Fig. 1

Fig. 1 Whole mount in situ transcript hybridisation analysis of the expression of spt and other genes in the tail and trunk of zebrafish embryos at approximately 22 hpf. In all images, dorsal is up and rostral is to the left. An apparently irregular rostrocaudal distribution of spt-expressing cells is seen in the developing CNS rostral to the domain of expression in the presomitic mesoderm of the extending tail (A). Boxed areas in A indicate parts of the image magnified in B and C. Shortly after their birth, these cells extend a process rostrally (indicated by a black asterisk in B) into which spt transcript is transported. spt is expressed in newly formed somites in a restricted region, the "somitic trail" (bracketed in C), at the same dorsoventral level as spt-expressing cells in the developing CNS (black arrowheads in any panel). The spt-expressing cells in the developing CNS (red stain) co-express huC, a marker of neurons (blue stain in D). A probe that identifies cells transcribing val (blue stain) shows that the spt-expressing neurons (red stain) are not identical with these (E). Transcription of the isl-1 gene (see F) is seen dorsally in Rohon-Beard neurons (black arrows in any panel), and ventrally in motoneurons (white arrow). Intermediate between these two levels are DoLA neurons that also express isl-1 (black arrowhead). Double staining with isl-1 (blue) and spt (red) shows that these intermediate-level neurons express spt (G). Costaining of spt (red) with isl-2 (blue in H) and isl-3 (blue in I) shows that the DoLA neurons also apparently express these genes, although the onset of expression occurs more rostrally than for isl-1. Scale bars equal 100 μm in A, B, C and F and 20 μm in D, E, G, H, I.