pax-6 is expressed in zebrafish during neurulation. Whole embryos were hybridized with probes A and C, which are specific for pax-6. Hybridization with each probe alone gave identical results. (A, B) Dorsal view of the prospective brain region at 10 h. Two expression domains are discernible. The domain in the prospective forebrain appears earlier (A) than the one in the prospective hindbrain (B). The embryos differ slightly in age and show the gradual appearance of the hindbrain expression domain. Younger embryos show only the forebrain stripe (not shown). (C) Dorsal and (D) lateral view of a 10 h embryo, showing the two expression domains (h, hindbrain; f, forebrain). No expression is seen at the midline of the hindbrain (A, C and data not shown). (E, F) Lateral views of 14 h embryos. Expression is seen in the prospective forebrain (f), hindbrain (h) and the optic vesicle (ov). Anterior is to the left in A - C and up and to the left in D - F. Scale bar is 150 μm in A, B, C and 125 μm in D, E, F.