How mussel genes may hold key to detecting pollution in water

Blue mussels could help monitor ocean pollution, researchers say. Photo by donieve/Pixabay

By Mikayla Heiss
BU News Service

According to researchers, genetic material reveals a unique opportunity to investigate harmful chemicals inside the hardened shells of mussels. 

By studying responses to compounds, such as synthetic estrogen, at the genomic level, scientists have developed a tool that can determine if a group of chemicals is present, expanding the search for pollutants and acting as a warning system for monitoring efforts, according to Dr. Helen Poynton, a professor at the University of Massachusetts Boston.

“These types of molecular tools, we’re hoping, can provide a head start and say, ‘Look, it looked like something is brewing here. We need to evaluate this further,’” said Poynton, one of the lead authors on the study.

Poynton and other researchers chose to focus on endocrine-disrupting compounds, which interact with hormones responsible for reproduction and development.

Previous research on endocrine disruptors suggests they can negatively affect humans and fish; however, scientists say their impact on invertebrates is often understudied.

“People talk about endocrine-disrupting compounds, but they’re always talking about it in the context of vertebrates,” said Dr. Christopher Vulpe, a professor at the University of Florida and co-author. “There hasn’t been, at least to my knowledge, a systematic effort similar to what’s been done in mammalian and fish systems.” Many endocrine disruptors in vertebrates act primarily through nuclear receptors. These proteins, such as the estrogen receptor, bind to DNA fragments, serving as on-off switches for genes.

Sometime in the past, mussels’ estrogen receptors froze in an active or on form. Ligand bonding became impossible when mutations filled in the binding site. However, shellfish are still impacted by endocrine disruptors.

After exposing mussels to a man-made form of estrogen used in birth control pills, researchers observed female skewed sex ratios and differences in how certain genes were regulated.

“Mussels are definitely affected by what are usually considered to be mammalian endocrine disruptors,” said Poynton. “That was unexpected because their endocrine systems are not very well understood. But because there are millions of years of evolution between shellfish and humans, a lot of people didn’t expect them to be responsive to those types of chemicals.”

By observing how a specific suite of genes are expressed, scientists can determine if endocrine disruptors may be present.

Mussels in Boston Harbor have helped researchers discover upticks in chemical contamination. Photo by Arnstein Rønning/Wikimedia Commons

The use of mussels to detect chemicals is not new. Since 1986, the National Oceanic and Atmospheric Administration has used mussel and oyster tissue to monitor water quality. The program measures for specific chemicals, but this targeted approach overlooks a large percentage of chemicals in production, according to Poynton. Using the more recent method, monitoring programs can broaden their search.

“You could be missing things if you’re just doing targeted chemical analysis,” Poynton said. “One of the advantages of being able to interface a molecular tool [is] it tells you whether effects are occurring, whether you’re looking for that particular chemical or not.”

To verify and build upon the tool, the researchers placed mussels at sites throughout the Boston Harbor. Mussels placed directly over a sewage outflow expectedly had the highest response values.

Although scientists continue to test and develop their knowledge of endocrine disruptors’ impact on mussels, Poynton remains hopeful for the future application of this research.

“[This tool] is a signature of eight different genes that will hopefully help [monitoring programs] distinguish endocrine-disrupting chemicals, ” Poynton said. “Hopefully, this will help to give us a head start on some of these contamination problems.”

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