一种多标签单分子定位显微镜协议，用于在高密度核环境中研究染色质
2026年6月5日
我们提出了一种三色染色质单分子定位显微镜（SMLM）染色与分析方案，能够对常染色质、异染色质和RNAP II进行空间分析的可重复定位。该协议能够在密集核环境中高效进行多色标记，包括染色质相关靶点，实现可靠的同时检测。
我们的研究探讨染色质填积结构域的表观遗传组成，以及调控因子如何塑造其结构和功能。该协议最适合研究靶点与密集细胞环境（如细胞核）之间的空间关系。首先，称重牛血清白蛋白，使实验所需缓冲液的最终浓度为3%。将牛血清白蛋白加入离心管。
将离心管倾斜至45度角，将牛血清白蛋白晶体扩散开来，然后向管内添加PBS。这防止了晶体结团。让所有牛血清白蛋白晶体在室温下自然溶解，避免震动或旋转。
晶体完全溶解后，加入Triton X-100，达到最终浓度0.2%。如果仍有晶体，则用移液器上下移液数次，缓慢混合且不形成气泡。从孵育箱里取活细胞。将细胞培养基从盘中取出。
通过添加足够的PBS覆盖细胞清洗细胞，然后用移液器取出PBS。接着，移液液量足以覆盖细胞，静置10分钟。使用天平称重硼氢化钠，制备0.1%淬火溶液。
将硼氢化钠加入离心管中。从洗碗中取出定弦液。然后，在盘中加入足够的PBS，覆盖细胞表面。
将盘子放在摇罐上清洗五分钟。接着，将所需体积的PBS加入离心管中的硼氢化钠。用漩涡冲压管子来混合淬火液。
将盘子从摇罐中取出，并丢弃PBS的容器。加入足够的淬火溶液，覆盖整个盘面。然后将盘子放在摇罐上，浸泡七分钟，以抑制细胞中的自发荧光。
将离心管内剩余的淬火溶液丢弃到标有相应标签的液体化学废弃物容器中。把盘子从摇床里取出，然后把淬火溶液从盘子里取出。然后，往盘子里加入足够的PBS，覆盖整个表面。
将盘子放在摇罐上清洗五分钟。孵育后，取出PBS，并用PBS重复两次洗涤。现在，给盘子加足够的阻挡缓冲剂覆盖表面。
将盘子在摇床上孵育至少一小时，以渗透细胞膜并阻断结合位点。准备初级抗体染色溶液时，将所需体积的阻断缓冲液转移到新的离心管中。将所需的初级抗体库存加入阻断缓冲液中，以达到制造商指定的最终浓度。
接着，用足够的初级抗体染色液替换阻断缓冲液，覆盖盘面，并在摇床上孵育一到两小时或一夜。初级抗体培养后，用洗涤缓冲液替换原版抗体溶液。然后，将盘子放在摇罐上清洗细胞五分钟。
重复洗涤缓冲液两次，总共三次。根据推荐浓度准备二级抗体染色液。通过在覆盖细胞所需的体积上增加0.5毫升，计算出总染色溶液体积。
将缓冲液中计算出的体积转移到新的离心管中，以制备染色溶液。然后，将适当量的二级抗体样本加入阻断缓冲液中，以获得正确的最终浓度。用铝箔包裹装有二级抗体染色溶液的离心管，然后上下移液混合溶液。
在盘子中加入足够的二级抗体染色液，覆盖表面。将天线放在摇杯上40分钟，将荧光团附着在标记的细胞靶上。用铝箔纸覆盖天盘以防止荧光团漂白。
40分钟后，按照之前演示进行两次PBS洗涤。如果偏好储存，储存前向盘内添加足够的PBS覆盖细胞表面。用防腐剂包裹盘子以防止液体蒸发，然后用铝箔纸包裹以防止荧光团漂白。
将包裹好的盘子保存在四摄氏度，直到准备成像。序列染色协议产生了多细胞系（包括BJ成纤维细胞、HeLa和MCF 10A细胞）的代表性三色dSTORM染色质图像。分析流程使用模拟数据集评估，这些数据集代表了正常、均匀的环向和随机空间分布，锚定在异染色质簇的位置上。
当分析相对于异染色质质心的定位坐标时，不同的空间组织模式产生了特征性的距离直方图轮廓。在正常脉丝带结构中模拟空间分离标记产生最小的关节密度，形成平坦分布轮廓。在正常随机配置下模拟重叠标记图案，随着距离参考点的增加，连接密度逐渐降低。
基于数据库扫描的异染色质结构域识别使得基于有效半径的区域可分为小域、中域和大域。定量距离分析显示，RNA聚合酶II和H3K27ac在小、中、大区域的异染色质边界附近定位。关节密度分析显示H3K27ac和RNA聚合酶II共定位峰值位于异染色质簇边界外。
利用该方案，研究人员可以探究染色质看似无序的组织结构，探讨其结构、调控元件与功能结果之间的关系。在此程序之后，各种基于图像或点云的计算分析可以根据所用成像方式，从空间数据中提取定量结构特征。研究人员可以通过优化更多标记和利用多通道数据来扩展这种标记方法，从而实现更高级和全面的分析。
Overview
This article presents a sequential immunolabeling protocol for robust three-color single molecule localization microscopy (SMLM) in dense nuclear environments, enabling high-fidelity imaging of chromatin components. The method includes optimized buffer formulations, fluorophore selection, and antibody validation strategies to minimize crosstalk and signal degradation. It is integrated with a computational analysis pipeline that uses localizations from one target as spatial anchors to quantify inter-target distances, local densities, and multi-label co-affinity. The protocol is demonstrated in BJ Fibroblast, HeLa, and MCF 10A cells and supports detailed nanoscale spatial analysis of chromatin architecture.
Key Study Components
Area of Science
- Cell Biology
- Microscopy
- Chromatin Biology
Background
