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The Mouse That Heard

By Sean Henahan, Access Excellence

Ann Arbor, MI (5/14/98)- A successful genetic repair job that restored hearing to the offspring of congenitally deaf mice could offer a new gene-therapy strategy for preventing deafness in humans.

Researchers at the University of Michigan first used transgenic technology to find the recessive mutated gene responsible for deafness in shaker-2 mice. This strain of mouse carries an X-ray induced mutation that causes deafness. The investigators then injected short sections of normal cloned DNA into fertilized mouse eggs to see which DNA clone would produce a hearing mouse. This enabled them to narrow their search for the mutant gene to a smaller area. Ultimately, they identified the single-point mutation on mouse chromosome 11. The normal gene and the shaker-2 gene were nearly identical except for one DNA base-pair out of more than 30,000 base-pairs in the gene.

This is the first permanent correction of a deafness-related genetic mutation and the fifth time that identification of a deafness gene in mice helped scientists find a similar gene in humans says Sally A. Camper, associate professor of human genetics in the University of Michigan Medical School, who directed the research (pictured).

The single-point mutation occurs in the area coding a gene for a key enzyme involved in inner ear development. The gene carries coding instructions for a previously unknown myosin enzyme, now dubbed Myo15.
The researchers believe that one function of this enzyme may be to transport a protein called actin to inner ear hair cell fibers during their development. These fibers, or stereocilia, move in response to changes in sound frequency, sending electrical signals to auditory nerves, which the brain translates into sound.

In related research, scientists at the National Institute on Deafness and Other Communication Disorders, National Institutes of Health, report finding a nearly identical gene (DFNB3) on human chromosome 17, which encodes the same type of myosin. Mutations in DFNB3 may produce congenital deafness in humans, just as mutations in shaker-2 do in mice.

"The next step is to develop delivery vehicles to introduce the normal gene into inner ear cells of individuals who carry these deafness genes," said Yehoash Raphael, assistant professor of otolaryngology in the U-M Medical School, who directed microscopy studies for the project. "Once adequate vectors are available, gene therapy for genetic-based deafness will become a reality."

Both research projects appear in the May 29, 1998  issue of Science. 

Related information on the Internet
Genetic Silencer
 Deafness Genes
 Hereditary Hearing Loss

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