February 26, 2009
Scientists Identify Gene Responsible For Tooth Growth
Scientists have reported new insights gathered from a single gene that could one day be used to help adults grow a new set of teeth.
Scientists from the University of Rochester bred mice that lacked the oddskipped related-2 (Osr2) gene. They noted that mice that lacked the gene grew an extra set of teeth next to their molars in similar fashion to sharks and other non-mammals.
"It's exciting. We've got a clue what to do," Dr. Songtao Shi of the University of Southern California School of Dentistry told the AP.
US adults over the age of 20 lack an average of four teeth, researchers said. When adult teeth are lost, they do not grow back. Current tooth replacement efforts involve dentures or dental implants.
Teeth begin to form in humans during early development from the epithelium and mesenchyme tissue layers. Scientists had previously assumed that epithelial cells within the dental lamina were responsible for tooth formation.
However, they found that tooth formation actually occurs within the deeper cell layer of the mesenchyme. The Osr2 gene works with two other genes to create teeth in specific locations, said Rulang Jiang, Ph.D., associate professor of Biomedical Genetics in the Center for Oral Biology at the University of Rochester Medical Center.
"This finding was exciting because extra teeth developed from tissue that normally does not give rise to teeth," said Jiang.
"It takes the concerted actions of hundreds of genes to build a tooth, so it was amazing to find that deleting one gene caused the activation of a complete tooth developmental program outside of the normal tooth row in those mice. Finding out how the extra teeth developed will reveal how nature makes a tooth from scratch, which will guide tooth regeneration research."
"It's almost a self-generating propagation of the signal" that leads to one tooth after another forming all in a row, he said.
In addition to learning more about how tooth growth occurs, Jiang's team also discovered some of the biochemical pathways involved in cleft lip/cleft palate development. This process may include BMP4, Msx1 and OSR2 as well as several others. In humans, Msx1 mutations have been linked with cleft lip/palate and with the failure to develop one or more teeth.
Researchers now plan to look at what other factors may be regulated by Msx1 and Osr2 to begin pinpointing the genetic network that controls teeth patterning and palate development. They hope to be able to develop stem cell treatments to develop prevention strategies for cleft palate.
"Beyond medical applications, our results suggest that diversity in the number of tooth rows across species may be due to evolutionary changes in the control of the BMP4/Msx1 pathway," Jiang said. "In mammals, Osr2 suppresses this pathway to restrict teeth within a single row."
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