Oct 19, 2022
Preparation of tissue for transmission electron microscopy ultrastructural analysis
- Jillian C Danne1,
- Simon A Crawford1,
- Rachel Templin1,
- Joan Clark1,
- Viola Oorschot2,
- Georg Ramm1
- 1Ramaciotti Centre for Cryo EM, Monash University, Melbourne, Australia;
- 2Electron Microscopy Core Facility, EMBL, Heidelberg, Germany
Protocol Citation: Jillian C Danne, Simon A Crawford, Rachel Templin, Joan Clark, Viola Oorschot, Georg Ramm 2022. Preparation of tissue for transmission electron microscopy ultrastructural analysis. protocols.io https://dx.doi.org/10.17504/protocols.io.n92ldpz9nl5b/v1
License: This is an open access protocol distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Protocol status: Working
We use this protocol and it's working
Created: October 18, 2022
Last Modified: October 19, 2022
Protocol Integer ID: 71511
Keywords: Transmission electron microscopy, Tissue, Epon resin, Ultrastructure, Processing, Contrasting, Ultramicrotomy, Embedding, Dehydration
Abstract
A transmission electron microscope (TEM) enables the magnification and visualisation of cell and tissue ultrastructure that cannot otherwise be resolved using a light microscope. In transmission electron microscopy, a high energy electron beam generated from an electron gun is focused by electromagnetic lenses onto an ultrathin section of plastic embedded specimen. Electrons are transmitted through the specimen onto a fluorescent screen based on sample density, and an image is acquired by a digital camera. Here, a protocol for preparing tissue specimens for TEM ultrastructural analysis is described. A tissue specimen is fixed, dehydrated and infiltrated with resin. The resin is then polymerised, and embedded tissue sectioned using an ultramicrotome. Ultrathin sections are contrasted with heavy metals prior to imaging using a TEM. Options for faster processing using a Microwave processor are described for relevant steps.
Materials
Paraformaldehyde, 16% (wt/vol)Electron Microscopy SciencesCatalog #15710
Glutaraldehyde 25% Aqueous Solution 10 x 10 ml ampoulesElectron Microscopy SciencesCatalog #16220
Sodium Cacodylate Trihydrate 100gProSciTechCatalog #C020
0.2M Sodium Cacodylate Trihydrate Buffer pH 7.4Contributed by users
0.1M Sodium Cacodylate Trihydrate Buffer pH 7.4Contributed by users
Osmium tetroxide 10 x 1g ampouleProSciTechCatalog #C010-1010
Potassium hexacyanoferrate(II) trihydrateSigma AldrichCatalog #P3289-100G
Ethanol Absolute AR grade 2.5LAIM ScientificCatalog #AJA214-2.5L
MilliQ waterContributed by users
30% Ethanol in MilliQ waterContributed by users
50% Ethanol in MilliQ waterContributed by users
70% Ethanol in MilliQ waterContributed by users
90% Ethanol in MilliQ waterContributed by users
95% Ethanol in MilliQ waterContributed by users
Molecular sieves 3 ÅSigma AldrichCatalog #208574-1KG
Epon resinContributed by users
Toluidine blue Merck Millipore Sigma
Uranyl acetateElectron Microscopy SciencesCatalog #22400
Lead (II) citrate tribasic trihydrateSigma AldrichCatalog #15326-25g
10M sodium hydroxide solutionMerck Millipore SigmaCatalog #72068
Equipment
Black teflon plate
NAME
N/A
BRAND
N/A
SKU
Equipment
Fine Forceps
NAME
Forceps
TYPE
Dumont
BRAND
11251-10
SKU
LINK
Equipment
Bite and boxing wax-500g
NAME
Investo (Lordell)
BRAND
WI-BB
SKU
Equipment
Blade scalpel ST #11
NAME
Swann Morton
BRAND
21016SM
SKU
Equipment
Single edge carbon steel blade
NAME
Electron Microscopy Sciences
BRAND
71960
SKU
Equipment
