Maeva Perez has explained how marine worms genetically manage to adapt to the extreme conditions of the depths.
Photo credit: Courtesy
Sequencing the DNA of marine worms helps explain how they adapt to life at depths of around 2,500 m under extreme pressure and temperature fluctuations.
Maeva Perez is scientifically in love with marine worms. His first “encounter” with these cold-blooded invertebrates was during his master’s degree in biological sciences at the University of Victoria in British Columbia. His dissertation focused on the symbiosis between a species of marine worm and surrounding bacteria at the bottom of the Pacific Ocean, which contributes to the worm’s adaptation to an ecosystem that at first glance does not seem hospitable.
This love story continued at the University of Montreal, where Maeva Perez has just completed her doctoral thesis in the laboratory of Professor Bernard Angers, where she had already completed an internship in the Department of Biological Sciences. Before she sealed her connection with this family of annelids (or annelids – with marriage in mind!), she wanted to learn more about their genetics…
An extraordinary adaptability
Maeva Perez
Photo credit: Amélie Philibert, University of Montreal
Because from a scientific point of view, the annelids of the deep prove to be irresistible: they live in absolute darkness near hydrothermal vents, which are about 2500 m under water, and are also exposed to pressures 300 times higher than those at The surface is exposed to temperature fluctuations between 60 and 2 °C.
Their presence was discovered in the early 20th century during a deep diving expedition, but it was not until 1977 that they were first spotted in the underwater mountains of the eastern Pacific, where water – heated by magma underground – bubbles up from thermal vents at a temperature of 300°C.
“These worms play a very important ecological role in the ecosystems in which they live, because they create new habitats and enable the establishment of many other species,” emphasizes Maeva Perez. Deep sea marine ecosystems are now threatened by mining interests and there is an urgent need to better understand their ecology, their evolution and their resilience to human activities.”
The role of epigenetics in the adaptability of species
In addition to the adaptation of worms through symbiosis with bacteria, which she has studied extensively, Maeva Perez is now researching the role of epigenetics in the adaptability of marine worms.
“The role of epigenetics in the evolution and resilience of species is a growing field of research,” explains the UdeM graduate. Epigenetics deals with all processes involved in the expression or non-expression of genes.
“If we imagine that the genome is a book that contains all the instructions for creating a living thing, epigenetics is the program that dictates which parts of the book to use and when,” she explains.
And one of the mechanisms of epigenetics is DNA methylation.
“Methylation – a chemical modification of some nitrogen bases in DNA – is a form of epigenetic control that is often studied in vertebrates, which is not the case in invertebrates and even less so in worms and annelids,” adds Maeva Perez. “Methylation is an acclimatization mechanism that allows organisms living in habitats with unpredictable and variable conditions to be more resilient to environmental changes.”
Methylation occurs mainly in the regulatory regions of genes and prevents their expression.
Three species of marine worms are studied
Two of the three species of marine worms examined live near a thermal spring at a depth of around 2500 m.
Photo credit: Courtesy
In her research, Maeva Perez examined three species of worms found in the deep sea, namely Paraescarpia echinospica, Ridgeia piscesae and Paralvinella palmiformis.
The specimens were recovered by engineers who, during an expedition on the high seas, remotely controlled a robot that was connected to the research boat via a cable several kilometers long. Using an arm equipped with tongs, the robot captured the invertebrates, which ranged in size from 10 to 30 cm – some reaching a size of up to 1.5 m.
Using new technology that uses artificial intelligence, DNA and its associated methylation marks can be sequenced simultaneously.
“Detecting methylation usually requires chemical treatment of DNA, which is expensive and complicated,” she says. We have shown that third-generation sequencing technologies, which are still used in genome sequencing projects, also provide very precise information about the epigenetic state of DNA.”
Methylation different than in vertebrates
Methylation has two parallel functions: suppressing gene expression and stabilizing yield. In the latter case, the enzymes that convert DNA into RNA sometimes make mistakes and produce incomplete RNA. The cells are then able to recognize and eliminate this incomplete RNA, but this leads to a loss of energy.
“However, in the marine worms studied, methylation occurs more often in the body of the gene, unlike in vertebrates, where methylation occurs in the control regions of the DNA,” explains Maeva. Perez. This therefore appears to favor the expression of genes rather than their repression.
So as the hydrostatic pressure on these worms increases, the shape of the proteins changes and they become less effective. However, the methylation profile of the three annelid species suggests that functions associated with the repair or removal of malformed proteins appear to be specifically upregulated.
“This suggests that epigenetic regulation through DNA methylation may be an adaptive mechanism that counteracts the effects of seafloor hydrostatic pressure,” she continues.
Ecosystems to explore and preserve
For Maeva Perez, hydrothermal vents and deep-seafloor hydrocarbon vents represent ecosystems of choice for studying the ecological and evolutionary role of DNA methylation because environmental conditions there vary greatly in time and space.
In her postdoctoral fellowship in Hong Kong, which she has just started, she would like to further research the DNA methylation of other species of marine worms and deal with their phylogeny, i.e. with the study of their evolution and their relationships.
“We don’t yet know how these worms got to the bottom of the oceans, but we think they came from the surface and colonized the depths several million years ago,” she concludes. Their phylogeny is not yet clear and that will be my mission, connecting elements of paleoceanography, because the ecosystems in which they live are connected to us!”
For better and not for worse…
Maeva Perez’s full study was published in August in the journal Molecular Biology and Evolution under the title “Third-Generation Sequencing Reveals the Adaptive Role of the Epigenome in Three Deep-Sea Polychaetes.”
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