Study Shows How Marine Animal Produces Unlimited Eggs, Sperm Over Its Lifetime

A microscopic view of Hydractinia

A top-down view of a little-known ocean-dwelling creature most commonly found growing on dead hermit crab shells

Photo: ANDY BAXEVANIS, NHGRI

A little-known ocean-dwelling creature most commonly found growing on dead hermit crab shells may sound like an unlikely study subject for researchers, but this animal has a rare ability—it can make eggs and sperm for the duration of its lifetime. This animal, called Hydractinia, does so because it produces germ cells, which are precursors to eggs and sperm, nonstop throughout its life. Studying this unique ability could provide insight into the development of the human reproductive system and the formation of reproductive-based conditions and diseases in humans.

“By sequencing and studying the genomes of simpler organisms that are easier to manipulate in the lab, we have been able to tease out important insights regarding the biology underlying germ cell fate determination—knowledge that may ultimately help us better understand the processes underlying reproductive disorders in humans,” said Dr. Andy Baxevanis, director of NHGRI’s computational genomics unit and co-author of the paper. 

In a study published in the journal Science, collaborators at NHGRI, the National University of Ireland, Galway, and the Whitney Laboratory for Marine Bioscience at the University of Florida, Augustine, reported that activation of the gene Tfap2 in adult stem cells in Hydractinia can turn those cells into germ cells in a cycle that can repeat endlessly.

In comparison, humans and most other mammals generate a specific number of germ cells only once in their lifetime. Therefore, for such species, eggs and sperm from the predetermined number of germ cells may be formed over a long period of time, but their amount is restricted. An international team of researchers has been studying Hydractinia’s genome to understand how it comes by this special reproductive ability.

Interestingly, the Tfap2 gene also regulates germ cell production in humans, in addition to its involvement in myriad other processes. However, in humans, the germ cells are separated from non-germ cells early in development. Still, despite the vast evolutionary distance between Hydractinia and humans, both share a key gene that changes stem cells into germ cells.