# Cryogenic electron tomography by the numbers: Charting underexplored lineages in structural cell biology

## TL;DR

This paper analyzes cryo-ET data from hundreds of cells to identify trends and underexplored species, aiming to improve imaging methods and expand biological insights.

## Contribution

The study consolidates cryo-ET data across life domains to reveal methodological trends and underrepresented lineages.

## Key findings

- Eukaryotes have 1% lamella coverage compared to 9% in bacteria and 14% in archaea.
- Serial lift-out is identified as a powerful sectioning method for multicellular imaging.
- Cryo-ET biodiversity is 2-5 orders of magnitude lower than predicted species diversity.

## Abstract

Cryogenic electron tomography (cryo-ET) is a powerful method for imaging inside cells, but it is challenging and typically limited to a few cells per study. We consolidate and quantify data from hundreds of cellular cryo-ET studies across the biosphere. The methodological trends we identify will heighten biological insight from underexplored lineages of life on Earth.

Imaging cells and their interactions across the whole biosphere with molecular-scale resolution is key for understanding structure–function relations. Cryogenic electron tomography (cryo-ET) is a powerful method for obtaining this critical information. However, cryo-ET studies are challenging and often limited to a small number of cell types per study. Here, we collate cryo-ET data from hundreds of cells and tissues across the biosphere to i) identify emerging methodological trends, ii) pinpoint strategies to reduce imaging time and costs, iii) quantitatively compare methods for cell freezing and sectioning, and iv) census cryo-ET species coverage across all domains of life. Comparing the fraction of cellular material within a single lamella across all domains of life reveals an order of magnitude difference between eukaryotes (1%) compared to bacteria (9%) and archaea (14%). We calculate the fraction of cellular material which can be imaged using distinct sectioning methods on multicellular communities and tissues—identifying serial lift-out as a powerful approach for obtaining more complete cellular depictions. Finally, we show that the biodiversity of current cryo-ET studies is 2 to 3 orders of magnitude lower than in sequence libraries and 4 to 5 lower than the total predicted on Earth. Our analyses reveal major evolutionary lineages which remain critically understudied and highlight where future cryo-ET research would be most impactful.