MBL


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.

Jim Motavalli, one of 12 journalists who recently spent 10 days in Woods Hole and at Hubbard Brook, NH, learning the ropes of ecosystems field science, reflects on his experience here. Jim took part in the Logan Science Journalism Fellowship program, which has been offered at the MBL since 1987.

 

Core sampling at Harvard Forest. Photo by KM Kowalski

An SJP fellow core sampling at Harvard Forest in 2012. Photo by KM Kowalski

 

Paloma T. Gonzalez-Bellido, who is now a postdoctoral scientist at the Marine Biological Laboratory (MBL), and colleagues from Howard Hughes Medical Institute, University of Minnesota, and Union College have been awarded a 2012 Cozzarelli Prize by the editorial board of Proceedings of the National Academy of Sciences (PNAS).

Gonzalez-Bellido and colleagues were honored for the “scientific excellence and originality” of their study of prey detection and interception in dragonflies.

The research was performed at Howard Hughes Medical Institute’s Janelia Farm Research Campus, where Gonzalez-Bellido was a postdoctoral scientist prior to joining the MBL’s Program in Sensory Physiology and Behavior in September 2011.

The study provides insight into basic visual-motor neural processing, and has implications for the development of “bioinspired” prosthetics for humans.

Green Darner Dragonfly Credit CC:Brian Robert Marshall

A green darner dragonfly, a member of the Aeshnidae family, in which Robert Olberg of Union College originally discovered the target-selective descending neurons (TSDNs). Credit: Brian Robert Marshall/Wikimedia

“I am honored to receive recognition for this work, for which we bridged the clinical and neuroethological fields, and developed new techniques,” says Gonzalez-Bellido. “This award has provided me with fuel to keep up the hard work and further my research plans.”

In order for a dragonfly to intercept its prey in midair (which dragonflies do with a 95% success rate), it needs to quickly track the prey and predict its future location. To understand how they undertake this complex task, Gonzalez-Bellido and her co-authors studied a small group of 16 motor neurons, called target-selective descending neurons (TSDNs), in the dragonfly Libellula luctuosa. These neurons, originally discovered by co-author Robert M. Olberg (Union College) in the green darner dragonfly, originate in the brain and extend to the thoracic ganglia, where the neural signal is interpreted and translated into wing muscle movements. Surprisingly, the scientists found that this small group of neurons can detect the direction of target prey with high accuracy and reliability across 360 degrees, and that this information is relayed from the brain to the wing motor centers in population vector form.

In 1988, co-author Apostolos Georgopoulos and his colleagues showed in monkeys that from the activity of neurons in the motor cortex, the population vector algorithm can predict the monkey’s upcoming arm movement. However, to achieve a more accurate prediction with this algorithm, upwards of 200 neurons were needed. Thus, the present discovery that a highly accurate neural code carrying information about target direction can be achieved with just 16 neurons is enlightening, and could have applications in the development of bioinspired robots. (Georgopolos is an MD-PhD at the University of Minnesota/Veterans Administration Medical Center who is interested in the development of prosthetics.)

Paloma-Gonzalez-Bellido Credit HHMI:Janelia Farm

Paloma Gonzalez-Bellido. Credit: HHMI/Janelia Farm

Randy Schekman, PhD, editor-in-chief of PNAS, describes the papers chosen for the Cozzarelli Prize as being “of exceptional interest… These papers are not merely technically superior but have had special impact and maybe novel techniques or novel applications of techniques, or very important discoveries.”

For this study, Gonzalez-Bellido and Trever Wardill (then at HHMI) developed a new protocol for labeling and confocal imaging of neurons in thick invertebrate tissue samples. In addition, her co-authors and former HHMI colleagues Hanchuan Peng and Jinzhu Yang developed a method for automatic 3D digital reconstruction (tracing) of neurons in microscopic images.

Gonzalez-Bellido sees the dragonfly as a promising model for understanding the evolution of neural systems. “It’s exciting that the same computation [the population vector algorithm] is used by monkeys and dragonflies for this task. Dragonflies belong to the most ancient groups of flying insects on earth, and they have changed little in 250 million years” she says.

