Reciprocal epithelial-mesenchymal interactions are the key step in early tooth formation and defects in these interactions are likely to lead to tooth agenesis. Bone morphogenetic protein 4 (Bmp4), a crucial signal molecule in development of many tissues, is very likely required at early stages during tooth formation. Its spatial and temporal expression pattern correlates highly with the epithelial-mesenchymal interactions during initiation of tooth formation. Local application of recombinant Bmp4 to tooth buds in vitro can mimic the action of the dental epithelium during tooth induction. However, there is not direct in vivo evidence to show the importance of Bmp4 during tooth formation, since Bmp4 knockout mice die at an early stage of embryonic development prior to tooth development. Msx1 knockout mice have shown an early arrest of tooth formation, which is associated with substantial reduction of Bmp4 in arrested tooth germs. Addition of recombinant Bmp4 to Msx1-arrested tooth germs in vitro permits further tooth development (bud to cap stage). Previously, the applicants cloned the mouse Bmp4 gene and characterized its promoter. Msx homeobox binding sites were identified in the Bmp4 promoter. Msx expression plasmids up-regulate Bmp4 promoter activity in in vitro transfection assays. Using transgenic mice harboring lacZ gene driven by various Bmp4 promoter fragments, tooth- specific elements of BMp4 expression were narrowed down to the region between -1144 to -260 bp. Seven transgenic mouse lines with various expression levels of human Bmp4 cDNA have been generated.
The aim of this proposal is to investigate the role of Bmp4 and its regulation by Msx1 during normal and abnormal tooth formation in vivo. The underlying hypothesis for the proposed studies is that Msx1 acts upstream of Bmp4 at the transcriptional level and that Bmp4 is required for tooth formation. This will be tested by using transgenic mice and Msx1 knockout mice.
Specific Aim 1 will examine the expression changes of a luciferase or lacZ gene, driven by intact or specific Bmp4 promoter fragments, in the presence and absence of Msx1 to determine whether Msx1 can activate the Bmp4 in vivo.
Specific Aim 2 will examine whether overexpression of Bmp4 cDNA, driven by specific Msx1 promoter or the Bmp4 promoter fragments, can rescue the tooth formation defect in Msx1 knock out mice in vivo. This bypass experiment will address the regulatory roles of Msx1 on Bmp4, and examine roles of Bmp4 during tooth formation in vivo.
Specific Aim 3 will extend these animal experiments to examine potential mutations of the Msx1 gene in autosomal dominant forms of familial tooth agenesis. Research into this relatively unexplored area will contribute to our understanding of the basic Msx1- Bmp4 signal pathway, mechanisms of tooth formation, and possible cause of autosomal dominant forms of familial tooth agenesis.

Agency
National Institute of Health (NIH)
Institute
National Institute of Dental & Craniofacial Research (NIDCR)
Type
First Independent Research Support & Transition (FIRST) Awards (R29)
Project #
5R29DE013480-05
Application #
6628522
Study Section
Oral Biology and Medicine Subcommittee 1 (OBM)
Program Officer
Small, Rochelle K
Project Start
1999-02-01
Project End
2005-01-31
Budget Start
2003-02-01
Budget End
2005-01-31
Support Year
5
Fiscal Year
2003
Total Cost
$110,161
Indirect Cost
Name
University of Missouri Kansas City
Department
Dentistry
Type
Schools of Dentistry
DUNS #
010989619
City
Kansas City
State
MO
Country
United States
Zip Code
64110
Rios, H F; Ma, D; Xie, Y et al. (2008) Periostin is essential for the integrity and function of the periodontal ligament during occlusal loading in mice. J Periodontol 79:1480-90
Feng, Jian Q; Ward, Leanne M; Liu, Shiguang et al. (2006) Loss of DMP1 causes rickets and osteomalacia and identifies a role for osteocytes in mineral metabolism. Nat Genet 38:1310-5
Rios, Hector; Koushik, Shrinagesh V; Wang, Haiyan et al. (2005) periostin null mice exhibit dwarfism, incisor enamel defects, and an early-onset periodontal disease-like phenotype. Mol Cell Biol 25:11131-44
Ye, Ling; Mishina, Yuji; Chen, Di et al. (2005) Dmp1-deficient mice display severe defects in cartilage formation responsible for a chondrodysplasia-like phenotype. J Biol Chem 280:6197-203
Ye, Ling; MacDougall, Mary; Zhang, Shubin et al. (2004) Deletion of dentin matrix protein-1 leads to a partial failure of maturation of predentin into dentin, hypomineralization, and expanded cavities of pulp and root canal during postnatal tooth development. J Biol Chem 279:19141-8
Feng, Jian Q; Xing, Lianping; Zhang, Jiang-Hong et al. (2003) NF-kappaB specifically activates BMP-2 gene expression in growth plate chondrocytes in vivo and in a chondrocyte cell line in vitro. J Biol Chem 278:29130-5
Feng, J Q; Huang, H; Lu, Y et al. (2003) The Dentin matrix protein 1 (Dmp1) is specifically expressed in mineralized, but not soft, tissues during development. J Dent Res 82:776-80
Fen, Jian Q; Zhang, Jianghong; Dallas, Sarah L et al. (2002) Dentin matrix protein 1, a target molecule for Cbfa1 in bone, is a unique bone marker gene. J Bone Miner Res 17:1822-31
Zhang, Jianghong; Tan, Xiaoyu; Contag, Christopher H et al. (2002) Dissection of promoter control modules that direct Bmp4 expression in the epithelium-derived components of hair follicles. Biochem Biophys Res Commun 293:1412-9
Feng, J Q; Zhang, J; Tan, X et al. (2002) Identification of cis-DNA regions controlling Bmp4 expression during tooth morphogenesis in vivo. J Dent Res 81:6-10