Fig. 5.

Effect of Pt-Sox21b-1 pRNAi knockdown on Pt-Msx1 expression. Pt-Msx1 is first expressed at stage 5 (A) in the presumptive region of the L2–L4 segments (dashed lines), forming a band of expression at stage 6 (B). At early stage 7 (C), two additional domains of expression arise in the SAZ and in a faint stripe corresponding to the presumptive head segments. This anterior stripe of expression becomes broader and more distinct by late stage 7 (D, black arrowhead) and the L2–L4 domain starts splitting into three stripes corresponding to each leg segment (black arrows). Faint expression is still present in the SAZ and a faint stripe can be detected in the first opisthosomal segment. Expression of Pt-Msx1 in stage 5 Pt-Sox21b-1 pRNAi embryos (E) is seemingly unaffected. At early stage 7 (F and G), Pt-Sox21b-1 knockdown does not affect the band of expression in the L2–L4 presumptive region (dashed lines). However, this domain does not split into stripes in late stage 7 (H; dashed lines). The anterior stripe of expression is unaffected in stage 7 knockdown embryos (F–H, black arrowhead), although Pt-Msx1 expression in the SAZ is lost. Anterior is to the left in all images except A and B. All embryos are flat mounted.