Fig. 4

Other sites of val expression in wild-type and val- embryos. All embryos are shown in dorsal view with anterior to the left except F,G which are lateral views. (A,B) At the 20 somite stage (19 h), val expression begins to be down-regulated, first in r5 and then in r6, and expression is first detected in a bilateral pair of cells in r4 (arrowheads). In val^b337 embryos (B) the r5/6 expression is absent but expression in these two cells occurs normally. (C) In this embryo, the right Mauthner cell was transplanted from r4 to r2 at the 12 somite stage (15 h), and val expression was detected at 19 h. The correlation of val expression with the transplanted cell (arrow) demonstrates that the bilateral pair of val-expressing cells in r4 are the Mauthner cells. (D,E) val expression in the lens in wild-type (D) and val^b337 embryos (E) at 19 h. (F,G) val expression in Rohon- Beard cells (arrowheads) and in the blood-forming region at the base of the hind-yolk (arrow) in wild-type (F) and val^b337 (G) embryos. (H,I) By 24 h, val expression is gone from r5 in both wild-type (H) and val^b337 (I) embryos but persists at low levels in r6 in wild-type embryos. Expression in r4 is no longer restricted to the Mauthner cell but now includes 10-15 cells in a lateral cluster (arrowhead). In val^b337 embryos at this stage (I) val expression is similarly upregulated in r4, but the cluster of val-expressing cells extends further caudally than in wild-type embryos (arrowhead). (J,K) val expression in the hindbrain of 42 h wild-type (J) and valb337 (K) embryos. Scale bars = 50 μm.