Abstract
Hemifacial microsomia (HFM) spans an array of human congenital craniofacial birth defect syndromes
characterized by asymmetric malformation or underdevelopment of the orbits (maxilla and zygoma),
mandible, outer and middle ear structures, craniofacial nerves and soft tissue structures. These elements
are derived from cranial neural crest cells (NCCs) that populate the pharyngeal arches. HFM is the second
most common facial birth defect behind cleft palate, though unlike cleft palate, very few genes have a
proven association with HFM. One of the few genes found repeatedly in GWAS studies is the transcription
factor GATA3, which is the basis of this proposal.
We have recently shown that GATA3 is required for facial symmetry, as Gata3 mutant mouse
embryos develop craniofacial defects resembling those seen in HFM, with one side more severely affected
than the other. However, our preliminary data show that while Gata3 mutant mouse embryos have several
changes in pharyngeal arch gene regulatory networks (GRNs), including expansion of Bmp4 expression
and reduction in Fgf8 expression, these changes are bilateral. Further, it is not clear if these represent
primary or secondary changes to GRNs and whether defects occur in NCCs before they reach the
pharyngeal arches. We hypothesize that GATA3 is required for two specific aspects of facial development:
1) to ensure sufficient migrating NCCs reach the first arch; and 2) to repress Bmp4 expression in the arch
ectoderm after NCC migration that would otherwise drive down Fgf8 expression and result in asymmetric
jaw morphogenesis.
To address these hypotheses, we will pursue three specific aims. In Aim 1, we will perform a detailed
analysis of NCC migration, proliferation/cell death and later differentiation in Gata3 mutants. We will also
assess if disruption of internal organ asymmetry randomizes sided defects in Gata3 mutants. In Aim 2, we will
perform dual scRNA-seq/scATAC-seq (scMultiome) in wild type and Gata3 mutants to identify symmetric and
asymmetric changes in gene expression. We will correlate this with chromatin accessibility changes and
functionally analyze identified putative cis-regulatory elements in vivo. In Aim 3, we will reduce Bmpr1a
expression or increase Fgf8 expression in the mandibular arch of Gata3 mutant embryos to determine if either
approach can rescue the Gata3 mutant phenotype.
Our long-term goal is to elucidate the basis of facial defects in the Gata3 mutant embryos and to
identify the cue or cues that result in asymmetry. Such an understanding has the potential to substantially
impact the quality of care for HFM patients and may potentially lead to avenues for future treatment
regimens designed to improve differences associated with HFM.