Tube 5ml 5016 PP yellow cap GS
NAME
Pacific Laboratory Products
BRAND
P5016SU
SKU
Equipment
Falcon® Centrifuge Tubes
NAME
Polypropylene, Sterile, 15 mL
TYPE
Corning®
BRAND
352096
SKU
Equipment
Rotary tube mixer
NAME
Ratek Instruments
BRAND
RSM7DC
SKU
Equipment
PELCO BioWave® Pro+ Microwave Processing System, 120VAC
NAME
Pelco
BRAND
36700
SKU
Equipment
Embedding mould, single ended flat 21 cavities
NAME
ProSciTech
BRAND
RL064
SKU
Equipment
Flat bottom embedding capsules, microwave safe
NAME
BEEM®
BRAND
70021-PPT
SKU
Equipment
BEEM® embedding capsules, size OO, PE, Pack/500
NAME
BEEM®
BRAND
RB001-500
SKU
Equipment
3ml graduated transfer pipette
NAME
Copan
BRAND
200C
SKU
Equipment
Gilson pipetman classic P1000
NAME
Gilson
BRAND
1152009
SKU
Equipment
Oven MINO/6/CLAD
NAME
Genlab
BRAND
N/A
SKU
Equipment
Olympus SZ30 stereo microscope
NAME
Olympus
BRAND
SZ30-PS
SKU
Equipment
UC7 Ultramicrotome
NAME
Leica
BRAND
EMUC7
SKU
Equipment
Double edge blades
NAME
Personna
BRAND
72000
SKU
Equipment
Glass knife, 45 degree
NAME
Leica
BRAND
N/A
SKU
Equipment
Glass knife boat, 6.4mm
NAME
Electron microscopy sciences
BRAND
71008
SKU
Equipment
Ultra Semi diamond knife, 35 degree angle, 3 mm
NAME
Diatome
BRAND
UltraSemi
SKU
Equipment
Eyelash or Dalmatian hair mounted on a wooden stick
NAME
N/A
BRAND
N/A
SKU
Equipment
Plain glass slides 76mm x 39mm x 1.0-1.2mm
NAME
Thermo Scientific
BRAND
AGL4222A
SKU
Equipment
Mini hot plate
NAME
Thermofisher
BRAND
HP2310BQ
SKU
Equipment
Olympus widefield microscope, model CHK2-F-GS
NAME
Olympus
BRAND
N/A
SKU
Equipment
Ultra wet diamond knife, 45 degree angle, 3mm
NAME
Diatome
BRAND
UU45-30
SKU
Equipment
Heat pen for ultramicrotomy
NAME
Max Wax
BRAND
U060
SKU
Equipment
50 Mesh palladium/copper grids
NAME
Gilder
BRAND
GCU-PD50
SKU
Equipment
50 Mesh copper grids
NAME
Gilder
BRAND
GCU50
SKU
Equipment
200 Mesh copper grids
NAME
Gilder
BRAND
GCU200
SKU
Equipment
200 Mesh palladium/copper grids
NAME
Gilder
BRAND
GCU-PD200
SKU
Equipment
Glass petri dish, 100mm
NAME
BRAND
BRAND
BR455751
SKU
Equipment
Grid storage box, 100 grid capacity
NAME
Gilder
BRAND
HL065
SKU
Equipment
Parafilm M
NAME
Bemis
BRAND
IA041
SKU
Equipment
Glass board
NAME
N/A
BRAND
N/A
SKU
Equipment
Perfect loop
NAME
Diatome
BRAND
70944
SKU
Equipment
10ml Syringe, Luer lock tip
NAME
Terumo
BRAND
19046TE
SKU
Equipment
Acrodisc syringe filter 25mm, 0.2um pore size
NAME
Pall Corporation
BRAND
Z259969
SKU
Equipment
Foil
NAME
N/A
BRAND
N/A
SKU
Equipment
Filter paper, grade 1, 12.5cm
NAME
Whatman
BRAND
1001-125
SKU
Equipment
JEOL JEM-1400 Plus 120keV Transmission electron microscope
NAME
JEOL
BRAND
N/A
SKU
Safety warnings
The following chemicals must be handled with extreme care in a fume hood using the appropriate personal protective equipment (PPE):
Paraformaldehyde and glutaraldehyde are toxic, corrosive and potentially carcinogenic.
Cacodylate buffer contains arsenic, and is acutely toxic and carcinogenic.
Osmium tetroxide is extremely toxic. Used osmium should be discarded in a labelled plastic container containing ethanol to reduce and neutralise the osmium.
Potassium ferrocyanide is acutely toxic.
Uranyl acetate is mildly radioactive and extremely toxic if ingested, inhaled or in contact with abraded or cut skin.
Fixation
Fixation
All fixation and processing steps must be performed in a fume hood wearing appropriate personal protective equipment (PPE). The Material Safety Data Sheet (MSDS) for each chemical must be read before commencing.
