# Integrins mediate symbiont-specific uptake in cnidarian larvae

## TL;DR

This study shows that integrins help cnidarian larvae recognize and take up specific symbiotic algae, which is crucial for coral reef health.

## Contribution

The study identifies integrins as key receptors for symbiont-specific uptake in cnidarians, expanding their known role in phagocytosis.

## Key findings

- Integrins are highly expressed in the gastrodermal tissue where symbiosis occurs.
- Blocking integrin binding sites reduces symbiont uptake but not non-symbiotic algae uptake.
- Human cells overexpressing integrins can take up symbiotic algae, confirming integrin function.

## Abstract

Endosymbiosis between dinoflagellate algae and cnidaria is fundamental for coral reef health. Appropriate symbiont selection is required for sufficient host nutrient acquisition and could be tailored to increase cnidarian stress tolerance. Previous research suggested glycan–lectin interactions facilitate symbiont uptake; however, blockage of such interactions does not fully inhibit symbiosis establishment, suggesting other receptors are at play. Here, we use a combination of cnidarian model systems and human cell lines to determine if phagocytic integrins facilitate symbiont recognition and uptake. Integrins are highly expressed in the gastrodermal tissue of the host, where symbiosis takes place, and symbiont uptake alters the expression of integrins and downstream signaling molecules. Blockage of integrin binding sites with competitor peptides reduces symbiont uptake, while uptake of non-symbiotic algae, or uptake in a non-symbiotic cnidarian, is unaffected. Finally, overexpression of phagocytic integrins in human cells increases symbiont uptake, and mutation of the active binding site abolishes uptake. Our findings reveal integrins as important receptors for symbiosis establishment and shed light on the evolutionary functions of integrins during phagocytosis.

Many anemone and coral species produce offspring that must phagocytose symbiotic algae from their environment. Arginine-Glycine-Aspartic Acid (RGD) binding integrins allow the host to distinguish between symbionts and non-symbionts and facilitate symbiont uptake.

The sea anemone Aiptasia encodes a single Arginine-Glycine-Aspartic Acid (RGD) binding integrin.Blockage of RGD-binding integrins inhibits uptake of symbiotic dinoflagellates in cnidarian hosts.Host cells use RGD-integrins to distinguish between symbiotic and non-symbiotic algae.

The sea anemone Aiptasia encodes a single Arginine-Glycine-Aspartic Acid (RGD) binding integrin.

Blockage of RGD-binding integrins inhibits uptake of symbiotic dinoflagellates in cnidarian hosts.

Host cells use RGD-integrins to distinguish between symbiotic and non-symbiotic algae.

Many anemone and coral species produce offspring that must phagocytose symbiotic algae from their environment. Arginine-Glycine-Aspartic Acid (RGD) binding integrins allow the host to distinguish between symbionts and non-symbionts and facilitate symbiont uptake.