Expression of er81 during zebrafish embryogenesis. By wholemount in situ hybridisation, er81 expression is first detected at 16 hours post-fertilisation (hpf) in the anlage of the lens placodes (A). At 22 hpf (B and C), er81 transcripts are still seen in the lens placodes; however expression now appears in the prospective dorsal telencephalon and in the trigeminal ganglion (double arrowheads). At 28 hpf (D–F), expression remains in the dorsal telencephalon and trigeminal ganglia but is also detected in the ventral telencephalon and in a group of cells located at an intermediate dorsoventral position in the diencephalon (arrows in E and F). At 48 hpf (G–I) and 72 hpf (J–L), expression of er81 remains strong in the telencephalon but is also detected in the habenular nuclei (arrowheads in G and H, K and L) and in dispersed cells of the dorsal tectum. Expression in discreet neurons in the rhombencephalon is also detected at 72 h hpf (double arrows in L); the cloaca in indicated in (J) by an asterisk. (B, D and E, H, J and K) represent lateral views whereas (C, F, I, L) are dorsal views; (A and G) correspond to frontal views. Abbreviations: lp, lens placode; dt, dorsal telencephalon; tg, trigeminal ganglion; vt, ventral telencephalon; hab, habenular nucleus; tec, tectum; rn, rhombencephalic neurons. Except for the frontal views, embryos are oriented with the anterior to the left; in lateral views, dorsal is up.

Expression of er81 does not require FGF signalling. Wholemount in situ hybridisation detecting pea3 (A and B), erm (C and D), etv5 (E and F) and er81 (G and H) in embryos treated with the FGF inhibitor SU5402 (B, D, F, H) or in DMSO treated control embryos (A, C, E, G). Embryos treated with SU5402 show a strong decrease of erm, pea3 and etv5 expression whereas er81 expression is not affected. Embryos are shown from the dorsal aspect and oriented anterior to the left.