Expression of zebrafish ngn1 during early development. Initially, expression is confined to six major domains, including paired domains contributing to the trigeminal ganglia and the dorsal spinal cord as well as the midbrain-hindbrain boundary (MHB) and the ventral part of the spinal cord. Later in development this pattern resolves in finer detail, allowing the description of specific ngn1-positive cell lineages. Anterior is toward the left, except in A, where anterior is up. A: 8.5 hours postfertilization (hpf); dorsal view of a neural plate after the yolk has been removed. B: 12 hpf; dorsal view of the anterior neural plate; arrowhead, cells spanning the dorso-ventral axis of the neural plate. C: 12 hpf; dorsal view of the posterior neural plate; arrowhead, cells expressing ngn1 close to the caudal end of the notochord. D: 15 hpf; side view. F: 15 hpf; dorsal view; arrowheads indicate the position of a border-like group of cells; arrow, the anterior extent of the floor plate; asterisk in F, the anterior extent of the neural plate. Note the lack of ngn1 transcripts in the telencephalon. E: 20 hpf; side view, G: 20 hpf; side view in the tail region; H: 20 hpf; dorsal view in the head (the embryo is slightly tilted to the left). I: 24 hpf; large open arrowhead, rhombomere 1; large arrowhead, rhombomeres; small arrowheads define the left otic vesicle, a, acoustic ganglion; c, cerebellum; d, dorsal spinal cord; dc, diencephalon; d m, diencephalic-midbrain border; e, eye; f, the position of the anterior extent of the floor plate; in, interneurons, mb, midbrain; mn, motoneurons; rb, Rohon-Beard cells; v, ventral spinal cord; t, telencephalon; tg, tegmentum; tr, trigeminal ganglion. Scale bars = 100 μm in A–F,H; 10 μm in G.
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