Key reproductive hormone in oldest vertebrate identified

Researchers have unravelled the once-prized enigma behind the sex life of the oldest vertebrate — a hagfish — by identifying the first reproductive hormone, a gonadatropin, in the eyeless, snot-covered, worm-like scavenger of the deep.

University of New Hampshire's professor Stacia Sower and colleagues at two Japanese universities have identified the first reproductive hormone in a hagfish.

"This is a significant breakthrough with hagfish," said Sower.

Gonadatropins (GTHs) are proteins secreted from the pituitary gland, stimulating the gonads (ovaries and testes) to produce and release the sex steroid hormones, which prompt their growth and maturation.

GTHs are produced in response to hypothalamic gonadotropin-releasing hormone (GnRH), what Sower calls the 'master molecule' for reproduction in vertebrates. Its discovery remains the holy grail of understanding hagfish reproduction.

At 500 million years old, hagfish are the oldest living vertebrate, predating the dinosaurs. They are notoriously difficult to study, in part because their habitat is the ocean floor at 100 metres or more.

Despite their vicious nature and least appealing characteristic — the stress-induced secretion of mucous from up to 200 slime glands along their bodies — hagfish are prized, particularly in Asian markets. Their tough, soft skin is marketed as 'eel' skin for wallets, belts and other items.

The findings were published in the journal Proceedings of the National Academies of Science (PNAS).