レチノイン酸誘導された胚性幹細胞分化の間に活性化された予測と遺伝子調節要素の検証
Summary
In this work we provide an experimental workflow of how active enhancers can be identified and experimentally validated.
Abstract
胚発生は、多くの遺伝子の活性化と抑制を含む多段階プロセスです。ゲノム中のエンハンサーエレメントは、組織及び細胞分化の間の遺伝子発現の細胞型特異的調節に寄与することが知られています。したがって、それらの同定およびさらなる調査は、細胞の運命を決定する方法を理解するために重要です。遺伝子発現データ（ 例えば、マイクロアレイまたはRNA-seqの）およびクロマチン免疫沈降（ChIPの）ベースのゲノムワイドな研究（チップ配列）の結果の統合は、これらの調節領域の大規模な同定を可能にします。しかしながら、細胞型特異的エンハンサーの機能的検証は、in vitroおよびdi vivo実験手順でさらに必要とします。ここでは、アクティブなエンハンサーを同定し、実験的に検証できる方法について説明します。このプロトコルは、ステップバイステップのワークフローを提供します：1）のChIP-seqのデータ解析による調節領域の同定、2）クローニングおよびEXPERimentalレポーターアッセイで同定されたゲノム配列の推定調節の可能性の検証、およびエンハンサーRNA転写物のレベルを測定することにより、in vivoでのエンハンサー活性の3）決意。提示されたプロトコルは、ラボでは、このワークフローを設定するために誰を助けるために十分に詳述されています。重要なことに、このプロトコルは容易に適応し、任意の細胞モデル系において使用することができます。
Introduction
Development of a multicellular organism requires precisely regulated expression of thousands of genes across developing tissues. Regulation of gene expression is accomplished in large part by enhancers. Enhancers are short non-coding DNA elements that can be bound with transcription factors (TFs) and act from a distance to activate transcription of a target gene1. Enhancers are generally cis-acting and most frequently found just upstream of the transcription start site (TSS), but recent studies also described examples where enhancers were found much further upstream, on the 3′ of the gene or even within the introns and exons2.
There are hundreds of thousands of potential enhancers in the vertebrate genomes1. Recent methods based on chromatin immunoprecipitation (ChIP) provide high-throughput data of the whole genome that can be used for enhancer analysis3-9. Though data obtained by ChIP-seq experiments greatly increases the likelihood to identify cell and tissue-specific enhancers, it is important to keep in mind that detected binding sites do not necessarily identify direct DNA binding and/or functional enhancers. Thus, further functional analysis of newly identified enhancers is indispensable. In this work, we present a basic three-step process of putative active enhancer identification and validation. This includes: 1) selection of putative transcription factor binding sites by bioinformatics analysis of ChIP-seq data, 2) cloning and validation of these regulatory sequences in reporter constructs, and 3) measurement of enhancer RNA (eRNA).
Exposure of embryonic stem (ES) cells to retinoic acid (RA) is frequently used to promote neural differentiation of the pluripotent cells 10. RA exerts its effects by binding to RA receptors (RARα, β, γ) and retinoid X receptors (RXRα, β, γ). RARs and RXRs in a form of heterodimer bind to DNA motifs called RA-response elements, that is typically arranged as direct repeats of AGGTCA sequence (called as half site) and regulate transcription. Ligand-treatment experiments allowed the identification of several retinoic acid regulated genes in ES cells 11,12. However, enhancer elements for many of these genes has not been described yet. To demonstrate how the here-described workflow can be used for enhancer identification and validation we show step-by-step the selection and characterization of two retinoic acid-dependent enhancers in embryonic stem cells.
Protocol
Representative Results
Discussion
In recent years, advances in sequencing technology have allowed large-scale predictions of enhancers in many cell types and tissues 7-9. The workflow described above allows one to perform primary characterization of candidate enhancers chosen based on ChIP-seq data. The detailed steps and notes will help anyone to set up a routine enhancer validation in the lab.
The most critical step in the luciferase reporter assay is the transfection efficiency. It is recommended to include a GFP…
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
The authors would like to acknowledge Dr. Bence Daniel, Matt Peloquin, Dr. Endre Barta, Dr. Balint L Balint and members of the Nagy laboratory for discussions and comments on the manuscript. L.N is supported by grants from the Hungarian Scientific Research Fund (OTKA K100196 and K111941) and co-financed by the European Social Fund and the European Regional Development Fund and Hungarian Brain Research Program – Grant No. KTIA_13_NAP-A-I/9.
Materials
| KOD DNA polymerase | Merck Millipore | 71085-3 | for PCR amplification of enhancer from gDNA |
| DNeasy Blood & Tissue kit | Qiagen | 69504 | for genomic DNA isolation |
| QIAquick PCR Purification kit | Qiagen | 28106 | for PCR product purification |
| Gel extraction kit | Qiagen | 28706 | for gel extraction if there are more PCR product |
| HindIII | NEB | R3104L | restriction enzyme |
| BamHI | NEB | R3136L | restriction enzyme |
| FastAP | Thermo Scientific | EF0651 | release of 5'- and 3'-phosphate groups from DNA |
| T4 DNA ligase | NEB | M0202 | for ligation |
| QIAprep Spin Miniprep kit | Qiagen | 27106 | for plasmid isolation |
| DMEM | Gibco | 31966-021 | ES media |
| FBS | Hyclone | SH30070.03 | ES media |
| MEM Non-Essential Amino Acid | Sigma | M7145 | ES media |
| Penicillin-Streptomycin | Sigma | P4333 | ES media |
| Beta Mercaptoethanol | Sigma | M6250 | ES media |
| FuGENE HD | Promega | E2311 | transfection reagent |
| Opti-MEM® I Reduced Serum Medium | Life Technologies | 31985-062 | for transfection |
| All-trans retinoic acid | Sigma | R2625 | ligand, for activation of RAR/RXR |
| 96-well clear plate | Greiner | 655101 | for Beta galactosidase assay |
| 96-well white plate | Greiner | 655075 | for Luciferase assay |
| D-luciferin, potassium salt | Goldbio.com | 115144-35-9 | for Luciferase assay |
| ATP salt | Sigma | A7699-1G | for Luciferase assay |
| MgSO4x 7H2O | Sigma | 230391-25G | for Luciferase assay |
| HEPES | Sigma | H3375-25G | for Luciferase assay |
| Na2HPO4 x 7H2O | Sigma | 431478-50G | for Beta galactosidase assay |
| NaH2PO4 x H2O | Sigma | S9638-25G | for Beta galactosidase assay |
| MgSO4 x 7H2O | Sigma | 230391-25G | for Beta galactosidase assay |
| KCl | Sigma | P9541-500G | for Beta galactosidase assay |
| ONPG (o-nitrophenyl-β-D-galactosidase) | Sigma | N1127-1G | for Beta galactosidase assay |
| TRIzol® | Life Technologies | 15596-026 | RNA isolation |
| High-Capacity cDNA Reverse Transcription Kit | Life Technologies | 4368814 | reverse transcription of eRNA |
| Rnase-free Dnase | Promega | M6101 | Dnase treatment |
| SsoFast Eva Green | BioRad | 750000105 | RT-qPCR mastermix |
| CFX384 Touch™ Real-Time PCR Detection System | BioRad | qPCR machine | |
| BioTek Synergy 4 microplate reader | BioTek | luminescent counter |
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