Fig. 5. Epibranchial development is modulated by FGF signalling. (A) Chick Foxi2 is normally excluded from the presumptive otic region. (B) Downregulation of Fgf3 and Fgf19 expression following electroporation of shFgf causes a downregulation of Foxi2 expression (n=16/29). (C)pEF-Fgf electroporation results in stronger Foxi2 expression, although it remains excluded from the otic domain (n=11/25). (D) Frozen sections of double in situ hybridisations showing the region of overlap between Pax2 (green) and Foxi2 (red). (E) The region of overlap is reduced or absent when FGF expression is suppressed. (F) FGF overexpression increases the region of Pax2/Foxi2 overlap. (G) At the 20ss of chick development, Pax2 normally segregates into epibranchial and otic expression domains. (H) Downregulation of Fgf3 and Fgf19 results in the reduction of both otic and epibranchial Pax2 domains at 20ss. (I) Sustained FGF expression causes stronger Pax2 expression in both otic and epibranchial domains. (J) By 27ss, epibranchial precursors undergo neurogenesis, forming Phox2b-positive neuroblasts. (K) Epibranchial neurogenesis, as marked by Phox2b expression, is suppressed in shFgf electroporated embryos (n=9/15). (L) In pEF-Fgf electroporated embryos, the Phox2b expression domain is expanded (n=6/9). In all panels the electroporated side is to the right.