Zebrafish ryk expression profile. (A) Semiquantitative RT-PCR showing temporal ryk expression. (B–E) Whole-mount in situ hybridization reveals ubiquitous ryk expression throughout maternal (B) and gastrula stages (C–E) with enrichment in somites (E, arrowhead) and the central nervous system. (F) At 30 hpf, ryk is expressed in the brain and tail (arrowheads) and notably the eyes (inset). (G and H) At 4 dpf, ryk is expressed in the lining of ventricular zones (G, arrowheads) and notochord (H, arrowhead). Stages and orientation: 1.25 hpf, animal pole view; 8.5 hpf, lateral view; 15 hpf, dorsal view with anterior to the left; 19 and 30 hpf, lateral view with anterior to the left; 4 dpf, dorsal view of brain and lateral view of the whole body, anterior to the left.