Changes in biomolecular profile in a single nucleolus during cell fixation

Area of Science:

• Cell biology
• Biophysics
• Spectroscopy

Background:

• Biological sample fixation is crucial for preserving molecular content but can alter cellular structures.
• Understanding fixation-induced changes is vital for accurate biomolecular analysis.
• Raman spectroscopy offers sensitive molecular characterization.

Purpose of the Study:

• To quantitatively assess the impact of formaldehyde and ethanol fixation on nucleolar biomolecular composition using Raman spectroscopy.
• To compare the effects of different fixation methods on protein and RNA concentrations and structures.
• To guide the selection of appropriate fixation protocols for specific molecular studies.

Main Methods:

• Quantitative Raman spectroscopy was used to analyze nucleoli in HeLa cells before and after fixation.
• Cells were fixed using either formaldehyde solution or chilled ethanol.
• Coherent anti-Stokes Raman scattering (CARS) nonlinear optical imaging was employed for protein and lipid mapping.

Main Results:

• Formaldehyde fixation showed minimal spectral changes but could decrease RNA concentration.
• Ethanol fixation increased protein and RNA concentrations by up to 40%, likely due to shrinkage.
• Ethanol fixation altered protein conformation, reducing alpha-helical and increasing beta-sheet structures.

Conclusions:

• Formaldehyde fixation is suitable for in situ protein mapping due to minimal structural alteration.
• Ethanol fixation is advantageous for studying RNA-containing macromolecules, despite inducing protein conformational changes.
• Fixation method choice significantly impacts biomolecular composition and structure, necessitating careful consideration for experimental design.