Figure 2: Activity of Foxi3^GFP and Foxi3^CreER mice in the first and second pharyngeal arches.

(A-N): Expression of the Foxi3^GFP reporter in the first and second pharyngeal arches at E8.5, E9.5 and 10.5. Panels D, I and N illustrate the approximate planes of section for each panel at the three ages. (A-C) Foxi3^GFP is expressed in the ectoderm of the mandible and maxilla of the first pharyngeal arch (PA1) at E8.5, and in the pharyngeal cleft and pharyngeal pouch between the first and second arches (PC1 and PP1). (E-H) Foxi3^GFP expression begins to be down-regulated from the first arch ectoderm and endoderm by E9.5 but remains expressed in the cleft and pouch regions. Expression is also seen in the second and third cleft and pouch regions (PC2, PC3, PP2, PP3). (J-M) Foxi3^GFP continues to be down-regulated from the ectoderm of the first and second pharyngeal arches but persists in the first three cleft and pouch regions. (O-R). Foxi3^CreER mice were mated with ROSA-Ai9 Cre reporter mice and the pregnant females received a single dose of tamoxifen at 7.5 dpc. At E10.5, tdTomato-expressing cells can be observed in the ectoderm and endoderm of the first three cleft and pouch regions. Labeled cells can also be seen in the geniculate ganglion (VII, panel P), the otic vesicle (OV) and vestibulo-acoustic ganglion (VIII; panel Q) which are derived from Foxi3 lineage-labeled progenitors in the pre-placodal region.