The Cozzarelli Award was established in 2005 and named in 2007 to honor late PNAS editor-in-chief Nicholas R. Cozzarelli. Gonzalez-Bellido and the other awardees will be recognized at an awards ceremony during the National Academy of Sciences Annual Meeting on April 28, 2013, in Washington, D.C.

Out of more than 3,700 papers published in the journal last year, the editors selected Gonzalez-Bellido’s paper and five others for the Cozzarelli Prize.

Citation: 

Gonzalez-Bellido PT, Peng H, Yang J, Georgopoulos AP and Olberg RM (2012) Eight pairs of descending visual neurons in the dragonfly give wing motor centers accurate population vector of prey direction. PNAS 110: 696-701 /doi/10.1073/pnas.1210489109

A PNAS commentary on the paper is here.

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Senior Scientist Rudolf Oldenbourg and other MBL-affiliated biologists and physicists revealed their collaborative process to create informative, beautiful images of cell structure and behavior at the American Association for the Advancement of Science (AAAS) meeting last weekend in Boston, Mass.

The symposium “Innovations in Imaging: Seeing is Believing” was organized by Amy Gladfelter of Dartmouth College, an MBL Whitman Investigator.

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Fluorescence image of a living cell (MDCK) expressing septin molecules linked to green fluorescent protein (GFP). The image was recorded with the Fluorescence LC-PolScope and shows fluorescent septin fibers in color, indicating that the fluorescence is polarized and the septin molecules are aligned in the fibers. Credit: Rudolf Oldenbourg/MBL

“We are beginning to understand the basis for cell organization at unprecedented spatial and temporal resolution through the creative application of fundamental physics to microscopy,” Gladfelter stated. “This symposium will help motivate the next phase of interdisciplinary approaches to advance the visualization of life, from the scale of a single molecule to the whole organism.”

The data collected in biological images, Gladfelter noted, not only illuminates basic cellular processes, but is useful for medical purposes: to diagnose a metastasizing cancer or microbial infection, for example, or to screen chemical libraries for new pharmaceuticals.

“These images bring us to a beautiful world beyond the grasp of our normal senses,” Gladfelter stated. “In this way microscopes give us beauty and [biological or medical] application, often in the same image.”

The capacity of microscopes to reach beyond the senses is well appreciated by Oldenbourg, who spoke on New Frontiers in Polarized Light Microscopy for Live Cell Imaging.
(Oldenbourg’s MBL co-authors are Michael Shribak, Tomomi Tani, and Shinya Inoué.)

“Polarization is a basic property of light that is often overlooked, because the human eye is not sensitive to polarization. Therefore, we don’t have an intuitive understanding of it and optical phenomena that are based on polarization either elude us or we find them difficult to comprehend,” Oldenbourg stated.

“Like most scientific instruments, the polarized light microscope translates polarization effects so they can be perceived by our senses, in this case by our eyes, and makes them amenable to quantitative and analytical analysis. At the MBL, we are developing polarized light imaging techniques, including fluorescence polarization … for generating time-lapse images that clearly reveal the otherwise invisible dynamics of single molecules and molecular assemblies in organelles, cells, and tissues.”


The events of cell division during meiosis I in a living insect spermatocyte, beginning at diakinesis through telophase to the near completion of cytokinesis. Testes from the Crane fly Nephrotoma suturalis were observed with time-lapse liquid crystal polarized light microscopy (LC-PolScope, MBL, Woods Hole MA, and PerkinElmer, Hopkinton MA). Movie images display the naturally occurring birefringence of cell organelles and structures that are made up of aligned molecules, such as the meiotic spindle and mitochondria. Horizontal image width is 56 µm. Credits: James LaFountain and Rudolf Oldenbourg/MBL

Other talks in the symposium included:

Navigating the Dynamic Cell
Jennifer Lippincott-Swartz (National Institutes of Heath/MBL Physiology Course)

Imaging Three-Dimensional Dynamics in Cells and Embryos
Eric Betzig (Howard Hughes Medical Institute/MBL Physiology Course and MBL Neurobiology Course)

