Fig. 9.
Mosaic analysis of the Isl1-GFP line. Mosaic animals were made by isochronically transplanting cells of the Isl1-GFP line into the normal embryo at the sphere stage to obtain stochastic labeling of cranial motor and sensory neurons. All images except for C are taken from larvae at ∼75 hr.C is from a larva at ∼90 hr. All figures are composite pictures made from the stacked confocal images. A,Lateral (slightly ventral) view of a mosaic larva in which GFP is expressed in the facial sensory ganglion cells (fs). B, C, Ventral (B) and dorsal (C) views of the same larva shown in A. a-fs shows the centrally projecting afferent facial sensory axons, which terminate in the dorsoposterior part of the hindbrain (arrowhead). The asterisk indicates signals derived from GFP-expressing cells in the mesencephalic region (Fig. 7A, a; B, d; see also single and double asterisks in E). Peripherally extending axons from the facial sensory ganglion cells take internal (in) and external (ex) pathways. Axons of both internal and external pathways terminate near the mouth. The internal fibers (correspond to a in Fig.6C) take a deep route, and most of the parts of the fibers are not visible, partly because they run out of the focal plane, and partly because of the opaque nature of the eye (lateral view) and cartilages (ventral view). The external fibers initially take the same superficial pathway as the seventh motor nerve and then diverge (Fig.6C, b;D,E, 7E, arrows). D, Lateral view of a mosaic larva in which GFP is expressed in neurons in the facial sensory ganglion (fs), in the glossopharyngeal sensory ganglion (gs), and the vagus sensory ganglion (short arrows). a-fs shows the centrally projecting afferent facial sensory axons, which terminate in the dorsoposterior part of the hindbrain (arrowhead). Thelong thin arrow indicates the faintly fluorescent centrally projecting axons from the glossopharyngeal sensory neurons. Terminals of the centrally projecting axons from the facial, glossopharyngeal, and vagus ganglion cells are located near one another in the dorsoposterior part of the hindbrain. The terminal region is likely to correspond to the nucleus tractus solitarii in the adult fish. We have examined a number of mosaic embryos in which GFP was expressed in the facial sensory neurons (n > 15). In all cases, centrally projecting fibers took the same pathway (Figs.6A,E, 7A,a-fs; 6C, green), and peripherally projecting fibers eventually terminated around the mouth.E, Dorsal view of a mosaic embryo in which GFP is expressed in a number of cells other than the motor neurons in the brain. The double-headed arrow marks the midline. Thedouble asterisks and the single asteriskindicate the GFP-positive cells in the mesencephalic region (Fig.7A, a; B, d). Anteriorly projecting processes from these cells (probably from the cells marked by the double asterisk) correspond to the tracts marked by cin Figure 7B, whereas posteriorly projecting processes from these cells (probably from the cells marked by the single asterisk) correspond to the tracts marked by ein Figure 7B. The posteriorly projecting axons may terminate around the trigeminal motor nucleus and facial motor nucleus (arrows). Scale bar, 100 μm.