A UCLA study shows for the first time how microscopic crystals form sound and gravity sensors inside the inner ear.
Located at the ends of cilia - tiny cellular hairs in the ear that move and transmit signals -- the crystals play an important role in detecting sound, maintaining balance and regulating movement.
Dislodged ear crystals are to blame for the most common form of vertigo. Called benign paroxysmal positional vertigo, the disorder plagues up to 10 percent of people older than 60 and causes 20 percent of patients' dizziness complaints.
Published Nov. 30 in the advance online edition of Nature , the UCLA findings suggest a potential gene target for the treatment of people suffering from common hearing, vertigo and balance problems related to cilia disorders.
"People have known for a long time about the importance of cilia for propelling sperm up the uterus and moving mucus out of the lungs," explained Kent Hill, associate professor of microbiology, immunology and molecular genetics at UCLA's David Geffen School of Medicine and College of Letters and Science. "Our study illustrates that cilia perform many additional jobs that are essential to how our bodies develop and work."
Hill's team employed high-speed, high-definition video imaging to watch cilia moving in real time inside the developing ears of embryonic zebrafish. These small bony fish undergo stages of development similar to humans and other vertebrates, making them useful models for research.
The researchers labeled cilia in the fish with fluorescent probes and used video microscopy to visualize the cilia and other inner ear structures. In the control fish, long cilia beat like tiny oars, causing tiny particles to circle in a vortex around them. The tornado of whirling particles accumulated at the proper location to form the inner ear's crystalline sensors.
"We next blocked expression of a gene that controls dynein -- a tiny molecular motor that drives cilia movement," said Hill. "When we examined the embryos, we saw that cilia movement came to a halt. As a result, the particles did not assemble in the correct site. So not only did ear crystals form in the wrong place, but they were misshapen and abnormally sized."
"While it's been suggested that cilia movement contributes to the formation of ear crystals, this idea had never been tested before," he added. "Our findings show that cilia in the ear do move and demonstrate that cilia movement is needed for ear crystals to assemble in the right place."