Foxi3^GFP and Foxi3^CreER mice allow identification and lineage labeling of pharyngeal arch ectoderm and endoderm, and tooth and hair placodes

Background: FOXI3 is a forkhead family transcription factor that is expressed in the progenitors of craniofacial placodes, epidermal placodes, and the ectoderm and endoderm of the pharyngeal arch region. Loss of Foxi3 in mice and pathogenic Foxi3 variants in dogs and humans cause a variety of craniofacial defects including absence of the inner ear, severe truncations of the jaw, loss or reduction in external and middle ear structures, and defects in teeth and hair. Results: To allow for the identification, isolation, and lineage tracing of Foxi3-expressing cells in developing mice, we targeted the Foxi3 locus to create Foxi3^GFP and Foxi3^CreER mice. We show that Foxi3^GFP mice faithfully recapitulate the expression pattern of Foxi3 mRNA at all ages examined, and Foxi3^CreER mice can trace the derivatives of pharyngeal arch ectoderm and endoderm, the pharyngeal pouches and clefts that separate each arch, and the derivatives of hair and tooth placodes. Conclusions: Foxi3^GFP and Foxi3^CreER mice are new tools that will be of use in identifying and manipulating pharyngeal arch ectoderm and endoderm and hair and tooth placodes.