Fig. 4

spt5 is not required for facial branchiomotor neuron survival to at least 5 days postfertilization (dpf). Wild-type transplant hosts containing wild-type donor cells (red) and donor-derived motor neurons (yellow) at 5 dpf. A: Wild-type facial motor neurons (arrow) in a wild-type host migrate posteriorly, differentiate, and extend normal axonal processes from rhombomere 4 (r4). B: Hypomorphic foggy/spt5^fh20 facial motor neurons (arrow) placed in a wild-type host fail to migrate but are still detectable by green fluorescent protein (GFP) expression and have normal morphology with axons extending from r4 at 5 dpf; n = 12 of 13. C: The isl1-GFP motor neuron phenotype of the foggy/spt5^sk8 null allele at 48 hours postfertilization (hpf) demonstrates that facial motor neurons fail to migrate posteriorly from r4 (asterisk). D: foggy/spt5^sk8 null facial motor neurons (arrow) placed in a wild-type host fail to migrate normally but have axons extending from r4 at 5 dpf; n = 8 of 8. Scale bars = 40 μm in D (applies to A,B,D).