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Fig. 4 Foxi1-expressing progenitor cells are present at 24 hpf but fail to initiate ngn and phox2a expression in the no soul mutant. Anterior is to the left in A-L, and dorsal is to the top in M-N. (A-D) 24 hpf embryos showing that the foxi1-expressing domain is still intact in the no soul mutant and is apparently upregulated. (E-H) 24 hpf embryos showing that ngn and phox2a expression in the epibranchial placodes fail to be initiated in the no soul mutant. (I-L) Double in situ showing that while foxi1-expressing cells (red) are still present, they do not express ngn or phox2a (purple) in the no soul mutant. (M-P) Cross sectioning through the foxi1 (purple)- and phox2a (red)-expressing domain in 24 hpf embryos, showing that foxi1-expressing cells do not appear to delaminate and no phox2a+ sensory neurons are generated in the no soul mutant. (M,N) Nomarski views, (O,P) rhodamine fluorescence. The arrows point to the foxi1-expressing cells in the ectodermal layer, while the arrowhead points to cells that weakly express foxi1, are likely to be delaminating neural precursors, and overlapping phox2a+ epibranchial sensory neurons. AD, anterior dorsal lateral line; MHB, mid-hindbrain boundary; NP, neural plate; NT, neural tube; O, octaval/statoacoustic ganglion; ov, otic vesicle; OT, ocular and trochlear motor nuclei; VII, geniculate ganglion; IX, petrosal ganglion; X, nodose ganglion. Scale bar: 100 μm (A-B, E-H), 50 μm (C-D, I-L), 40 μm (M-P) 25 &mum.