Ventral neural tube expression of vangl2, but not the endoderm, is required for FBM neuron migration. (A,B) Dorsal views of 36 hpf Tg(isl1:GFP) hindbrains stained for FBM neurons (arrowheads, GFP antibody). In sox32 morphant embryos, which lack endoderm, FBM neurons largely migrate normally out of r4, as in wildtype embryos. (C) Quantification of the FBM neuron migration phenotype in sox32 morphant embryos. Number of embryos in parentheses. (D–H) Dorsal views of 36 hpf Tg(isl1:GFP) host hindbrains (D,F), with the level of r4 cross-sections (E,G,H) indicated by broken lines. In D and E, motor neurons and donor-derived cells are both labeled brown due to streptavidin-conjugated alkaline phosphatase reactivity used to detect anti-GFP antibody binding (motor neurons) and biotinylated rhodamine dextran (vangl2 MO donor cells). In F–H, the endogenous fluorescence from GFP and rhodamine were used to identify the motor neurons and donor-derived cells, respectively. Inadvertant targeting of vangl2 morphant cells to the ventral neural tube (white arrow, E) in a wildtype host (D) results in failure of host FBM neurons to migrate (black arrowhead in D,E) on one side, with normal migration on the other (white arrowheads). Conversely, inadvertant targeting of wildtype cells (rhodamine dextran tracer, red) to the ventral neural tube (white arrows, F–H), including the floor plate (not visible due to very weak fluorescence), in a vangl2 morphant host (F) rescues the migration defect of host FBM neurons (black arrowheads, F–H). fp, floor plate; oto, otic vesicle.
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