Gene for Pregnant Male Fish Found

A pipefish, which is in the seahorse family. Image credit: Asther Lau Choon Siew, Dreamstime.com

A new gene discovered in the gulf pipefish hints as to how a family of fish came to adopt male pregnancy.

Male gulf pipefish—a member of the seahorse family—receive eggs from their female counterparts, then fertilize and carry them in a protective pouch. Among other functions, the pouch regulates the saline content in the wombs.

The researchers found a gene—dubbed patristacin—that provides cell instructions to make astacin, a family of proteins that performs a range of functions in bony fish. As a new species begins to evolve, some genes are copied. The new gene copies can take on new roles while the initial genes continue performing their original tasks.

Patristacin, the researchers note, is not a copy, but a gene that has taken on a second job. Thousands of years ago, this gene was most likely involved in kidney and liver function but has since started supporting the pouch of male gulf pipefish.

"We think it was a new job for an old gene—genetic moonlighting, so to speak,” said April Harlin-Cognato, a researcher from Michigan State University. “At this point we know the gene codes for a protein in the brood pouch during male pregnancy, but we don't know yet what it is doing in the brood pouch. It's a whole new ball of wax to understand how this gene functions in its new job."

Patristacin can be found in the pouch of seahorses and pipefish and in the kidney and liver of bony fish.

"The genes show you ancestry," Harlin-Cognato said. "They show you the overall family tree and can tell you when things took place during the evolution of a new structure. From this family tree we can make educated guesses about the structure and function of these proteins. We're looking at the endpoint and trying to reconstruct its origin. It's like doing genetic archaeology."

The results are detailed in this week’s edition of the Proceedings of the National Academy of Sciences.

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