Fig. 3.

Hh-regulated events in yot^ty119 mutants are resistant to ectopic Hh pathway activation. Anterior is to left in all panels. Panels A–D show dorsal views, and panels E–L show lateral views. A–D are composite confocal images of embryos, and identify GFP-expressing branchiomotor neurons (green), and 3A10 antibody-labeled Mauthner neurons and axons in rhombomere 4 (red). (A and E) In control wild-type embryos, nk2.2 is expressed ventrally at all axial levels at 21 hpf (E), and branchiomotor neurons are found at their characteristic locations at 36 hpf (A). (B and F) In dnPKA RNA-injected wild-type embryos, nk2.2 is expressed at high levels, and at ectopic locations (arrowheads) in all rhombomeres (F). Branchiomotor neurons are also greatly increased in number (arrowheads), and found at ectopic locations at all axial levels (B). (C and G) In control yot^ty119 mutants, nk2.2 expression is missing throughout the hindbrain, except within r4 (G), and, concomitantly, there is a severe loss of branchiomotor neurons at all axial levels, except nVII neurons, which originate in r4 (C). (D and H) In dnPKA RNA-injected yot^ty119 mutants, nk2.2 expression is increased within its normal ventral domain in r4, and slightly within the caudal hindbrain (H, arrowheads). There is a corresponding increase in the number of branchiomotor neurons originating in r4 and the caudal hindbrain (arrowheads), but there is no effect on motor neurons in other rhombomeres (D). (I–L) In a control 21 hpf wild-type embryo (I), net1a is expressed ventrally at all axial levels (arrowheads), with dorsal expansion at rhombomere boundaries. In a dnPKA RNA-injected wild-type embryo (J), net1a expression is expanded dorsally (arrowheads) at all axial levels. In a control yot^ty17 mutant (K), net1a expression is reduced in all rhombomeres except r4 (arrowheads; compare to I). In a dnPKA RNA-injected yot^ty17 mutant (L), net1a expression is expanded dorsally in all rhombomeres including r2 and r4 (arrowheads).