Tapping Ancient Defence

This marine Hydra is little more than a two-layered cylinder, a tenth the size of a household tap. In evolutionary terms it sits near the base of the animal tree of life, and last shared a common ancestor with humans over 600 million years ago. And yet humans and Hydra have much in common. All animals, regardless of size and complexity, must challenge invading microorganisms and decide whether they are ‘friend’ or ‘foe’. Most, if not all, use proteins called Toll-like receptors to do the job. Toll-like receptors have many functions, but importantly they act as ‘first responders’ that recognise molecular patterns on invading microbes and can turn on a cascading immune response. Here, scientists introduced a green fluorescent protein into the Hydra (right-hand image) and turned off a protein in the immune cascade, helping to confirm that some of Earth’s very first animals used Toll-like receptors to sense bacteria.

Written by Caroline Cross

Caroline Cross

Writer

Fascinated by the complexities of the human body, Caroline enjoys writing about biomedical research. She spent much of her research career peering down a microscope at cells and parasites, and is constantly amazed at their beauty.

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• Sören Franzenburg, Thomas Bosch
• Christian Albrechts University, Kiel, Germany
• Published in PNAS 109(47): 19374-19379