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Contact: Diana Kenney, Marine Biological Laboratory

WOODS HOLE, Mass.—How a brilliant-green sea slug manages to live for months at a time “feeding” on sunlight, like a plant, is clarified in a recent study published in The Biological Bulletin.

The authors present the first direct evidence that the emerald green sea slug’s chromosomes have some genes that come from the algae it eats.

These genes help sustain photosynthetic processes inside the slug that provide it with all the food it needs.

Importantly, this is one of the only known examples of functional gene transfer from one multicellular species to another, which is the goal of gene therapy to correct genetically based diseases in humans.

“Is a sea slug a good [biological model] for a human therapy? Probably not. But figuring out the mechanism of this naturally occurring gene transfer could be extremely instructive for future medical applications,” says study co-author Sidney K. Pierce, an emeritus professor at University of South Florida and at University of Maryland, College Park.

The rich green color of the photosynthesizing sea slug, Elysia chlorotica, helps to camouflage it on the ocean floor. Credit: Patrick Krug

The rich green color of the photosynthesizing sea slug, Elysia chlorotica, helps to camouflage it on the ocean floor. Credit: Patrick Krug

The team used an advanced imaging technique to confirm that a gene from the alga V. litorea is present on the E. chlorotica slug’s chromosome. This gene makes an enzyme that is critical to the function of photosynthetic “machines” called chloroplasts, which are typically found in plants and algae.

It has been known since the 1970s that E. chloritica “steals” chloroplasts from V. litorea (called “kleptoplasty”) and embeds them into its own digestive cells. Once inside the slug cells, the chloroplasts continue to photosynthesize for up to nine months—much longer than they would perform in the alga. The photosynthesis process produces carbohydrates and lipids, which nourish the slug.

How the slug manages to maintain these photosynthesizing organelles for so long has been the topic of intensive study and a good deal of controversy. “This paper confirms that one of several algal genes needed to repair damage to chloroplasts, and keep them functioning, is present on the slug chromosome,” Pierce says. “The gene is incorporated into the slug chromosome and transmitted to the next generation of slugs.” While the next generation must take up chloroplasts anew from algae, the genes to maintain the chloroplasts are already present in the slug genome, Pierce says.

“There is no way on earth that genes from an alga should work inside an animal cell,” Pierce says. “And yet here, they do. They allow the animal to rely on sunshine for its nutrition. So if something happens to their food source, they have a way of not starving to death until they find more algae to eat.”

This biological adaptation is also a mechanism of rapid evolution, Pierce says. “When a successful transfer of genes between species occurs, evolution can basically happen from one generation to the next,” he notes, rather than over an evolutionary time scale of thousands of years.


Schwartz JA, Curtis NE, and Pierce SK (2014) FISH labeling reveals a horizontally transferred algal (Vaucheria litorea) nuclear gene on a sea slug (Elysia chlorotica) chromosome. Biol. Bull. 227: 300-312.


The Biological Bulletin is a peer-reviewed, trans-disciplinary international journal that publishes outstanding experimental research on a wide range of organisms and biological topics, with a focus on marine models. Published since 1897 by the Marine Biological Laboratory, it is one of America’s oldest and most respected journals.

The Marine Biological Laboratory (MBL) is dedicated to scientific discovery and improving the human condition through research and education in biology, biomedicine, and environmental science. Founded in Woods Hole, Massachusetts, in 1888, the MBL is a private, nonprofit institution and an affiliate of the University of Chicago.

MBL Adjunct Scientist Amy Gladfelter can now add “video producer” to her resume. Tapped to make her science “visible to the world” by Celldance Studios, a project of the American Society for Cell Biology (ASCB), Gladfelter came up with an aesthetically beautiful, simply told video about her discoveries of what goes wrong when cells form toxic aggregates, such as in Alzheimer’s disease. Her mini-movie, called “Companions in Discovery,” was filmed partly at MBL and partly at Dartmouth College, where she is an Associate Professor of Biological Sciences. It premiered for an appreciative audience in December at the ASCB annual meeting in Philadelphia.

