MBL


By Laurel Hamers

One of the brain’s amazing abilities is self-repair: Although injury or illness may disrupt neural circuits, many connections will reform over time.

Artur Llobet, an MBL Research Awardee from the University of Barcelona, is spending his second consecutive summer in the Whitman Center for Visiting Research investigating olfactory neuron repair in Xenopus laevis, the African clawed frog.

Calcium labeling of olfactory sensory neurons' presynaptic terminals in a Xenopus laevis tadpole. Photo credit: Artur Llobet

Labelling of presynaptic terminals of olfactory sensory neurons in a Xenopus laevis tadpole using calcium green dextran. Image is pseudocolored so that yellow represents higher and blue lower calcium concentration.
Photo and caption: Artur Llobet

“One of the advantages of working with frogs is that they have fantastic regenerative capabilities,” says Llobet. Tadpoles are able to repair damaged neural circuits in a few days, making them ideal test subjects.

Llobet is working with a transgenic line of Xenopus tadpoles that express green fluorescent protein (GFP) in their neurons, allowing him to easily see the neural connections. Last year, he studied the timeframe of Xenopus neural repair by measuring how long snipped olfactory nerves took to regrow. Now, he is trying to understand in greater detail the mechanisms behind the repair process.

Neurons pass electrochemical messages between each other at junctions called synapses; when a neuron fires, the voltage change propagates along the nerve fiber (axon) and calcium increases at the presynaptic terminal, which releases neurotransmitters. By labeling the tadpoles’ synaptic terminals with calcium indicators, Llobet can visualize the functionality of the re-grown connections and determine when during the repair process the new synapses start signaling.

“In a GFP animal, we can see that the nerve has re-grown, but we don’t know if that nerve is actually working or not,” says Llobet. “So we look at the synapses and see whether the calcium concentration increases when we stimulate olfactory sensory neurons.” This calcium accumulation indicates that the new nerve is not just present, but also functional.

By examining neural repair in frogs, scientists hope to gain insight into this process in more complex systems such as the human brain.

Llobet’s research is taking place through the National Xenopus Resource (NXR) at the MBL, a center that maintains breeding stocks of frogs and provides training on advanced imaging and experimental technologies. According to Llobet, the specialized resources offered by the NXR make this research project possible. He is one of six MBL Research Awardees in 2014 to be using the animals and research services of the NXR, which is one of 28 National Institutes of Health-funded Animal Resource Centers nationwide and a cornerstone facility of the MBL’s Bell Center for Regenerative Biology and Tissue Engineering.

By Laurel Hamers

Our arms and legs normally work so fluidly that we may forget that their size and location were determined by complex genetic control during early development.

Keys to the precise regulatory ballet that makes our limbs look the way they do may be found in a seemingly dissimilar group of organisms: sharks and skates.

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Skates in the MBL’s Marine Resources Center. Photo credit: Laurel Hamers

Cartilaginous fish like sharks and skates are the oldest fish to have pectoral fins:  paired appendages that are the evolutionary predecessor of our arms. Tetsuya Nakamura, a postdoctoral researcher at the University of Chicago, is spending the summer at the MBL investigating these cartilaginous fish. He hopes to elucidate the molecular mechanisms responsible for the diversity of fin shapes in this single group of fish and, on a broader scale, the evolution of appendage shapes across species.

“The best way to understand the diversity of fin types is to study an extremely strange fish, like the skate,” says Nakamura. “The pectoral fins of skate are very wide—they’re totally different from other animals.”

Nakamura is focusing on Hox genes, which control body patterning during embryonic development; they are responsible, for example, for making sure your arms attach below your shoulders and not out the top of your head. Researchers can manipulate individual Hox genes and readily see structural differences in the body parts influenced by that gene.

By comparing expression patterns of Hox genes in the fins of skates and closely related sharks, Nakamura is identifying specific genes that may be responsible for the skate’s elongated pectoral fins compared to the shark’s narrower ones. He will then manipulate the expression of these genes in an attempt to alter fin shape.

