Fig. 4. FGF8b represses midbrain development whereas FGF8a, FGF17b and FGF18 promote midbrain development. (A) Schematic diagram showing the in ovo electroporation experiments. DNA (green) is injected into the midbrain by a glass needle and five electric pulses are applied. DNA is driven toward the anode and transfected only on the right side of the brain, whereas the left side serves as an internal control. (B) Co-transfection of a GFP expression vector with the experimental vector serves to show that most cells on the right side of the brain, including the mid/hindbrain region and caudal forebrain, are transfected. (C) Dorsal view of a wild-type E10.5 chicken brain. (D) Dorsal view of an E10.5 chicken brain electroporated with 1µg/µl pMiw-Fgf8b; the asterisk indicates lack of midbrain (mes) on the transfected right side. (E) Dorsal view of an E6.5 chicken brain electroporated with 1 µg/µl pMiw-Fgf8a; the midbrain on the transfected side is larger than the one on the control side. (F) Dorsal view of an E8.5 chicken brain electroporated with 1 µg/µl pMiw-Fgf17b; the midbrain on the transfected side is larger than the one on the control side. (G) Dorsal view of an E8.5 chicken brain electroporated with 1 µg/µl pMiw-Fgf18; the midbrain on the transfected side is larger than the one on the control side. tel, telencephalon; di, diencephlon; mes, mesencephalon; ce, cerebellum.