Secrets of self-defense revealed in sea cucumbers

Sea cucumbers, a type of marine animal and a medicinal food delicacy in south Asia, are fascinating little creatures who dwell on ocean floors. They can produce triterpenoid saponins, a type of molecule that is often produced by plants and rarely produced in animals. But just exactly how sea cucumbers evolved to produce triterpenoid saponins has always stumped scientists. 

In a new study, researchers at the John Innes Centre explored the sea cucumber genome and compared it to other echinoderms such as sea urchins and starfish. 

“Soft-bodied slow-moving sea creatures such as sea stars and sea cucumbers lack an adaptive immune system and have instead evolved the ability to make specialized protective chemicals (glycosylated steroids and triterpenes) as part of their innate immune system,” wrote the researchers. “This raises the intriguing question of how these biosynthetic pathways have evolved.”

The analysis revealed that sea cucumbers lack an enzyme that produces sterol, a type of steroid necessary to build cell membranes and hormones. 

It turns out that sea cucumbers have redirected the sterol-producing function into two new genes with different purposes. Once scientists discovered these genes, they isolated them and transferred them to yeast so the extractions could be further studied. 

The researchers discovered that these genes have two functions. The first is to make a type of saponin that is used for self-defense. Secondly, the genes produce molecules that protect the sea cucumbers from their own defense mechanisms.

The experts hope to synthesize the chemicals made by these genes using plants or yeast. Not only would this alternative be cheaper, but it could save lives. 

Sea cucumbers are a multi-billion dollar industry. However, in some parts of the world, they are endangered. The ability to produce their healthful chemicals in plants or yeast is more humane and could benefit conservation efforts. 

“Sea cucumbers are massively important in Asia as a health benefiting food source and for traditional medicines,” said study co-author Professor Anne Osbourn. “So, if we can understand how their molecules are made, we can make these high value compounds without needing to grind up sea cucumbers. We can make them using plants or yeast.” 

This study is published in Nature Chemical Biology.

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By Erin Moody , Earth.com Staff Writer