Preparing Lamellae from Vitreous Biological Samples Using a Dual-Beam Scanning Electron Microscope for Cryo-Electron Tomography
August 5th, 2021
5.5K views
Using focused ion beam milling to produce vitreous on-grid lamellae from plunge frozen biological samples for cryo-electron tomography.
Overview
This protocol details the preparation of cryo-lamellae from plunge-frozen grids of Plasmodium falciparum-infected human erythrocytes for cryo-electron microscopy (cryoEM) and cryo-electron tomography (cryoET). The method enables high-resolution structural analysis of malaria parasites within red blood cells and can be adapted for other biological samples. The workflow emphasizes careful sample preparation, focused ion beam milling, and transfer to transmission electron microscopy under cryogenic conditions.
Key Study Components
Area of Science
- Structural biology
- Cell biology
- Electron microscopy
- Parasitology
Background
- Cryo-electron tomography allows visualization of cellular structures at high resolution in near-native states.
- Preparation of thin, vitreous lamellae is essential for imaging thick biological samples such as infected erythrocytes.
- Plasmodium falciparum is the causative agent of malaria, and understanding its cellular architecture is critical for malaria research.
- Optimized lamella preparation improves reproducibility and data quality for downstream analyses.
Purpose of Study
- To provide a robust protocol for preparing cryo-lamellae from malaria-infected red blood cells.
- To enable direct observation of parasite-induced cellular changes using cryoET.
- To facilitate adaptation of the protocol for other cell types and biological samples.
Methods Used
- Plunge-freezing of electron microscopy grids containing infected erythrocytes.
- Screening grids using a cryo-stage light microscope to assess ice thickness and cell distribution.
- Sputter coating or e-beam rotary coating with carbon/platinum for charge dispersal and protection.
- Focused ion beam-scanning electron microscopy (cryoFIB-SEM) for stepwise milling and organoplatinum coating via gas injection system.
- Sequential reduction of ion beam current to achieve electron-transparent lamellae (~300 nm thick).
- Polishing lamellae at low current and monitoring by SEM.
- Transfer of prepared lamellae to cryo-TEM for tilt-series acquisition and structural analysis.
Main Results
- Efficient production of thin, high-quality lamellae suitable for cryoET imaging.
- Visualization of P. falciparum schizonts and merozoites within red blood cells at various stages of egress.
- Identification of key ultrastructural features, including parasitophorous vacuole membranes, hemozoin crystals, and organelles such as micronemes and rhoptries.
- Observation of membrane fusion events and detailed parasite morphology in situ.
Conclusions
- The described protocol enables reproducible preparation of cryo-lamellae for high-resolution structural studies of malaria parasites.
- Optimization of grid preparation and milling parameters is critical for successful lamella production.
- This workflow supports advanced cryoEM and cryoET studies, facilitating insights into parasite biology and host-pathogen interactions.
Frequently Asked Questions
What is the main advantage of using cryo-lamellae for studying malaria-infected erythrocytes?
Cryo-lamellae allow high-resolution, in situ visualization of parasite and host cell structures in a near-native, vitrified state, enabling detailed structural analysis by cryo-electron tomography.
How is sample thickness controlled during lamella preparation?
Sample thickness is controlled by stepwise milling with a focused ion beam, gradually reducing the current as the lamella approaches electron transparency, typically reaching a final thickness of about 300 nanometers.
Why are grids coated with carbon or platinum before milling?
Coating with carbon or platinum disperses charge buildup during milling and protects the sample surface, improving the quality and integrity of the lamellae.
What features of P. falciparum can be visualized using this protocol?
The protocol enables visualization of schizonts, merozoites, parasitophorous vacuole membranes, hemozoin crystals, and organelles such as micronemes, rhoptries, and the inner membrane complex.
Can this protocol be adapted for other biological samples?
Yes, the protocol is broadly applicable and can be adapted for preparing cryo-lamellae from various cell types and biological specimens for cryoEM and cryoET studies.
What are critical steps for ensuring high-quality lamellae?
