Natures wonders: sea cucumber doesn't poison itself (Introduction)

by David Turell , Monday, July 25, 2022, 18:47 (634 days ago) @ David Turell

Produces toxins to poison predators but not itself:

https://www.the-scientist.com/news-opinion/how-the-sea-cucumber-defends-itself-from-its...

"To protect themselves against predators and pathogens alike, sea cucumbers produce defensive toxins called saponins, as do their close cousins, starfish. However, new research finds that sea cucumbers are the only echinoderms—and among the only animals on Earth—that produce chemicals called triterpenoid saponins, which don’t poison the sea cucumbers themselves thanks to their unique metabolic pathways.

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"Sea star saponins are steroid-based. Triterpenoids and sterols are derived from similar molecules, and the molecular pathways to produce both involve enzymes called oxidosqualane cyclases (OSCs)...To their surprise, the researchers found that sea cucumbers lack the gene that produces LSS entirely, as well as three other enzymes that allow other species to make sterols. Instead, the sea cucumber genome contains two other genes for OSCs.

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"The team discovered that the cucumber OSC genes produced two sterol-like molecules, both of which were involved in triterpenoid production. These molecules also converted compounds into the cholesterol-like molecules that are present in the sea cucumber cell membranes. The molecules function similarly to cholesterol, but their differences help the animals avoid poisoning themselves with saponins.

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"Having two OSC-coding genes, neither of which are for LSS, is “highly exceptional in the animal kingdom,” says Thimmappa. He adds that sea cucumbers are the only known animals to have two OSC-coding genes but not make their own cholesterol."

Comment: Another irreducibly complex arrangement: to protect itself the sea cucumber produces the toxins to cholesterol, a chemical vital to all other forms, and uses a different cholesterol-like molecule to not poison itself. This cannot be evolved stepwise, but put in place all at the same time by design.