Fig. 6

Expression of ptSox21b-1. Flat-mounted embryos at different stages of development after RNA in situ hybridization. a) ptSox21b-1 expression is detected from mid-stage 7 in the nascent segment (black arrowhead) and in the SAZ (white arrow). b) At stage 8.1, expression in the SAZ appears to be dynamic (white arrow, c.f. Figure 6a), and broadens in forming segments (black arrowheads). c) At stage 8.2, white arrows at the anterior indicate expression in the presumptive ventral nerve cord, with expression in the posterior SAZ still prominent (black arrowhead). d) At stage 9 strong expression in the entire anterior part of the ventral nerve cord is indicated by white arrows, expression is lower at the most posterior but appears to remain dynamic in the SAZ (black arrowhead). e) At stage 10, expression is visible in the ventral nerve cord beneath the growing limb buds (black arrowheads) and becomes strong in the entire ventral nerve cord (white arrows). Ch: chelicerae, HL: head lobes, L1 – L4: prosomal segments 1 to 4, O1 – O4: opisthosomal segments 1 to 4, Pp: pedipalps; SAZ: segment addition zone. Ventral views are shown for all embryos with the anterior to the left. Scale bars: 150 μm