Fig. 2

Wild-type expression of ptc and hh genes during early development. Comparison of ptc and hh gene expression during the first 18 h of wild-type zebrafish embryogenesis. Transcripts were revealed by in situ hybridisation with antisense RNA probes to ptc1 (B, F, I, and K); ptc2 (A, E, G, H, and J); shh (C and L), and pax-b + ptc2 (D). (A–C) Dorsal views of embryos at the end of gastrulation (tail-bud stage) with their anteroposterior axis oriented vertically. ptc1 and ptc2 have different expression patterns at this stage; ptc2 is exclusively expressed in the neurectoderm above the midline (A), whereas ptc1 is also expressed in the adaxial cells and the presomitic mesoderm (B). (D–I) Dorsal flat preparations (with the yolk removed). Anterior is to the left. (D) ptc2 and pax-b expression at about 8 somites. pax-b is expressed in the midbrain–hindbrain boundary (shown with an asterisk) and the presumptive otic vesicle which is centred on presumptive rhombomere 5 but extends into presumptive rhombomeres 4 and 6 (indicated with a black square bracket). A stripe of ptc2 expression is visible in presumptive rhombomere 3 and a much weaker stripe of expression is present in rhombomere 5 (indicated with yellow double arrowhead lines); (E and F) ptc2 and ptc1 expression, respectively, at 5–6 somites and (L) a close-up of ptc2 expression in the caudal trunk at this stage. ptc2 is expressed throughout the medial lateral extent of the somites at this stage but ptc1 expression is still confined to the adaxial cells; ptc2 expression in the somites remains broader than ptc1 expression at 10–12 somites and this is shown in close-up (H and I). (J–L) Lateral views of embryos at 18 somites. ptc2 expression (J) is now clearly broader than ptc1 expression (K) in the brain, neural tube, and somites.