Careful screening of grids for ice thickness and cell distribution, precise coating, controlled milling, and gentle handling under cryogenic conditions are essential for producing high-quality lamellae.
What downstream applications are enabled by this workflow?
Prepared lamellae can be used for cellular cryoEM, cryoET, and sub-tomogram averaging to study protein complexes and cellular architecture in situ.
Executive Industry Relevance
Robust preparation of cryo-lamellae from vitrified biological samples is pivotal for enabling high-resolution structural analysis in early discovery and target validation workflows. This protocol supports direct visualization of cellular architecture and protein complexes in situ, enhancing predictive confidence and mechanistic de-risking for disease-relevant systems. Reliable lamella production underpins downstream cryo-electron tomography, facilitating translational continuity from discovery through preclinical research.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables direct interrogation of cellular ultrastructure and protein localization within disease-relevant models.
- Supports mechanistic de-risking by revealing native-state interactions and subcellular organization.
- Improves predictive confidence for target validation by providing high-resolution, context-specific data.
Screening & Assay Development
- Facilitates preparation of standardized, reproducible lamellae for consistent downstream imaging workflows.
- Enables quantitative assessment of sample integrity and morphology prior to high-content screening.
- Supports scalability and platform reuse across diverse biological samples and experimental conditions.
Translational & Preclinical Research
- Aligns structural insights with disease models, supporting translational biomarker identification.
- Ensures continuity from discovery-stage imaging to preclinical validation of molecular mechanisms.
- Reduces biological risk by providing direct evidence of target engagement and cellular effects.
Pipeline & Workflow Integration
This lamella preparation protocol integrates at the interface of discovery biology and advanced imaging, bridging early mechanistic studies with preclinical structural validation.
- Discovery Biology: Supports hypothesis testing and pathway clarification through direct visualization of cellular events.
- Screening: Delivers reproducible, electron-transparent lamellae for quantitative imaging and comparative analysis.
- Analytics: Provides high-resolution structural readouts to inform condition selection and mechanistic interpretation.
- Translational Research: Enables alignment of imaging outputs with disease-relevant phenotypes and biomarker strategies.
- Enterprise Reuse: Establishes a standardized workflow adaptable to multiple cell types and research programs.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence and reduces mechanistic ambiguity in target validation.
- Operational Value: Promotes standardization, reproducibility, and scalability in sample preparation and imaging.
- Strategic Value: Informs go/no-go decisions and enhances capital efficiency by reducing late-stage biological risk.
- Portfolio Impact: Supports risk-adjusted prioritization and advancement of structurally validated targets.
Implementation Considerations
- Requires expertise in cryo-electron microscopy and focused ion beam milling.
- Demands access to cryoFIB-SEM, TEM, and cryogenic sample handling infrastructure.
- Necessitates rigorous cross-team standardization for reproducible lamella quality.
- Adaptable across various biological models with protocol optimization for sample-specific needs.
- Dependent on careful grid screening and contamination control for optimal outcomes.
Biopharma FAQs
Why does null hypothesis testing matter for lamella-based target validation?
Null hypothesis testing using cryo-lamellae enables objective assessment of structural differences between experimental conditions, supporting rigorous validation of target engagement and mechanistic hypotheses in situ.
How does independent variable isolation fit the lamella preparation workflow?
Isolating variables such as coating thickness, milling current, and sample orientation ensures that observed structural outcomes are attributable to biological differences rather than technical artifacts, strengthening discovery-stage conclusions.
What do quantitative dependent variable measurements enable in cryo-lamella analysis?
Quantitative measurements of lamella thickness, cell morphology, and ultrastructural features provide reproducible benchmarks for comparing experimental groups and optimizing imaging conditions across studies.
Why are replication requirements critical for cross-functional lamella workflows?
Replication ensures that lamella preparation and imaging outputs are consistent across operators and instruments, enabling reliable data integration and cross-team collaboration in multi-site R&D environments.
What statistical analysis capabilities are required before implementing lamella-based imaging?
Robust statistical tools are needed to analyze structural data, assess reproducibility, and compare conditions, ensuring that imaging-derived insights meet enterprise standards for decision-making and portfolio advancement.