- Chromatin exhibits multiscale organization from nucleosomes to micron-scale domains, requiring high-resolution and specific imaging approaches.
- Single molecule localization microscopy (SMLM), particularly STORM, enables nanoscale mapping of epigenetic marks.
- Multi-label imaging in the nucleus faces challenges such as reduced antibody accessibility, non-specific binding, and fluorophore instability.
- Existing protocols often lack robustness in dense subcellular environments like the nucleus.
Purpose of Study
- To develop a sequential immunolabeling protocol optimized for high-density nuclear environments.
- To enable robust three-color SMLM with minimal crosstalk and reduced signal degradation.
- To integrate the protocol with a computational pipeline for quantitative spatial analysis of chromatin components.
- To provide a reproducible framework for multi-component imaging in dense subcellular environments.
Methods Used
- Sequential immunolabeling with optimized buffer formulations and fluorophore selection.
- Blocking with 3% BSA, fixation, and quenching with 0.1% sodium borohydride to reduce autofluorescence.
- Primary and secondary antibody incubations with washing steps to minimize non-specific binding.
- dSTORM imaging under buffered conditions to stabilize fluorophores.
- Computational analysis using localizations from one target as seed points to measure inter-target distances and joint densities.
- DB scan-based clustering to categorize heterochromatin domains by effective radius.
Main Results
- The protocol produced representative three-color dSTORM images in BJ Fibroblast, HeLa, and MCF 10A cell lines.
- Simulated data showed distinct distance histogram profiles based on spatial organization of markers relative to heterochromatin centroids.
- RNA polymerase II and H3K27ac were localized near heterochromatin boundaries across small, medium, and large domains.
- Joint density analysis revealed peak colocalization of H3K27ac and RNA polymerase II just outside heterochromatin cluster boundaries.
- The analysis pipeline enabled quantification of structural features from spatial point cloud data derived from SMLM.
Conclusions
- The sequential immunolabeling protocol enables reliable, high-fidelity three-color SMLM in dense nuclear environments.
- Integration with computational analysis allows nanoscale quantification of chromatin spatial organization.
- The method provides a reproducible framework for studying spatial relationships between chromatin components and regulatory factors.
- Researchers can extend the approach by optimizing additional markers for comprehensive multi-target analysis.
- This protocol advances the investigation of chromatin structure-function relationships in native cellular contexts.