Dissect out the tissue of interest on a Teflon plate or dental wax sheet using fine forceps and a scalpel blade at room temperature, and keeping the tissue submerged in Karnovsky's fixative, 2% paraformaldehyde, 2.5% glutaraldehyde in 0.1M cacodylate buffer (pH 7.2). Tissue pieces should be no larger than 1 mm cubed to ensure sufficient infiltration of fixative, solvents and resin.
Place the tissue pieces in 5 ml tubes, 15 ml Falcon® tubes or a well-plate containing 2% paraformaldehyde, 2.5% glutaraldehyde in 0.1M cacodylate buffer and fix overnight at 4 degrees Celsius or for 2-4 hours at room temperature, on a rotor.
Wash with 0.1M cacodylate buffer, 3 x 10 minutes at room temperature, agitating.
Osmium tetroxide is extremely toxic and must be handled with care in a fume hood using the appropriate PPE. Used osmium should be discarded in a labelled plastic container containing ethanol to reduce and neutralise the osmium.
Osmium can precipitate out of solution when in the presence of glutaraldehyde to form small electron dense artefactual deposits. Samples must be washed thoroughly (Step 3) prior to post-fixation (Step 4) to avoid this.
Potassium ferrocyanide reduces osmium, turning the post fixation solution black. Reduced osmium may also prevent the formation of artefactual precipitates. Potassium ferricyanide can be used as an alternative in combination with osmium tetroxide. This solution is a clear, amber colour.
The following steps can be performed with or without the use of a PELCO BioWave® Pro+ Microwave Processing System. A Biowave facilitates infiltration of reagents into tissue and cells, and reduces the processing time.
Post fix the tissue in 1% Osmium tetroxide, 1.5% potassium ferrocyanide in 0.1M cacodylate buffer for 2 hours at room temperature, agitating. Tube or well-plate lids must be well-secured during fixation.
Biowave settings: 3x 120 seconds, 100W, Vacuum on.
A two minute pause step without a solution change must be included in between each interval to prevent overheating of samples.
Wash in MilliQ water, 3 x 10 minutes at room temperature, agitating.
Washed samples can be stored at 4 degrees Celsius for up to 1 week until further processing.
Dehydration and resin infiltration
Dehydration and resin infiltration
For Steps 6-19, do not proceed if samples float following ethanol, acetone or Epon resin infiltration.
Well-infiltrated samples should sink in solution. If they do not, samples may require extended infiltration times.
Epon resin can be stored in the freezer but must come to room temperature before use.
Dehydrate in 30% ethanol in MilliQ water for 1 hour at room temperature, agitating.
Biowave settings: 40 seconds, 150W, No vacuum.
Dehydrate in 50% ethanol in MilliQ water for 1 hour at room temperature, agitating.
Biowave settings: 40 seconds, 150W, No vacuum.
Dehydrate in 70% ethanol in MilliQ water for 1 hour at room temperature, agitating. Tissue can be left at 4 degrees Celsius, overnight if necessary.
Biowave settings: 40 seconds, 150W, No vacuum.
Dehydrate in 90% ethanol in MilliQ water for 1 hour at room temperature, agitating.
Biowave settings: 40 seconds, 150W, No vacuum.
Dehydrate in 95% ethanol in MilliQ water for 1 hour at room temperature, agitating.
Biowave settings: 40 seconds, 150W, No vacuum.
Dehydrate in 100% ethanol for 1 hour at room temperature, agitating.
Biowave settings: 40 seconds, 150W, No vacuum.
Dehydrate in 100% anhydrous ethanol for 1 hour at room temperature, agitating. Type 3Å molecular sieves can be added to the ethanol stock solution to dehydrate the solvent prior to use.
Biowave settings: 40 seconds, 150W, No vacuum.
Dehydrate in 100% acetone for 1 hour at room temperature, agitating.
Biowave settings: 40 seconds, 150W, No vacuum.
Propylene oxide can be used as an alternative to acetone (Steps 13-17), but is extremely toxic and may dehydrate samples too intensively, causing ultrastructural damage.
Dehydrate in 100% anhydrous acetone for 1 hour at room temperature, agitating. Type 3Å molecular sieves can be added to the acetone stock solution to dehydrate the solvent prior to use.
Biowave settings: 40 seconds, 150W, No vacuum.
Optionally Infiltrate with 100% anhydrous acetone : epon resin (3 : 1 ratio) overnight at room temperature, agitating.
Biowave settings: 3 minutes, 250W, Vacuum on.
