About 75% of birth defects involve the head, face, and oral tissues. Although orofacial clefts and other craniofacial malformations have clear environmental and genetic causes, insufficient information exists concerning the mechanisms of craniofacial development to enable the majority of these defects to be detected or prevented pre-natally. Our goal is to develop animal models of craniofacial malformations that will lead to mechanistic insight into the diagnosis and treatment of related human birth defects. We focus on the AP-2 family of transcription factors since these genes provide a link between the genetic and environmental causes of human birth defects affecting the face. In mouse and human, five separate genes encode the various AP-2 proteins. Three of these genes are expressed in the developing mouse face, Tcfap2a, Tcfap2b, and Tcfap2c encoding the proteins AP-2a, AP-2?, and AP-2? respectively. The human gene encoding AP-2a is mutated in Branchio-Oculo-Facial Syndrome (BOFS) in which there are orofacial clefting defects. Similarly, mutations in the human gene encoding AP-2? cause Char syndrome, which is characterized by face, heart, and limb defects. Expression of Tcfap2a and Tcfap2c are also responsive to retinoic acid application both in vitro and in vivo and these genes form an important component of the gene regulatory network affected by this powerful teratogen. Single gene knockouts of the three mouse AP-2 genes discussed above all result in death during embryogenesis or soon after birth. Tcfap2b null mice do not display overt facial defects and die due to neurological and kidney problems. Tcfap2c null mice die during gastrulation, and so it has been more difficult to gauge the role of this gene in face formation. Tcfap2a has the most direct link to craniofacial development. The Tcfap2a null embryos display multiple defects including orofacial clefting and hypoplasia of the neural crest derived facial skeleton and this is mainly due to loss of AP-2a function in the surface ectoderm. Although Tcfap2a, Tcfap2b, and Tcfap2c have unique roles in development, recent data show that they also share redundant functions. Indeed, preliminary studies indicate that the facial phenotypes generated by compound knockouts of these genes are far more serious than the individual gene knockouts. Thus, the goal of this application is to determine how these proteins function together to regulate craniofacial formation.
In Aim 1, we will generate a mouse model of BOFS, which we hypothesize inhibits AP-2 function via a dominant negative mechanism.
In Aims 2 and 3 we will generate and analyze particular knockout combinations of the three AP-2 genes expressed in the face using tissue specific Cre-LoxP technology. The results of these analyses will reveal the combinatorial roles for the AP-2 genes in craniofacial morphogenesis and provide significant insight into the transcriptional control of facial development.

Public Health Relevance

Birth defects affect ~ 3% of all infants born in the US - with about 75% of these involving the head, face, and oral tissues - and the presence of a major birth defect will frequently reduce the quality of life for both the child and the parents. Insufficient information exists concerning the mechanisms of craniofacial development to enable the majority of these defects to be detected or prevented pre-natally. We are using animal model systems to determine how normal and abnormal craniofacial development proceeds and to identify new mechanisms that mediate face formation so that we may apply this knowledge to understand and ultimately treat the origins of human facial birth defects.

Agency
National Institute of Health (NIH)
Institute
National Institute of Dental & Craniofacial Research (NIDCR)
Type
Research Project (R01)
Project #
5R01DE012728-16
Application #
8448024
Study Section
Skeletal Biology Development and Disease Study Section (SBDD)
Program Officer
Scholnick, Steven
Project Start
1998-08-01
Project End
2014-03-31
Budget Start
2013-04-01
Budget End
2014-03-31
Support Year
16
Fiscal Year
2013
Total Cost
$367,152
Indirect Cost
$114,433
Name
University of Colorado Denver
Department
Dentistry
Type
Schools of Dentistry
DUNS #
041096314
City
Aurora
State
CO
Country
United States
Zip Code
80045
Kurosaka, Hiroshi; Iulianella, Angelo; Williams, Trevor et al. (2014) Disrupting hedgehog and WNT signaling interactions promotes cleft lip pathogenesis. J Clin Invest 124:1660-71
Hooper, Joan E (2014) A survey of software for genome-wide discovery of differential splicing in RNA-Seq data. Hum Genomics 8:3
Li, Hong; Williams, Trevor (2013) Separation of mouse embryonic facial ectoderm and mesenchyme. J Vis Exp :
Wang, Jun; Bai, Yan; Li, Hong et al. (2013) MicroRNA-17-92, a direct Ap-2* transcriptional target, modulates T-box factor activity in orofacial clefting. PLoS Genet 9:e1003785
Li, Hong; Sheridan, Ryan; Williams, Trevor (2013) Analysis of TFAP2A mutations in Branchio-Oculo-Facial Syndrome indicates functional complexity within the AP-2* DNA-binding domain. Hum Mol Genet 22:3195-206
Bassett, Erin A; Korol, Anna; Deschamps, Paula A et al. (2012) Overlapping expression patterns and redundant roles for AP-2 transcription factors in the developing mammalian retina. Dev Dyn 241:814-29
Kerr, Christine L; Huang, Jian; Williams, Trevor et al. (2012) Activation of the hedgehog signaling pathway in the developing lens stimulates ectopic FoxE3 expression and disruption in fiber cell differentiation. Invest Ophthalmol Vis Sci 53:3316-30
Harlow, Danielle E; Yang, Hui; Williams, Trevor et al. (2011) Epibranchial placode-derived neurons produce BDNF required for early sensory neuron development. Dev Dyn 240:309-23
Forni, Paolo Emanuele; Taylor-Burds, Carol; Melvin, Vida Senkus et al. (2011) Neural crest and ectodermal cells intermix in the nasal placode to give rise to GnRH-1 neurons, sensory neurons, and olfactory ensheathing cells. J Neurosci 31:6915-27
Bassett, Erin A; Williams, Trevor; Zacharias, Amanda L et al. (2010) AP-2alpha knockout mice exhibit optic cup patterning defects and failure of optic stalk morphogenesis. Hum Mol Genet 19:1791-804

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