A study performed at the University of California, Los Angeles shows for the first time how microscopic crystals form sound and gravity sensors inside the inner ear. Located at the ends of cilia, these 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. Known as benign paroxysmal positional vertigo, the disorder plagues up to 10% of people older than 60 and causes 20% of patients’ dizziness complaints.
The researchers’ findings, published November 30 in the online edition of the journal Nature, suggest a potential gene target for the treatment of people suffering from common hearing 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," says Kent Hill, associate professor of microbiology, immunology, and molecular genetics at the David Geffen School of Medicine at UCLA and the UCLA 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 group of 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," Hill says. "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."
It has been suggested cilia movement contributes to the formation of ear crystals, but the idea had never been tested before, he says. "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."
Hill says the findings offer promise for the treatment of patients with hearing disorders and people with disorders marked by poor cilia function.
"The idea that physical movement can influence vertebrate development is very provocative," Hill says. "Scientists typically look at whether a particular gene is switched on or off, or if a particular protein is activated that determines if a tissue develops normally. In this case, microscopic currents in the fluid surrounding developing tissue are affecting its development. We need to understand more details of this process and determine how common it is during development."
Source: Elaine Schmidt; UCLA
[Source: Medical News Today]