Frequently Asked Questions
Executive Industry Relevance
This protocol addresses a critical bottleneck in chromatin research: achieving robust, multiplexed super-resolution imaging in the dense nuclear environment where antibody accessibility and signal stability are major limitations. By enabling quantitative nanoscale mapping of epigenetic marks and regulatory factors relative to heterochromatin domains, it provides a mechanistic de-risking tool for target validation in epigenetic drug discovery. The integrated computational pipeline transforms raw localization data into actionable spatial metrics, supporting predictive confidence in early-stage target hypothesis testing.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of spatial relationships between chromatin marks, transcription factors, and heterochromatin to clarify mechanistic hypotheses in epigenetic regulation.
- Operational Value: Provides a standardized, reproducible framework for multiplexed target co-localization studies in dense subcellular environments.
- Predictive Value: Quantifies nanoscale proximity and co-affinity between targets, supporting target prioritization based on spatial context and functional relevance.
Screening & Assay Development
- Assay Readiness: Generates validated, high-fidelity three-color SMLM data suitable for assay standardization and reproducibility assessment in nuclear target engagement studies.
- Scalability: Supports extension to additional markers via sequential labeling, enabling scalable multi-parameter chromatin architecture profiling.
- Analytical Output: Produces quantifiable spatial features such as inter-target distances, local densities, and joint density profiles for downstream screening hit validation.
Translational & Preclinical Research
- Disease Relevance: Facilitates study of chromatin organization in disease-relevant cell models, linking epigenetic target modulation to structural outcomes.
- Translational Continuity: Bridges discovery-phase spatial insights with preclinical validation by providing consistent, quantifiable nuclear imaging readouts.
- Risk-Adjusted Advancement: Enables mechanistic de-risking of epigenetic targets through direct visualization of their nanoscale chromatin environment and regulatory neighbors.
Pipeline & Workflow Integration
The method fits within the discovery continuum from target hypothesis generation through lead identification, where spatial chromatin context informs target druggability and mechanism of action. It enables screening-ready assay development by delivering standardized, multiplexed nuclear imaging data with quantitative outputs. The computational pipeline provides analytics-ready spatial metrics that support cross-functional comparison of compound or genetic perturbations on chromatin architecture.
- Discovery Biology: Supports hypothesis testing and pathway clarification by mapping epigenetic marks and regulatory factors relative to heterochromatin domains.
- Screening: Delivers assay-ready, reproducible three-color SMLM data with minimized crosstalk for reliable compound effect assessment in nuclear targets.
- Analytics: Generates inter-target distance measurements, local density maps, and joint density profiles from localization data to quantify spatial relationships.
- Translational Research: Connects nanoscale chromatin organization findings to preclinical continuity through standardized, quantifiable spatial readouts.
- Enterprise Reuse: Establishes a reusable, standardized protocol for multi-target nuclear imaging applicable across chromatin-focused discovery programs.
Operational & Enterprise Impact
- Scientific Value: Reduces mechanistic ambiguity in epigenetic target validation through direct nanoscale spatial mapping of chromatin components and regulators.
- Operational Value: Ensures standardization, reproducibility, and signal fidelity in multiplexed nuclear SMLM via optimized blocking, antibody validation, and buffer formulations.
- Strategic Value: Improves go/no-go decisions in epigenetic target programs by providing spatial context that predicts functional target engagement and pathway modulation.
- Portfolio Impact: Enables risk-adjusted prioritization of epigenetic targets based on validated chromatin localization and co-affinity with key regulatory elements.
Implementation Considerations
- Requires expertise in super-resolution microscopy, immunostaining, and point cloud analysis for accurate data interpretation.
- Dependent on SMLM-capable instrumentation and stable fluorophore selection compatible with sequential labeling and buffering conditions.
- Necessitates cross-team standardization of antibody validation, blocking efficiency, and quenching protocols to minimize batch variability.
- Involves adaptation considerations for different chromatin targets, including epitope accessibility and antibody penetration in fixed dense nuclei.
- Limited by the sequential nature of staining, which increases total protocol time and requires careful optimization to avoid target loss or signal degradation over multiple rounds.
