Regulation of Tbx22 During Zebrafish Pharyngeal Arch Development

Mutations in human TBX22 cause X-linked cleft palate with anklyoglossia syndrome. The two zebrafish tbx22 splice isoforms, tbx22a and tbx22b, encode proteins of 444 and 400 amino acids, respectively. Tbx22a resembles canonical Tbx22 orthologs, while tbx22b lacks conserved N-terminal sequence. Zebrafish Tbx22 mRNA expression mirrors mammalian tbx22 expression and is consistent with early patterning of the vertebrate face. In zebrafish, tbx22 mRNA is strongly expressed in ectomesenchymal cells underlying the stomodeum, a bilaminar epithelial structure demarcating the early forming mouth and therefore, is hypothesized to be involved in jaw development. Objectives: the goal of this work is to determine the role of each form of tbx22 in jaw formation and to characterize regulatory elements that control the expression of tbx22 in the developing mouth. Methods: Morpholino technology was used to knockdown tbx22a or tbx22b expression in zebrafish and Alcian Blue staining was used to analyze developing cartilages in tbx22-MO injected zebrafish embryos. GFP reporter constructs were generated to determine promoter regions that drive localization of tbx22 to the specific bilateral  domains during early mouth formation. Results: Defects in tbx22a or tbx22b signaling cause ventral displacement of cartilages and joint defects with loss of tbx22b causing an overall more severe developmental defect. Conclusion: Our results demonstrate that tbx22 is necessary for proper dorsal ventral positioning of pharyngeal arches, and joint formation in zebrafish, and that GFP reporter constructs reveal essential regulatory elements upstream of the tbx22a start site. Supported by NIDCR grant K22 DE14683, 1R15DE019723 and UMD Healey Foundation Award to TLF.