The blue lines show the cartilage structure in the fins of two fish. Note the shark's narrow fins compared to the skate's wide, fan-like ones. Photo credit: Tetsuya Nakamura, composite image by Laurel Hamers

The blue lines show the cartilage structure in the fins of two fish. Note the shark’s narrow fins compared to the skate’s wide, fan-like ones. Photo credit: Tetsuya Nakamura, composite image by Laurel Hamers

“My opinion is that fin width is very important in deciding fin shape,” he says. “If I can control fin width, for example, to make narrower fin bases in skate, I think their fin shape would be like a shark’s.”

Nakamura, who is spending his first summer at MBL, is a member of Neil Shubin’s lab in the Department of Organismal Biology and Anatomy at UChicago.

A closeup of an Aedes aegypti mosquito biting its host. Photo credit: Alex Wild, alexanderwild.com

The yellow fever mosquito,  Aedes aegypti, biting its prey. Photo credit: Alex Wild, alexanderwild.com

By Laurel Hamers

It’s a question asked by many a summer stargazer: How do mosquitoes home in on their human prey, turning a relaxing evening into an itchy disaster?

Meg Younger, an MBL Grass Fellow and a postdoctoral scientist at Rockefeller University, is trying to find out by looking at mosquitoes’ neural responses to different combinations of odors.

Behavioral studies have identified several cues that are mildly attractive to mosquitoes: carbon dioxide, heat, and lactic acid, a component of sweat. Presented alone, none of these cues is particularly powerful; when paired together, however, their effects multiply.

“What we don’t know yet is how these stimuli that are ignored or only mildly attractive are transformed into very attractive stimuli in the brain when presented simultaneously,” Younger says.

Younger is using electrophysiology and calcium imaging to monitor olfactory neurons, looking for differences in brain activity when mosquitoes are presented with certain stimuli alone or in different combinations.

She is carrying out her research in the yellow fever mosquito, Aedes aegypti, which is found in tropical and subtropical areas and is the also the major vector for dengue fever and chikungunya.

“The more we know about how mosquitoes process different stimuli to find humans, the more potential we have to come up with creative ways to stop them from biting people and spreading diseases,” Younger says.

Male stolon (ventral view, anterior up) of the annelid, Proceraea sp., fluorescently stained for acetylated tubulin (green), serotonin (yellow), F-actin (red; phalloidin), and nuclei (blue; DAPI).  Confocal z-stacks were viewed as maximum  projections and tiled together to cover the entirety of the animal (body length approximately 7.5 mm).  By Eduardo Zattara (University of Maryland, College Park); Embryology Class of 2012.

Male stolon (ventral view, anterior up) of the annelid, Proceraea sp., fluorescently stained for acetylated tubulin (green), serotonin (yellow), F-actin (red; phalloidin), and nuclei (blue; DAPI). Confocal z-stacks were viewed as maximum projections and tiled together to cover the entirety of the animal (body length approximately 7.5 mm). By Eduardo Zattara (University of Maryland, College Park); Embryology class of 2012.

Angelo Iulianella, an assistant professor of medical neuroscience at Dalhousie University in Halifax, Nova Scotia, Canada, has assisted with the MBL’s Embryology class for the past six summers. He recently shared his experiences with the course on The Node, an online community for developmental biologists. Check out his post here!

Angelo Iulianella takes a break from work in the Embryology lab. (Photo credit: Laurel Hamers)

Angelo Iulianella takes a break from work in the Embryology lab. (Photo credit: Laurel Hamers)

 

The breadth and mysteries of Julie Huber’s research—from exploring the dark, peaceful ocean depths to mining enormous data sets about the microbes that live there—are captured in this video profile by Geoff Wyman of Falmouth. Huber describes her background growing up in the Midwest, and how her love for the ocean eventually led to a fascination with marine microbes and how they power the planet’s elemental cycles. Today, Huber dives to deep-sea environments around the world to collect samples of fluids from underwater volcanoes, which she analyzes back at the MBL to discover the microbial communities that can thrive under such extreme environmental conditions.

Huber is associate director of the MBL’s Josephine Bay Paul Center, and is also associate director of the National Science Foundation’s Center for Dark Energy Biosphere Investigations at the University of Southern California.

Many thanks to Geoff Wyman for producing this video, the first in a series of profiles of MBL scientists.

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