# Ancestral neuronal receptors are bacterial accessory toxins

## TL;DR

This paper shows that Teneurins, important for neuronal communication in animals, evolved from bacterial toxins used in cell interactions.

## Contribution

The paper reveals that metazoan Teneurins are repurposed bacterial toxins, providing new insight into the evolutionary origin of neuronal receptors.

## Key findings

- Bacterial Teneurins form toxin-encapsulating structures and are found in species with complex social behaviors.
- Metazoan Teneurins evolved from bacterial toxins and are essential for intercellular communication in nervous systems.
- Teneurin-like proteins are widespread in bacteria but limited to specific species with immunity gene co-expression.

## Abstract

Horizontal gene transfer events were crucial in the emergence of multicellular life. A striking example is the acquisition of Teneurins, putative surface-exposed toxins in bacteria that function as cell adhesion receptors in metazoan neuronal development. Here, we demonstrate the evolutionary relationships between metazoan and bacterial Teneurins. We use cryogenic electron microscopy and bioinformatic analysis to show that bacterial Teneurins harbour a toxic protein in a proteinaceous shell. They are rare but widely distributed across bacterial taxa and are predominantly seen in species with complex social behaviours, suggesting roles in cell-to-cell interaction. This work confirms that metazoan Teneurins are repurposed bacterial toxins that have evolved to be essential mediators of intercellular communication in all advanced nervous systems. Their acquisition was a key event in the evolution of metazoans.

Previous studies of Teneurins identified an uncharacterized family of Teneurin-like proteins in bacteria. Here, the authors show these proteins are widespread across both Gram groups but limited to certain species, where they form barrel-like structures that encapsulate a toxin and are co-expressed with potent immunity genes.