“I like the end of the film, where members of [Gladfelter’s] lab talk briefly on camera. These young faces are the future of cell biology,” said Simon Atkinson, chairman of the ASCB’s Public Information Committee, which sponsors Celldance Studios.

Celldance Studios gave Gladfelter $1,000 to underwrite her costs, and provided video editing and post-production support. The original score is by Hollywood film composer Ted Masur, son of cell biologist Sandra Masur. More information is here.


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By Wallace Marshall
Co-director, MBL Physiology Course

Last month, I had a problem. I was teaching in the MBL Physiology course, using the giant, single-celled organism Stentor as a model system for students to learn quantitative approaches in cell biology. Stentor, which live in ponds, eat by creating a vortex of water that drags food into the cell’s mouth. The flow is created by thousands of cilia—tiny, hair-like cell parts that swing back and forth pushing fluid around. (Cilia are also critical for making the mucus in your airway flow away from your lungs, and patients with defects in these cilia can be really sick. So the question of how cilia make fluid flow is very important from a medical perspective. )

Stentor is a genus of large, trumpet-shaped ciliates, commonly found in freshwater ponds. Credit: EOL / micro*scope

Stentor is a genus of large, trumpet-shaped ciliates, commonly found in freshwater ponds. Credit: EOL / micro*scope

One of the students in our class, Shashank Shekhar from the CNRS Institute, France, had become interested in how the cell generates this pattern of fluid flow. Shashank started tracking the flow by putting small plastic beads into the water around the Stentor and then taking video images of the beads moving. This is a pretty standard approach in fluid dynamics called particle image velocimetry (PIV). But it’s not that commonly used in biology, and we didn’t entirely know what we were doing. The software we had been trying to use to track these particles didn’t give really nice flow lines. So this was the problem: How to use the flow of these tiny beads to figure out the pattern of flow around the cell as it feeds.

Frustrated by this problem, I decided to go get some coffee from Woods Hole Market. On the way back, I ran into my colleague Magdalena Bezanilla, an MBL Whitman Investigator from University of Massachusetts, Amherst, who works on cell biology. She thinks a lot about things moving inside cells so I figured I could get her input into our PIV challenge.

We ended up chatting about the problem in the MBL’s Waterfront Park, and while we were talking, a couple of guys emerged from the harbor in full scuba gear, carrying a huge metal bracket upon which was mounted a video camera and a laser. (This would be quite weird back home but it’s business as usual in Woods Hole.) I asked the guys what they were up to and they said they were using PIV to study the flow of fluid around ctenophores! Ctenophores or comb jellies are jellyfish-like animals that swim using cilia. So at the exact moment that we were pondering how to use PIV to track cilia-generated fluid flow in our single-celled organisms in the Physiology course, a guy walks out of the water and announces that he is doing the exact same thing, for comb jellies! (Those people who say that Woods Hole is a magical place are telling the truth.)

The guys with the scuba gear and lasers were Jack Costello of Providence College and Sean Colin of Roger Williams University, Whitman Investigators working for the summer at the MBL. Jack offered to give us advice about how to analyze our data, so I sent Shashank over to Jack’s lab in the Rowe building. With Jack’s help and expertise, Shashank was able to get beautiful flow lines from his data (see photo), which clearly reveal the pattern of cilia-generated flow around the Stentor cell while it feeds. Our big problem was solved in a single day due to a fortuitous combination of people, courses, coffee breaks, cells, beaches, marine organisms, and advanced technology. And that’s what summer at the MBL is all about.

Fluid flow around Stentor visualized through particle image velocimetry. Courtesy of Wallace Marshall.

Fluid flow around Stentor as it feeds, visualized by particle image velocimetry. Courtesy of Wallace Marshall.

