Briefly, specific research interests include the role of signaling molecules involved in epithelial-mesenchymal interactions in tooth and bone development; Genetic etiology of tooth agenesis; Molecular control of odontoblast differentiation and the use of tooth-derived stem cells for regeneration of the dentin-pulp complex and periodontium.  A detailed description of our current projects follows:

The roles of Runx2 and Twist-1 in tooth morphogenesis

Mammals, including humans and rodents, develop a specific number of tooth in a single row along the long axis of each jaw quadrant.  This tooth morphogenesis and patterning is tightly controlled by several signaling molecules, as well as many transcription factors.  The known signaling molecules include members of transforming growth factor β (TGFβ), fibroblast growth factor (FGF), sonic hedgehog (Shh), Wnt and tumor necrosis factor (TNF).  The transcription factors involved include Msx1, Pax 9, Osr2, Runx2 and Twist-1, etc.  These signaling molecules and transcription factors mediate the sequential interactions between and within epithelial and mesenchymal tissues by regulating the expression of signaling receptors, new signaling molecules and other transcription factors. Any disturbance in the signaling pathway or mutations in transcription factors will result in either supernumerary teeth or tooth agenesis.

In this project, we mainly focus on two transcription factors to study their roles in tooth morphogenesis: Runx2 and Twist-1, which have been shown to have antagonistic functions in osteoblast differentiation.  Runx2 is a transcription factor with homology to the Drosophila pair-rule gene runt.  Runx2 mutations in humans result in autosomal-dominant cleido-cranial dysplasia (CCD), characterized by dysplastic clavicles, patent sutures and fontanelles and supernumerary teeth.  Runx2 mutant mice develop molars arrested at the late bud stage.  Twist-1 is a basic-helix-loop-helix (bHLH) containing transcription factor.  Twist-1 mutations in humans cause Saethre-Chotzen Syndrome (SCS), which shows an overlapping phenotype with mutations in the FGFR3 or FGFR2 genes.  The hallmark features of the disorder are craniosynostoses, syndactyly of the fingers, duplicated halluces, and facial asymmetry.   Dental anomalies reported in SCS include multiple hypoplastic, peg-shaped incisors and tooth agenesis, as well as pulp stone seen in teeth with broad, bulbous crowns and narrow, tapering roots.

Our goal is to understand the molecular mechanisms underlying the supernumerary teeth produced in CCD patients and tooth agenesis in Runx2 mutant mice. Specifically, we study the antagonistic role of Twist-1 on Runx2 in tooth morphogenesis, using both molecular and genetic approaches described as follows: 1) To determine whether Twist-1 also exerts the same antagonistic function on Runx2 in odontoblst differentiation, using lentivirus-mediated overexpression or silencing of Runx2 and Twist-1 in dental pulp stem cells (DPSC); 2) To perform a genetic rescue study by generating compound mutants that completely lack Runx2 and are also heterozygous for Twist-1 genes, and to determine whether lower Twist-1 activity will rescue the tooth defects in Runx2 mutants; and 3) To study how Runx2 and Twist-1 are integrated into the known signaling pathways to regulate tooth morphogenesis using both in vitro and in vivo approaches.

Signaling mechanisms in early tooth development

Our research in this area focuses on the elaboration of the interaction between transcription factors Pax9 and Msx1 and signaling protein Bmp4 in the mesenchymal layer of the tooth bud.  The paired domain transcription factor Pax9 and the homeodomain transcription factor Msx1 are of special interest because mutations in either gene cause severe tooth agenesis in humans.  The products of both genes are also necessary for the induction of the TGFβ superfamily member bone morphogenetic protein Bmp4.  Bmp4 is the critical signaling factor for progression of the bud stage to the cap stage of odontogenesis.  Specifically our goals are:

1)  To define the molecular relationship between Pax9, Msx1 and Bmp4 and other partner genes that leads to the progression of tooth bud development.  This research involves mapping the protein-protein interaction domains of Pax9 and Msx1, delineating regulatory sequences within the Msx1 and Bmp4 promoters, performing a functional analysis of naturally occurring PAX9 mutant proteins, identification of other Pax9-interacting proteins and of Pax9-dependent genes.  We also intend to clarify mechanism(s) of Bmp4 induction by Msx1.

2) To identify new tooth agenesis and Pax9/Msx1 partner genes through genetic studies of patients with familial tooth agenesis.  Here we will continue to pursue a high throughput candidate sequencing approach.  We will also add association studies for the evaluation of common sequence variants in hypodontia.  Gene detection through linkage analysis will be attempted in large enough families.

Recent Grants

• Nanostructured Peptide Hydrogels and Stem Cells for Dentin-Pulp Complex Regeneration. IADR/GlaxoSmithKline Innovation in Oral Care Awards, 2009-2011.
• Signaling Mechanisms in Early Tooth Development.  NIH 5 R01 DE019471, 2008-2012.

          - ARRA Administrative Collaborative Supplement, 2009-2011

• Regulation of Runx2 Function by Twist-1 in Tooth Development. NIH R01 DE13368, 2006-2010

• Baylor's Program for Bioengineering Sciences and Translational Research: B-BEST.  NIH 1 P30 DE020742-01, 2009-2011
• Baylor's Scientific Training Program for Dental Academic Researchers: B-STARS. NIH 5 T32 DE018380, 2008-2012
• Self-assembling Peptide-amphiphile Nanofibers as a Scaffold for Dental Stem Cells. Alliance for Nano Health Seed Grant; 2006-2009