Fig. 5

Fig. 5

Temporal changes in competence to gbx2 at the MHB region. (A) Offspring embryos from a cross between wild-type and hsp70l:gbx2^+/– Tg fish were exposed to heat shock (HS) at the stages specified on the left and examined at 24 hpf for the expression of six3b, pax2a, and egr2b (left two columns) or shh and fgf8a (right two columns). The expression of six3b and egr2b in the forebrain and hindbrain (r3/r5), respectively, as well as the expression of shh in the hypothalamus, zli, and floor plate, and that of fgf8a in the forebrain were not affected, but pax2a and fgf8a expression at the MHB (solid triangles) was affected. Large open triangles represent complete disruption of MHB expression of pax2a or fgf8a and small triangles indicate incomplete downregulation. When isthmic expression was retained, expression gaps were observed intermediately along the DV axis. The proportions of the defects and total numbers of scored embryos are shown at the bottom in the respective panels. Approximately half of treated embryos were expected to harbor hsp70l:gbx2. (c–h, c′–h′) The numerators and denominators at the top-right show the numbers of hsp70l:gbx2^+/– embryos, determined by genotyping (B), and total embryos, respectively, showing that the MHB defects observed here were indeed due to gbx2 overexpression. Scale bar, 200 µm. (B) Genotyping of embryos exposed to HS at 80% epiboly. See the legend to Fig. 4D for details. pls, PCR product from hsp70l:gbx2 plasmid as a positive control. Embryos showing MHB mis-specification (MHB defect; downregulation of pax2a) alone possessed the transgene, showing that the defects observed at the MHB were due to gbx2 overexpression.