Scientists Discover Why Teeth Form in a ...(ecial quality of epithelial cells there ...),Health

Date:2/26/2009

ecial quality of epithelial cells there made them "tooth competent." Classical experiments, however, found that the developing tooth mesenchyme was capable of inducing tooth formation from epithelial tissues that normally would not participate in tooth development. Researchers confirmed that it was indeed the mesenchyme that carried tooth initiation signals later in development, but how those signals were restricted to the area beneath the tooth row was unknown.

Past studies in other labs had shown bone morphogenic protein 4 (BMP4) to be an important factor for the initiation of teeth, and that a protein called Msx1 amplifies the BMP4 tooth-generating signal. Jiang and colleagues suggested for the first time that some unknown factor was restricting the growth of teeth into one row by opposing the Bmp4 signal.

The current study provides the first solid proof that the precise space where mammals can develop teeth (the "tooth morphogenetic field") is shaped and restricted by the effect of Osr2 on the expression of the Bmp4 gene within the mesenchymal cell layer. Jiang's team has shown not only that removing the Osr2 gene results in extra teeth outside of the normal row, but also that Osr2 is expressed in increasing concentration in the jaw mesenchyme as you move from the cheek toward the tongue in the mouse embryo, the exact opposite of the BMP4 concentration gradient. Osr2 restricts Bmp4 expression to the tooth mesenchyme under the dental lamina, and in Osr2's absence, Bmp4 gene expression expands into the jaw mesenchyme outside of the tooth row.

A second major finding of the study backs up another emerging theory which holds that careful regulation of competing pro- and anti-tooth initiation signals controls how mammalian teeth come one by one in sequence. As each tooth develops, something must prevent it from forming too close to the next or mammals would have no gaps between their teeth. When this mechanism occas
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SOURCE University of Rochester Medical Center Copyright©2009 PR Newswire. All rights reserved

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