Fig. 2

Hh signaling is significantly normal in rhombomere 4 of yot mutants. Panels A, B, E–H, and M–S show lateral views of hindbrain, with anterior to the left. Panels C and D show dorsal views with anterior to the left. Panels I–L show cross sections of the hindbrain (top is dorsal) at the indicated rhombomere levels. (A–D) In 21 hpf wild-type embryos (A and C), nk2.2 is expressed (arrowhead) in the ventral neural tube at all axial levels. In yot^ty119 mutants (B and D), nk2.2 expression (arrowhead) is virtually absent at all axial levels, except in rhombomere 4 (r4), delineated by the expression of krox20 in r3 and r5. Within r4 (D), the nk2.2 expression domain is slightly reduced compared to wild-type. (E–H) In 21 hpf wild-type embryos, ptc1 (E) and net1a (G) are expressed (arrowheads) at all axial levels in the ventral neural tube. In yot^ty119 mutants, ptc1 expression (F) is greatly reduced, with significant expression retained in r4 (arrowhead). Similarly, while net1a expression is substantially reduced in the yot^ty119 mutant hindbrain (H), it is significantly normal in r4 (arrowhead). (I–L) In rhombomere 4 (r4), ptc1 expression (arrowheads) in the ventral neural tube is comparable between wild-type (I) and yot mutants (J). In contrast, ptc1 expression in r6 (K) (arrowhead) is greatly reduced in yot mutants (L), while its expression in paraxial mesoderm (arrows) appears normal. Asterisk, notochord. (M–O) While nk2.2 is specifically expressed in r4 of mutants (N, arrowhead), nk2.2 expression in all rhombomeres, including r4 (arrowhead), is completely absent in wild-type and mutant embryos treated with cyclopamine (O). (P) In a control 30 hpf wild-type embryo treated with EtOH from 6 hpf, net1a expression is normal, with elevated expression in r4 (arrowhead). (Q) In a wild-type embryo treated with cyclopamine (CyA) from 6 hpf, net1a expression is completely absent at all axial levels. (R) In an embryo treated from 18 hpf, net1a is mostly expressed in r4 (arrowhead). (S) In an embryo treated from 24 hpf, net1a expression is mostly normal, with prominent expression in r4 (arrowhead). Asterisks in P–S mark the anterior end of the notochord in r4.