Fig. 5. BM and VM neurons in Tbx20 mutants display axon guidance defects. (A-H) Axonal projections in flat-mounted hindbrains of SE1::gfp; Tbx20 mutants and controls. GFP marks BM/VM neurons in SE1::gfp transgenic mice (see Fig. S3 in the supplementary material). Axonal exit points of BM/VM neurons (white arrowheads) in hindbrains from Tbx20 mutants are normal. In Tbx20 mutants, the cell bodies of trigeminal neurons (green arrowheads in E-G) partially migrate dorsolaterally toward the exit point (white arrowheads), whereas those of facial neurons (red arrowhead in E-G) fail to migrate. These observations are summarized in D and H. (I-N) Whole-mount neurofilament staining of axonal projections in E11.5 Tbx20 mutants and controls. (I,L) Trigeminal axons project toward their correct peripheral targets in Tbx20 mutants. (J,M) High power view of the embryos shown in I and L revealing abnormal facial axon pathfinding (VII, red arrowhead). (K,N) High power view from I and L at a different focal plane revealing defasciculation and misrouting of vagal (X) axons (red arrowheads); the dashed line indicates the projectory of vagal axons. Scale bar: in G, 500 µm for A-C, E-G.