A New Mexico State University professor is among a group of researchers that has co-authored an article about electric fish appearing in the latest edition of “Science” magazine.
Graciela Unguez, biology professor in the NMSU College of Arts and Sciences, and her graduate students Robert Guth and Matthew Pinch are contributors on the article “Genomic basis for the convergent evolution of electric organs,” which demonstrates how different types of electric fish came to form the cells of the organ that is specialized to generate electricity and give these fish their name. Some, like electric eels, can generate an electrical discharge of up to 600 volts, whereas others referred to as weakly electric fish generate charges of less than one volt – so low they cannot be felt by humans.
Unguez’s research team focuses on the commonly called yellow-stripe or long-tailed knife fish. The researchers are studying the evolution of the electric organ that produces the charge. Unguez explained that they want to understand the combination of genes that give rise to this extraordinary organ.
“These species of animals are very unique,” she said. “They’re the only ones that have a very specialized organ that generates electricity for the purposes of navigation, mate selection, communication, finding prey or self-defense. The ones we work with in our lab produce a very, very small charge; we can handle them very safely.”
Cells of the electric organ in all electric fishes come from the conversion of muscle cells, Unguez explained. However, because different species evolved separately and independently of each other in Africa and South America, whether the mechanism by which muscle cells change is the same across species is not known.
The study found that three of the four species examined turn off many of the muscle genes and turn on many genes that are commonly expressed in neurons. The yellow-stripe knife fish studied in the Unguez lab was the exception in that the electric organ continues to express most muscle genes even though it can no longer function as a muscle.
“It appears that the yellow-stripe knife fish is most likely one of the oldest species and used a different molecular approach to make an electric organ compared to the other three that evolved later,” said Unguez, whose area of interest is neuromuscular biology, the study of muscles and the nerves that innervate them.
NMSU researchers have shown that when the fish’s tail is cut off, it will regenerate. This includes its spinal cord, bone, artery, muscle and the electric organ. They’ve also observed that when input from the brain to the electric organ has been removed, the electric organ will revert back to muscle.
“The nervous system may be responsible for the conversion of muscle.” Unguez said. It is unknown what maintains the properties of mature cell types, but the group is using electric fish to begin manipulating different steps in the process of regeneration to answer this question.
Now, Unguez is in collaboration with researchers in the NMSU College of Engineering. After cutting the fish’s spinal cord, they will insert an electrode inside it to modify the electrical activity and observe whether there is a pattern that leads to the muscle conversion. She said the challenges of doing this kind of research are mostly technical since it has never been done. All the tools used to do this type of work have been optimized for animals – including humans – that live on land but not in water. Also, it’s difficult for the fish to breed in captivity, so she must depend on suppliers (yellow-stripe knife fish are native to the Amazon River).
Despite these minor obstacles, Unguez said she’s excited about the work and eager to see how it can be used to better understand muscle biology and disease in humans.
“We’re complementing these studies by culturing muscle cells from mice and exposing them to different stimulation patterns in a culture dish to see if we can make electric organs in the dish,” she said.
“This is a really exciting collaboration between many labs across the U.S.,” Unguez said about the “Science” article. “My students did a lot of work for this. Getting the co-authorship in such a high-profile journal with them is great. It shows how science is progressing – you have to collaborate with many people. This is an example of people with many different skills coming together to answer a question.”
The article is available at http://www.sciencemag.org/content/344/6191/1522.full.
Information from: NMSU