How do marine worms adapt to deep-sea conditions?

Maeva Perez is fascinated by marine worms. Her first encounter with these cold-blooded invertebrates dates back to her time at the University of Victoria, in British Columbia, where she was completing a master’s in biology. Her thesis was on the symbiotic relationship between a species of marine worm and the bacteria in its environment that helped the worm adapt to a seemingly inhospitable ecosystem at the bottom of the Pacific Ocean.

Perez's fascination grew at Université de Montréal, where she recently completed a doctorate in the laboratory of Bernard Angers, a professor in the Department of Biological Sciences with whom Perez had previously interned. But before delving deeper into this family of annelid worms (from the Latin annelida, or “little ring"), Perez wanted to know a little more about their genetics.

Epigenetics plays a role

Having studied the worms’ symbiosis with bacteria in detail, Perez is now investigating how epigenetics influences the ability of marine worms to adapt.

“The role of epigenetics in species evolution and resilience is getting a lot of scientific attention right now,” said Perez. “Epigenetics looks at all of the processes involved in gene expression, or non-expression. If you think of a genome as a book that contains all the instructions for creating a living being, epigenetics is the program that determines which parts of the book are used and when.”

One of the mechanisms by which epigenetics operates is DNA methylation. “Methylation is an epigenetic regulation process that chemically modifies some of the nitrogen bases in DNA,” Perez explained. “It’s been well studied in vertebrates, but not so much in invertebrates, let alone in annelid worms. It plays a role in environmental acclimatization, making organisms living in habitats where conditions are unpredictable and highly variable more resilient to environmental changes.”

Methylation occurs mostly in gene regulatory regions, inhibiting gene expression.

A different kind of methylation

Methylation serves two parallel functions: inhibiting and stabilizing gene expression. When the enzymes involved in converting DNA to RNA make a mistake and produce incomplete RNA molecules, methylation lets cells recognize and eliminate the incomplete molecules. However, energy is lost in the process.

“In the marine worms that we studied, the methylation seems to occur mostly in the body of the gene, whereas in vertebrates, it happens in the DNA control regions,” said Perez. “So it seems to be supporting gene expression, rather than inhibiting it.”

When hydrostatic pressure on the worms increases, it changes the shape of the proteins, making them less effective. But the methylation profiles of the three annelid species Perez studied indicate that the functions associated with repairing or eliminating malformed proteins seem to be specifically targeted for increased regulation.

“That suggests that epigenetic regulation by DNA methylation could be an adaptive mechanism that counteracts the effects of hydrostatic pressure at the bottom of the ocean,” Perez said.

Excellent ecosystems to study

Perez believes the hydrothermal vents and hydrocarbon seeps found on the deep ocean floor are excellent ecosystems for studying the ecological and evolutionary roles of DNA methylation, since the environmental conditions are highly variable in time and space.

Perez recently began a postdoctoral fellowship in Hong Kong, where she plans to continue studying DNA methylation in other marine worm species, as well as study their phylogeny, i.e. their evolutionary history and relationships.

“We still don’t know how these worms wound up at the bottom of the ocean but we think they came from the surface and colonized the depths several million years ago,” Perez said. “Their phylogeny isn’t clear and that is what I’ll be exploring, making connections with paleoceanography, for their ecosystems are connected to our own.”