Infiltrate with 100% anhydrous acetone : epon resin (1 : 1 ratio) for 6 hours at room temperature, agitating.
Biowave settings: 3 minutes, 250W, Vacuum on.
Infiltrate with 100% anhydrous acetone : epon resin (1 : 3 ratio) overnight at room temperature, agitating.
Biowave settings: 3 minutes, 250W, Vacuum on.
Infiltrate with 100% epon resin for 6 hours at room temperature, agitating.
Biowave settings: 3 minutes, 250W, Vacuum on.
Infiltrate with 100% epon resin overnight at room temperature, agitating.
Biowave settings: 3 minutes, 250W, Vacuum on.
Residual acetone can adversely impact resin infiltration and polymerisation. A third 100% resin infiltration step may be required to prevent this.
Transfer samples to labelled plastic embedding moulds, flat bottom BEEM® capsules or standard tip BEEM® capsules containing 100% epon resin. Polymerise in an oven set to 60 degrees Celsius for 24-48 hours.
Semi and ultrathin sectioning
Semi and ultrathin sectioning
Mount the resin-embedded tissue block in an ultramicrotome chuck, and secure the chuck to a stereo microscope fitted with a chuck mount. Manually trim the front face and all four edges of the tissue block into a trapezoid shape using a double edge razor blade.
Transfer the chuck and resin-embedded tissue block to a Leica UC7 ultramicrotome and secure in place. Trim the front surface of the block face until a full tissue face has been obtained. Trim manually using an 0.5 μm feed and a 45 degree glass knife (thickness 6.4 mm or 8 mm) or suitable diamond knife, for example a Diatome 35 degree angle ultra semi diamond knife.
To check the region of interest:
Cut 500 nm semi thin sections at a speed of 1 mm/sec using a Leica UC7 ultramicrotome and 45 degree glass knife fitted with a filtered water-filled boat or suitable diamond knife.
Retrieve sections with an eyelash or Dalmatian hair mounted on a wooden stick and float sections in a drop of MilliQ water on a slide before drying on a mini hot plate.
Stain sections with Toluidine blue solution for 10-20 seconds on a mini hot plate before rinsing with MilliQ water and drying on a mini hot plate.
Toluidine blue stains nucleic acids and proteins, enhancing structural detail of semi thin tissue sections.
Observe sections with a wide-field light microscope. If the region of interest has not been obtained, trim deeper and repeat Step 23.
Cut 90 nm gold coloured ultrathin sections at 1 mm/sec using a Leica UC7 ultramicrotome and a Diatome 45 degree angle ultra wet diamond knife. Spread the sections using a Max Wax heat pen to remove wrinkles.
Pick up sections on 50-200 mesh copper or palladium-coated copper grids using an eyelash or Dalmatian hair mounted on a wooden stick. Place grids section side up on a sheet of filter paper, cover with a glass petri dish and leave to dry for 10 minutes. Store grids in an enclosed grid box until use.
Contrasting ultrathin sections
Contrasting ultrathin sections
Place a sheet of parafilm on a clean flat bench or glass board using a small amount of water underneath to keep the film flat.
For the following steps, use fine forceps or a perfect loop to transfer grids from one drop of solution to another, section side down. Use approximately 100-200 μl drops for MilliQ water, and 50-100 μl for uranyl acetate and lead citrate.
Stain sections with 0.6% filtered uranyl acetate in MilliQ water for 3 minutes.
Uranyl acetate enhances contrast of sections by interacting with proteins and lipids. The solution must be wrapped in foil and stored in a dark place to prevent precipitation from exposure to UV light.
Rinse 5 x 1 min in MilliQ water.
Stain sections with 0.1-0.4% filtered lead citrate in MilliQ water for 3 minutes.
Four drops of 10M sodium hydroxide should be added to the lead citrate stock solution prior to use to prevent lead citrate precipitating to form water-insoluble lead carbonate by exposure to carbon dioxide.
Lead citrate enhances contrast of sections by interacting with proteins and glycogens, and binding to osmium and uranyl acetate.
Rinse 5 x 1 min in MilliQ water.
Place grids section side up on a sheet of filter paper, cover with a glass petri dish and dry for 10 minutes. Store grids in a grid storage box.
Place a grid in a transmission electron microscope grid holder for high resolution imaging using a transmission electron microscope.
Example: JEOL JEM-1400-Plus TEM at 80 keV equipped with a high sensitivity bottom mount CMOS 'Flash' camera.