Thank you to Wallace Marshall of the University of California, San Francisco, for contributing this post. All MBL scientists, students, community members, and visitors are invited to submit items for the MBL’s blog. Please contact Diana Kenney:

By Aviva Hope Rutkin

Visiting scientist Guillermo Yudowski wants to make sea anemones happy.

Every morning, he arrives at his MBL laboratory and looks into a group of plastic tanks. Inside are samples of Aiptasia pallida, a hardy strain of anemone found in abundance near the University of Puerto Rico, where Yudowski conducts neurobiological research. Happy A. pallida, he says, are “colorful and open”; sad ones are closed and white. The white samples are near death and will only last three to four days in their containers.

Top view of a day-old spawned Porites spp. coral larvae. Composite image seen under a fluorescent microscope. Symbiotic zooxanthellae autofluorescence in red, larvae epidermis autofluorescence in green. Courtesy of Guillermo Yudowski.

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Turning white—becoming, in Yudowski’s words, “sad”—is called bleaching. The anemone’s tissues are home to zooxanthellae, vibrant photosynthetic algae that produce food for the anemone and give it a characteristic brown color. Bleaching expels this algae from their home. The bleaching process is thought to be triggered by stress: a decrease in light availability, for example, or changes in the water’s temperature or pH. And these changes don’t need to be dramatic. A difference of a couple degrees Celsius can be enough to effectively bleach an anemone.

Yodowski and his colleagues hope their research will point to a cost-effective treatment for bleaching, which poses a serious threat not only to anemones, but to the world’s coral reefs. Though anemones and corals are different, strategies that work for the one organism may be effective for another. The changing climate has already led to mass bleaching events in the Great Barrier Reef, as well as coral reefs in the Indian Sea, the Caribbean Sea, and the Florida Keys.

“If you read the literature, some say that all the coral is going to die in 50 years. Others say, maybe 50 to 100,” says Yudowski. “It doesn’t make a big difference.”

To move toward a solution, Yudowski wants to understand what’s happening to the anemones on a microscopic level. If we figure out why bleaching occurs on a cellular level, then perhaps we can discover how to stop it from happening altogether.

“We don’t really know much about the basic molecular mechanics of the process,” explains Yudowski. “We are trying to understand how stresses like increased ocean temperature and acidification induce the expulsion of the algae.”

Yudowski and his student, Michael Marty-Rivera, are treating anemones with antioxidant compounds found in red wine and green tea. Previous research shows that reactive oxygen species, a kind of chemically reactive molecule, can trigger the bleaching process. Yudowski and Marty-Rivera think that these antioxidants might be able to counteract the effects of these trigger molecules. They will test the efficacy of their treatments by measuring the amount of photosynthetic activity in the anemones, as well as the number of zooxanthellae present.

Yudowski and Marty-Rivera will spend two months at the MBL this summer before returning to the University of Puerto Rico where, in close collaboration with Professors Loretta Roberson and Joshua Rosenthal, they run several different coral research projects. They want to understand the mechanism of calcification in corals and how environmental variables, such as temperature and pH, impact corals’ ability to form reefs and maintain a healthy symbiosis with their zooxanthellae partners.

Funding for the research is provided by the Puerto Rico Center for Environmental Neuroscience and the National Science Foundation Center of Research Excellence in Science and Technology.

Ron Vale may not be the next Woody Allen, but he seems at ease with the role of film director and, you might say, born to the part.

Vale, a Howard Hughes Medical Institute Investigator from the University of California-San Francisco, regularly spends his summers at the MBL as a Whitman Center researcher.

This year, Vale also transformed a conference room in Lillie Laboratory into a mini-Hollywood set. There, he has been videotaping scientists for a site called iBio Seminars, a free, open-access, educational resource Vale founded in 2007 that has blossomed into a treasure trove for anyone interested in the life sciences.

iBio Seminars founder/director Ron Vale frames a shot. Photo by Diana Kenney

iBio Seminars are videos of the world’s best biologists lecturing on topics of their expertise. Some are seminar length, while others are insightful nuggets just a few minutes long. They can be downloaded and used by professors, scientists, journalists, historians of science, or just perused by anyone seeking enlightenment on contemporary biology. A companion to the lectures is iBio Magazine, which has short videos that highlight “the human side of research.”

