wg, Wnt2, Wnt4, Wnt7-1, Wnt7-2 and Wnt11-2 expression in Achaearanea. At-wg is expressed in the anterior ventral portion of the limb buds (a), but is not observed in ventral or dorsal regions of the prosomal segments or in the SAZ (b). Expression of At-wg extends along the axis of the growing legs and is observed in dorsal stripe in O2 and O3 (c) and later in O1 to O5 in groups of cells in the opisthosomal limb buds (d). At-Wnt2 expression is observed from stage 9 onwards in a central and lateral triangular shaped domain in the developing head lobes (e). At-Wnt4 is only expressed in a few cells at the very posterior of the SAZ during late embryonic development (f). Whereas At-Wnt7-1 is only expressed in the SAZ (g), At-Wnt7-2 is expressed at the base of the appendages and in a lateral anterior and posterior domain in the head lobes (h). At-Wnt11-2 expression appears at stage 6 in the posterior end of the embryo and persists in the SAZ throughout embryonic development (i). At-Wnt11-2 is also expressed in an anterior domain along the proximo-distal leg axis, the buds of the opisthosomal appendages and in the stomodeal region (i). Ch, cheliceres; Pp, pedipalps; L1 and L4, leg bearing segments; O1 to O5, opisthosomal segments; SAZ, segment addition zone. (a) to (d), ventral views of whole mounted embryos. (e), lateral view. (f), anterior view with posterior curving to the right. (g) to (i), flat mounted embryos with anterior to the left.