Structured Illumination and the Analysis of Single Molecules in Cells
Rainer Heintzmann (King’s College, London)

Imaging Single Cells in the Breast Tumor Microenvironment
John Condeelis (Albert Einstein College of Medicine)

Single Molecule Imaging in Live Cells
Amy S. Gladfelter (Dartmouth College/MBL Whitman Investigator)

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Among the animals that are appealing “cover models” for scientific journals, lancelets don’t spring readily to mind. Slender, limbless, primitive blobs that look pretty much the same end to end, lancelets “are extremely boring. I wouldn’t recommend them for a home aquarium,” says Enrico Nasi, adjunct senior scientist in the MBL’s Cellular Dynamics Program. Yet Nasi and his collaborators managed to land a lancelet on the cover of The Journal of Neuroscience last December. These simple chordates, they discovered, offer insight into our own biological clocks.

The head of the marine invertebrate amphioxus (Branchiostoma floridae), magnified 15 times. Amphioxus are the most ancient of the chordates (animals whose features include a nerve cord), according to molecular analysis. They are important to the study of the origin of vertebrates. Photo by Maria del Pilar Gomez. Click for larger version.

Nasi and his wife, MBL adjunct scientist Maria del Pilar Gomez, are interested in photo-transduction, the conversion of light by light-sensitive cells into electrical signals that are sent to the brain. The lancelet, also called amphioxus, doesn’t have eyes or a true brain. But what it does have in surprising abundance is melanopsin, a photopigment that is also produced by the third class of light-sensitive cells in the mammalian retina, besides the rods and cones. This third class of cells, called “intrinsically photosensitive retinal ganglion cells” (ipRGCs), were discovered in 2002 by Brown University’s David Berson and colleagues. Now sometimes called “circadian receptors,” they are involved in non-visual, light-dependent functions, such as adjustment of the animal’s circadian rhythms.

“It seemed like colossal overkill that amphioxus have melanopsin-producing cells,” Nasi says. “These animals do nothing. If you switch on a light, they dance and float to the top of the tank, and then they drop back down to the bottom. That’s it for the day.” But that mystery aside, Gomez and Nasi realized that studying amphioxus could help reveal the evolutionary history of the circadian receptors.

Amphioxus can grow as long as 2.5 inches and are typically found half-burrowed in sand. Photo by Hans Hillewaert.

As so it has. In 2009, Gomez and Nasi isolated the animal’s melanopsin-producing cells and described how they transduce light. In their recent paper, they tackled the puzzling question of why the light response of these amphioxus cells is several orders of magnitude higher than that of their more sophisticated, presumed descendents, the ipRGCs. (In mammals, the ipRGCs relay information on light and dark to the biological clock in the hypothalamus, where it is crucial for the regulation of circadian rhythms and associated control of hormonal secretion.)

By detailing how the large light response occurs in the amphioxus cells, Gomez and Nasi could relate their observations to the functional changes that may have occurred as the circadian receptors evolved and “eventually tailored their performance to the requirements of a reporter of day and night, rather than to a light sensor meant to mediate spatial vision.” The light-sensing cells of amphioxus, they discovered, may be the ”missing link“ between the visual cells of invertebrates and the circadian receptors in our own eyes.

Citations

Ferrer C., Melagón G., del Pilar Gomez M., and Nasi E. (2012) Dissecting the Determinants of Light Sensitivity in Amphioxus Microvillar Photoreceptors: Possible Evolutionary Implications for Melanopsin Signaling. J. Neurosci. 32: 17977-17987.

del Pilar Gomez M., Angueyra J.M, and Nasi E. (2009) Light-transduction in melanopsin-expressing photoreceptors of Amphioxus. PNAS 16: 9081-9086.

Enrico Nasi and Maria Gomez (second and third from left) with some of their students from the Universidad Nacional, de Colombia, where they hold faculty appointments. Nasi and Gomez regularly bring students to the MBL, where they are affiliated with the Program in Sensory Physiology and Behavior in addition to Cellular Dynamics.

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