# Asgard archaea: have we found our microbial ancestors?

## TL;DR

Asgard archaea are the closest prokaryotic relatives of eukaryotes and provide insights into the origin of eukaryotic cells.

## Contribution

This review highlights how Asgard archaea represent a key link in understanding the evolutionary transition to eukaryotic cells.

## Key findings

- Asgard archaea possess eukaryotic signature proteins, supporting their close relationship to eukaryotes.
- Earlier observations of shared molecular features between archaea and eukaryotes foreshadowed the discovery of Asgards.

## Abstract

The discovery of Asgard archaea about a decade ago has greatly reshaped our understanding of archaeal evolution and the origin of eukaryotes. Asgards are currently thought to be the closest prokaryotic relatives of eukaryotes and to represent the archaeal host lineage that participated in the endosymbiotic event leading to the first eukaryotic cell. The presence of numerous eukaryotic signature proteins in Asgard genomes supports this view and provides important insights into the deep evolutionary roots of eukaryotic cellular complexity. However, the close relationship between archaea and eukaryotes had been observed for decades, based on features that are shared in different molecular processes. This review discusses the discovery of Asgard archaea in the broader context of archaeal molecular and cellular biology and highlights how earlier findings foreshadowed their emergence. Primarily targeted at newcomers to the field, the review provides an overview of evolutionary innovations across the Archaea domain and discusses molecular and cellular features of cultivated Asgard strains in light of previous archaeal research.

This article discusses the striking similarities between some archaeal lineages and eukaryotes.