Journal: J Struct Biol / Year: 2021 Title: VHUT-cryo-FIB, a method to fabricate frozen hydrated lamellae from tissue specimens for in situ cryo-electron tomography. Authors: Jianguo Zhang / Danyang Zhang / Lei Sun / Gang Ji / Xiaojun Huang / Tongxin Niu / Jiashu Xu / Chengying Ma / Yun Zhu / Ning Gao / Wei Xu / Fei Sun / Abstract: Cryo-electron tomography (cryo-ET) provides a promising approach to study intact structures of macromolecules in situ, but the efficient preparation of high-quality cryosections represents a ...Cryo-electron tomography (cryo-ET) provides a promising approach to study intact structures of macromolecules in situ, but the efficient preparation of high-quality cryosections represents a bottleneck. Although cryo-focused ion beam (cryo-FIB) milling has emerged for large and flat cryo-lamella preparation, its application to tissue specimens remains challenging. Here, we report an integrated workflow, VHUT-cryo-FIB, for efficiently preparing frozen hydrated tissue lamella that can be readily used in subsequent cryo-ET studies. The workflow includes vibratome slicing, high-pressure freezing, ultramicrotome cryo-trimming and cryo-FIB milling. Two strategies were developed for loading cryo-lamella via a side-entry cryo-holder or an FEI AutoGrid. The workflow was validated by using various tissue specimens, including rat skeletal muscle, rat liver and spinach leaf specimens, and in situ structures of ribosomes were obtained at nanometer resolution from the spinach and liver samples.
Name: Spinach 80S ribosome / type: complex / ID: 1 / Parent: 0 Details: Ribosomes were found in cryo-lamella of spinach leaf tissue.
Source (natural)
Organism: Spinacia olerac (spinach)
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Experimental details
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Structure determination
Method
cryo EM
Processing
subtomogram averaging
Aggregation state
particle
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Sample preparation
Buffer
pH: 7
Vitrification
Cryogen name: NITROGEN
Details
A puncher was used to cut a slice at about 2 mm diameter from the leaf of spinach. The leaf was then put in the recess of the carrier and frozen by HPF. A lamella was milled from the frozen sample through FIB. Tilt series data was collected on the lamella.
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Electron microscopy
Microscope
FEI TITAN KRIOS
Image recording
Film or detector model: GATAN K2 SUMMIT (4k x 4k) / Detector mode: COUNTING / Digitization - Dimensions - Width: 3838 pixel / Digitization - Dimensions - Height: 3710 pixel / Digitization - Frames/image: 1-20 / Number grids imaged: 1 / Average exposure time: 1.0 sec. / Average electron dose: 3.0 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Electron optics
Illumination mode: FLOOD BEAM / Imaging mode: BRIGHT FIELD
Applied symmetry - Point group: C1 (asymmetric) / Algorithm: FOURIER SPACE / Resolution.type: BY AUTHOR / Resolution: 34.0 Å / Resolution method: FSC 0.143 CUT-OFF / Software - Name: RELION (ver. 1.4) / Number subtomograms used: 923
Extraction
Number tomograms: 3 / Number images used: 1341 / Software: (Name: IMOD (ver. 4.9.2), RELION (ver. 1.4)) Details: Particles were manually picked from reconstructed tomogram.
CTF correction
Software - Name: CTFFIND (ver. 4)
Final angle assignment
Type: MAXIMUM LIKELIHOOD / Software - Name: RELION (ver. 1.4)
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