SoxF is expressed early within the blastopore [(A & B) ventral view; E4.5] and the neural plate (C dorsal view). Beginning from E7 to E14, SoxF is expressed surrounding the notochord and in precursors to the thyroid, heart, and branchial arches (E–M). Beginning at E7, SoxF begins to express in the forming thyroid (L). Ventral view of E8.5 displaying the forming thyroid (G). In addition, SoxF is temporarily expressed in the first and second branchial arch at E14 and 16 (J and K). Bp: blastopore, NP: neural plate Th: thryroid precursors BA: Branchial Arch