Fig. 6. RBs and DRG neurons are not necessarily derived from the same neural plate precursor cell. Embryos were injected with rhodamine-dextran into one cell at the 32-cell stage. Of 60 successfully labeled embryos, 10 had labeled RBs at 24 hpf, a frequency that is consistent with earlier experiments (Kimmel and Warga, 1987). We fixed all embryos at 48 hpf and processed them to reveal Hu-immunoreactivity. (A-F) Transverse sections near somite 10 of 2 dpf embryos. (A) Bright field image of an embryo with a labeled RB. The neural tube has been outlined to make it more obvious. (B) Lineage-tracer distribution in the section shown in A. Asterisk indicates a labeled RB, recognizable by its large cell body and dorsal position. (C) Anti-Hu immunoreactivity in the section shown in A. Although a DRG neuron (arrowhead) is present in this section, it does not contain lineage tracer, nor did any other DRG neurons in this embryo (not shown). (D) Bright field image of a different embryo that had a labeled RB at 24 hpf. This section was torn in processing. The neural tube has been outlined to make it more prominent. (E) Lineage-tracer distribution in the section shown in D. Arrowhead indicates a lineage-labeled DRG. (F) Anti-Hu immunoreactivity in lineage-labeled cell indicates that it is a neuron (arrowhead). Scale bar: 25 µm.