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First published online 12 December 2007
doi: 10.1242/dev.015081
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1 Department of Anatomy and Program in Developmental Biology, School of
Medicine, University of California at San Francisco, San Francisco, CA
94143-2711, USA.
2 Department of Pediatrics, School of Medicine, University of California at San
Francisco, San Francisco, CA 94143-2711, USA.
3 Department of Orofacial Sciences, School of Dentistry, University of
California at San Francisco, San Francisco, CA 94143-0758, USA.
4 Department of Preventive and Restorative Dental Sciences, School of Dentistry,
University of California at San Francisco, San Francisco, CA 94143-0758,
USA.
5 Department of Craniofacial Development, King's College London, London, SE1
9RT, UK.
6 Department of Teratology, Institute of Experimental Medicine, Academy of
Sciences of the Czech Republic, Prague, Czech Republic.
* Author for correspondence (e-mail: gail.r.martin{at}ucsf.edu)
Accepted 14 October 2007
Rodent incisors grow throughout adult life, but are prevented from becoming excessively long by constant abrasion, which is facilitated by the absence of enamel on one side of the incisor. Here we report that loss-of-function of sprouty genes, which encode antagonists of receptor tyrosine kinase signaling, leads to bilateral enamel deposition, thus impeding incisor abrasion and resulting in unchecked tooth elongation. We demonstrate that sprouty genes function to ensure that enamel-producing ameloblasts are generated on only one side of the tooth by inhibiting the formation of ectopic ameloblasts from self-renewing stem cells, and that they do so by preventing the establishment of an epithelial-mesenchymal FGF signaling loop. Interestingly, although inactivation of Spry4 alone initiates ectopic ameloblast formation in the embryo, the dosage of another sprouty gene must also be reduced to sustain it after birth. These data reveal that the generation of differentiated progeny from a particular stem cell population can be differently regulated in the embryo and adult.
Key words: Ameloblast, Enamel, FGF signaling, Sprouty genes, Stem cells
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