Fig. 1

Cranial and spinal motor neuron development is affected in you-too (yot) mutants. Panels A–I show dorsal views of the hindbrain, and panels J–L show lateral views of the trunk, with anterior to the left. Asterisks in A–E indicate the location of nV motor neurons in rhombomere 2. Panels A–C are composite confocal images of embryos and identify GFP-expressing cranial motor neurons in the fluorescein channel, and zn5 antibody-labeled commissural neurons and axons at rhombomere boundaries (arrows) in the rhodamine channel. (A–C) In a 48-h post-fertilization (hpf) wild-type embryo (A), the nIII and nIV somatic motor neurons are located in the midbrain, the trigeminal motor neurons (nV; asterisk) in r2 and r3, the facial motor neurons (nVII; white arrowhead) in r5, r6, and r7, and the vagal motor neurons (nX; black arrowhead) in the caudal hindbrain (chb). The nV neurons are reduced in number in yot^ty17 mutants (B), and almost absent in yot^ty119 mutants (C), and, similarly, the nX neurons (black arrowheads) exhibit progressively severe losses in yot^ty17 and yot^ty119 mutants. While nVII neurons (white arrowheads) are also reduced in number in both mutant alleles, the reduction is less severe than those for nV and nX neurons. (D–F) At 36 hpf, the islet antibody labels hindbrain motor neurons in characteristic locations (arrowheads, asterisk; see panel A for details) in wild-type embryos (D), and these neurons are found in progressively reduced numbers in yot^ty17 (E) and yot^ty119 (F) embryos. (G) In a 48-hpf wild-type embryo, the zn5 antibody labels axons and cell bodies of the nVI abducens motor neurons in rhombomeres 5 and 6 (arrowhead), and the commissural neurons at rhombomere boundaries (arrow). (H and I) In both yot mutants, the commissural neurons (arrows) develop normally, while the nVI neurons are reduced in number in yot^ty17 mutants (H), and absent in yot^ty119 mutants (I). (J–L) At 36 hpf, the islet antibody labels motor neurons in the ventral spinal cord (bracket) in wild-type embryos (J), and these neurons are found in progressively reduced numbers in yot^ty17 (K) and yot^ty119 (L) embryos. The strongly labeled cells in the dorsal spinal cord (arrows) are Rohon-Beard sensory neurons. oto, otocyst; nc, notochord.