achieve higher efficiency. The siRNAs used in this study include: Qiagen Negative Control siRNA (Qiagen Cat# 1027310) and/or Sigma Mission siRNA universal control #2 (SIC002); siRAD21 (Sigma SASI_Hs02_00341219 and SASI_Hs01_00195799). The transfected MCF7 cells were subjected to GRO-seq experiments. GRO-Seq experiments were performed as previously reported (Li et al., 2013, Nature). Briefly, ~10-20 millions of MCF-7 cells were washed 3 times with cold PBS and then sequentially swelled in swelling buffer (10mM Tris-Cl pH7.5, 2mM MgCl2, 3mM CaCl2) for 5 min on ice, harvested, and lysed in lysis buffer (swelling buffer plus 0.5% NP-40 and 10% glycerol). The resultant nuclei were washed one more time with 10mL lysis buffer and finally re-suspended in 100uL of freezing buffer (50mM Tris-Cl pH8.3, 40% glycerol, 5mM MgCl2, 0.1mM EDTA). For the run-on assay, re-suspended nuclei were mixed with an equal volume of reaction buffer (10mM Tris-Cl pH 8.0, 5mM MgCl2, 1mM DTT, 300mM KCl, 20 units of SUPERase-IN, 1% sarkosyl, 500uM ATP, GTP, and Br-UTP, 2uM CTP) and incubated for 5 min at 30°C . The resultant nuclear-run-on RNA (NRO-RNA) was then extracted with TRIzol LS reagent (Life Technologies) following manufacturer’s instructions. NRO-RNA was fragmented to ~300-500nt by alkaline base hydrolysis on ice and followed by treatment with DNase I and Antarctic phosphatase. These fragmented Br-UTP labeled nascent RNA was then immunoprecipitated with an anti-BrdU argarose beads (Sc32323ac, Santa Cruz Biotechnology) in binding buffer (0.5XSSPE, 1mM EDTA, 0.05% tween) for 3 hrs at 4°C with rotation. Subsequently, T4 PNK was used to repair the end of the immunoprecipitated BrU-NRO-RNA, at 37°C for 1hr. The RNA was extracted and precipitated using acidic phenol-chloroform. cDNA synthesis was performed as per a published method (54) with few modifications. The RNA fragments were subjected to poly-A tailing reaction by poly-A polymerase (NEB) for 30 min at 37°C. Subsequently, reverse transcription was performed using oNTI223 primer and superscript III RT kit (Life Technologies). The cDNA products were separated on a 10% polyacrylamide TBE-urea gel and only those migrated between ~100-500bp were excised and recovered by gel extraction. After that, the first-strand cDNA was circularized by CircLigase (Epicentre) and re-linearized by APE1 (NEB). Re-linearized single strand cDNA (sscDNA) was separated by a 10% polyacrylamide TBE gel as described above and the product of needed size was excised (~170-400bp) for gel extraction. Finally, sscDNA template was amplified by PCR (usually between 10-14 PCR cycles) using the Phusion High-Fidelity enzyme (NEB) according to the manufacturer’s instructions. The resulted library was subjected to deep sequencing. Results: Using an optimized data analysis workflow, we generated three biological replicates of GRO-seq in the presence or absence of cohesin, and with or without treatment by estrogen. Overall design: Transfection of small interfering RNAs (siRNAs) into MCF-7 cells was performed using Lipofectamine 2000 (Life technologies) following manufacturer's instructions. For all experiments, two rounds of siRNA transfection (40nM each time) were performed to achieve higher efficiency. The siRNAs used in this study include: Qiagen Negative Control siRNA (Qiagen Cat# 1027310) and/or Sigma Mission siRNA universal control #2 (SIC002); siRAD21 (Sigma SASI_Hs02_00341219 and SASI_Hs01_00195799). The transfected MCF7 cells were subjected to GRO-seq experiments. GRO-Seq experiments were performed as previously reported (Li et al., 2013, Nature). Briefly, ~10-20 millions of MCF-7 cells were washed 3 times with cold PBS and then sequentially swelled in swelling buffer (10mM Tris-Cl pH7.5, 2mM MgCl2, 3mM CaCl2) for 5 min on ice, harvested, and lysed in lysis buffer (swelling buffer plus 0.5% NP-40 and 10% glycerol). The resultant nuclei were washed one more time with 10mL lysis buffer and finally re-suspended in 100uL of freezing buffer (50mM Tris-Cl pH8.3, 40% glycerol, 5mM MgCl2, 0.1mM EDTA). For the run-on assay, re-suspended nuclei were mixed with an equal volume of reaction buffer (10mM Tris-Cl pH 8.0, 5mM MgCl2, 1mM DTT, 300mM KCl, 20 units of SUPERase-IN, 1% sarkosyl, 500uM ATP, GTP, and Br-UTP, 2uM CTP) and incubated for 5 min at 30°C . The resultant nuclear-run-on RNA (NRO-RNA) was then extracted with TRIzol LS reagent (Life Technologies) following manufacturer’s instructions. NRO-RNA was fragmented to ~300-500nt by alkaline base hydrolysis on ice and followed by treatment with DNase I and Antarctic phosphatase. These fragmented Br-UTP labeled nascent RNA was then immunoprecipitated with an anti-BrdU argarose beads (Sc32323ac, Santa Cruz Biotechnology) in binding buffer (0.5XSSPE, 1mM EDTA, 0.05% tween) for 3 hrs at 4°C with rotation. Subsequently, T4 PNK was used to repair the end of the immunoprecipitated BrU-NRO-RNA, at 37°C for 1hr. The RNA was extracted and precipitated using acidic phenol-chloroform. cDNA synthesis was performed as per a published method (54) with few modifications. The RNA fragments were subjected to poly-A tailing reaction by poly-A polymerase (NEB) for 30 min at 37°C. Subsequently, reverse transcription was performed using oNTI223 primer and superscript III RT kit (Life Technologies). The cDNA products were separated on a 10% polyacrylamide TBE-urea gel and only those migrated between ~100-500bp were excised and recovered by gel extraction. After that, the first-strand cDNA was circularized by CircLigase (Epicentre) and re-linearized by APE1 (NEB). Re-linearized single strand cDNA (sscDNA) was separated by a 10% polyacrylamide TBE gel as described above and the product of needed size was excised (~170-400bp) for gel extraction. Finally, sscDNA template was amplified by PCR (usually between 10-14 PCR cycles) using the Phusion High-Fidelity enzyme (NEB) according to the manufacturer’s instructions. The resulted library was subjected to deep sequencing. Less...