Functional Characterization of Mediator Complex Proteins in Neural Crest and Craniofacial Development - PROJECT SUMMARY
Craniofacial developmental disorders such as cleft palate and retrognathia (smaller lower jaw) often arise due to
defects in neural crest cell development and affect 1 in 700 and 1 in 1,500 live human births, respectively. Cleft
palate and retrognathia often present with other craniofacial anomalies in conditions such as Treacher Collins
syndrome and DiGeorge syndrome. Although genetic analyses have identified the genes responsible for some
craniofacial anomalies, the vast majority have an undiagnosed molecular etiology and cellular pathogenesis. In
an ENU mutagenesis screen, the Med23 gene was identified to be critical for craniofacial development. A point
mutation in Med23 results in craniofacial and vascular defects, leading to embryonic lethality at mid-gestation.
Med23 belongs to the tail module of the Mediator complex, which is a global transcription coregulator for genes
transcribed by RNA Polymerase II. Med23 is ubiquitously expressed in mouse embryos, thereby, raising an
important question of how a ubiquitously expressed protein regulates tissue specific development during
embryogenesis, particularly in craniofacial development. To understand the function of Med23 in craniofacial
and neural crest cell development, I generated neural crest cell specific conditional knockouts of Med23 that
exhibit cleft palate, retrognathia, glossoptosis and cleidocranial dysplasia. Interestingly, endothelial cell specific
conditional knockouts of Med23 also result in craniofacial defects together with vascular defects. In this proposal,
I will test the overarching hypothesis that Med23 and other tail module subunits of Mediator have important and
distinct transcriptional regulatory functions in craniofacial development via the control of neural crest cell and
endothelial cell transcriptomes. Specifically, I will address the following aims. (Aim 1) Identify the molecular
mechanism underlying the craniofacial defect in neural crest cell specific mutants of Med23 by analyzing
transcriptomic changes in these mutants as well as by identifying Med23 DNA and protein binding partners. (Aim
2) Characterize the pathogenesis of craniofacial defects in endothelial cell specific mutants of Med23 and their
underlying molecular mechanisms by analysis of the craniofacial transcriptome. Furthermore, I will test the
mechanism of Med23-mediated control of key regulatory genes that function in craniofacial development and
are linked to craniofacial disorders. Specifically, I will investigate the molecular basis of Med23 function via its
control of Runx2 and β-Catenin in the mandibular mesenchyme. (Aim 3) Generate and characterize loss of
function mutants of the Mediator tail submodule protein, Med24. The broad impact of this innovative proposal
will advance our mechanistic understanding of the gene and protein networks underlying the function of global
transcription co-factor Mediator complex proteins in fundamental cellular processes and development.
