Fig. 6.

Upregulation of FGF signalling activity in the neural plate border region is responsible for the absence of pineal progenitors in otxH morphant embryos. (A-B′) Representative images of dual colour in situ hybridisation for erm (blue) and flh (red) in wild-type (n=29; A,A′) and otxH (n=32; B,B′) bud stage zebrafish embryos; anterior is leftwards. (A′,B′) The boxed neural plate border region in A,B in more detail. (C-H) Wild-type (C,E,G) and otxH morphant (D,F,H) zebrafish embryos stained for fgf8 (red) and otx5 (blue) at 24 hpf (anterior is leftwards, dorsal towards the top; C,D, n=18). Embryos in E,F were treated with the FGF inhibitor SU5402 (n=25 and n=22, respectively). Embryos in G,H are transgenic for a heat shock-inducible dominant-negative FGF receptor and were heat-shocked at shield stage (n=19 and n=22, respectively). otx5-positive pineal progenitors are rescued by pharmacological inhibition of FGF signalling in F and by heat shock-induced receptor inhibition in H (compare with D). Inset in H shows a sibling from the Tg(hsp:dnfgfr1) cross that did not show rescue and is therefore likely to be from the 25% of offspring that are expected to be negative for the transgene. Results are based on two independent experiments. Scale bar: 50 µm.