Vale’s father was a screenwriter, and his mother was an actress before her marriage. When I saw him bounding out of Lillie Laboratory wearing a Motörhead T-shirt the other day, I asked, “Have you always harbored a latent interest in filmmaking?”

“Absolutely not,” he replied firmly, and went on to joke that a modeling contract might be interesting.

Vale’s real rationale for founding iBio Seminars, he said, is that places like MBL, Harvard and UCSF “offer great opportunities to hear scientists talk about their work. It’s a privilege to have that available to us. With the Web, iBio provides a way for students and scientists around the world to hear these talks. The goal of iBio is to make science as available as possible.”

Vale confers with iBio's videographer/digital editor Isaac Conway-Stenzel. Photo by Diana Kenney

This summer at MBL, Vale videotaped a whole gallery of “stars” in biology, many of whom were on campus to teach, lecture or conduct research. They included Gary Borisy, Shinya Inoué, and Roger Hanlon of the MBL; Ed Taylor of University of Chicago; Alfredo Quiñonenes-Hinojosa of Johns Hopkins University; Jack Szostak, Matthew Meselson, Tim Mitchison, Andrew Murray, Xiaowei Zhuang, and Scott Edwards of Harvard University; Nancy Knowlton of Smithsonian Institution; Hugh Huxley of Brandeis University; Avram Hershko of the Technion in Haifa, Israel; and Melissa Moore of UMass Medical School. Vale also filmed a segment about BioBus, a biology classroom on wheels; and one about the state of Indian science and education with Satajit Mayor of NCMS, Bangalore, and Subhash Lakhotia of Banaras Hindu University.

One July morning found Vale prepping Ed Taylor and Gary Borisy (the MBL’s president and director) for an iBio taping. The topic? Their discovery of a fundamental structural protein in cells, now called tubulin, in the mid-1960s when Borisy was a Ph.D. student in Taylor’s lab.

Ed Taylor and Gary Borisy prepare for videotaping in iBio's "chroma key" studio set up in Lillie Laboratory. Photo by Diana Kenney

After a spontaneous and colorful discussion of how the two would enter the frame, Vale began coaching them on the do’s and don’ts of iBio conversations. One bump in the road soon appeared: Taylor and Borisy didn’t have the same version of the tubulin story in their heads. Their chronologies differed slightly; as Borisy noted, “Memories dim and we have different takes on things.”

Vale was nonplussed. “This could be a lot of fun!” he said. He positioned them in front of the “chroma key” green screen, a backdrop similar to what TV weather anchors use, upon which slides, maps, and other visuals would be displayed later, during editing. Vale then encouraged Taylor and Borisy to tell the story of their discovery, and to conclude with a message or lesson to young people about how science really happens.

Ed Taylor and Gary Borisy prepare to tell the story of the discovery of tubulin. Photo by Diana Kenney

With the camera rolling, Taylor and Borisy traveled back nearly half a century to a tale of discovery that included their mutual fascination with understanding how living cells divide, Borisy’s first visit to the MBL, tantalizing leads, intriguing paradoxes, several “red herrings and blind alleys” and ultimately, a fundamental discovery about cell structure that has had widespread and lasting importance.

Taylor’s takeaway lesson? “Choose an important problem when you are just starting out in science. Don’t work on a trivial problem. Then, if you succeed, you’ve really done something good.”

And Borisy’s: “Sometimes you encounter contradictory results, paradoxes. Don’t sweep those under the rug. Resolving those can bring you to your answer.”

Curious about the full story? You’ll just have to see the movie.

iBio Seminars is funded by the Howard Hughes Medical Institute, the American Society for Cell Biology, and the University of California-San Francisco.

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