Transparent Models
Zebrafish Help Scientists See How Hearing Works
A small, striped fish that’s found in pet stores across the country has become an important animal model for hearing and balance research, said Dr. Katie Kindt, during the recent National Institute on Deafness and Other Communication Disorders (NIDCD) “Beyond the Lab: Understanding Communication Disorders” speaker series lecture.
“Zebrafish are great for studying development,” said Kindt, senior investigator in NIDCD’s section on sensory cell development and function. “We can use modern tools to see what’s happening to hearing in a living animal.”
Most of the research her lab conducts takes place in zebrafish embryos and newly hatched larvae. That’s because zebrafish are transparent at very young ages.
“We can watch each and every cell division and every morphological event that happens as an embryo develops,” she said.
Zebrafish are a particularly useful model for hearing and balance research because of their transparency. Scientists can study the development of sensory cells of the inner ear in zebrafish in real-time.
Called hair cells because of hair-like structures located on top of each cell, these sensory cells detect sound and help maintain balance. Special connections called ribbons sit at the bottom of each hair cell. These ribbons can be lost due to loud nose, aging or ear-toxic drugs. The loss of these connections disrupts sound signaling to the brain, ultimately leading to hearing loss.
“What’s also really powerful about being a transparent animal is that we can use really cool tools for our research,” Kindt said. “One of those is green fluorescent protein, or GFP.”
Originally identified in jellyfish, GFP glows fluorescent green when exposed to blue light. GFP can be introduced into zebrafish. Kindt’s lab genetically engineers zebrafish with GFP in hair cells. This approach helps them see every hair cell.
Experiments like these are impossible in humans and other mammals. That’s because hair cells are embedded in one of the body’s densest bones. There is no way to study these cells without removing the ear.
The fish have hair cells in two places: in their ear and down the side of their body. The hair cells in their ear are used for hearing and for balance. The hair cells that run down the side of their body are part of the lateral-line system. Lateral line hair cells are directly on the fish’s skin. These cells help zebrafish to sense local water movement.
“It’s important for a lot of behaviors for fish, like breeding, prey detection and predator avoidance,” she said. “Some fish use their lateral line for a behavior called schooling.”
Currently, her lab is studying how the ribbons at the bottom of the hair cell form connections to the brain in zebrafish. By understanding how these connections form normally, “we can understand how to reform them after they are lost in cases of hearing loss.”
Dr. Saman Hussain, a scientist in Kindt’s lab, recorded the development process using video technology.
In young hair cells, tiny ribbons are at the top of a hair cell. As the cell matures, ribbons move from the top to the bottom on cellular highways called microtubules. During their migration, the ribbons fuse together to create larger ribbons.
“By using movies, we’re able to tell the whole story and piece together what’s happening during this developmental process,” Kindt concluded. “We might’ve been able to guess this process, but seeing is believing in development. We’re scientists, we can’t guess. We have to know what happens.”
To watch the lecture in full, visit https://videocast.nih.gov/watch=54530.