Fig. 2. T-Sp8 expression in wild-type Tribolium embryos. Successively older stages are shown from A-F. (A) T-Sp8 is expressed in segmental stripes in the complete embryo prior to limb bud formation. Only the thoracic segments (T1-3) and abdominal segment 1 (A1) are shown. (B) T-Sp8 is uniformly expressed in the young limb bud (arrowhead indicates the pleuropodium, the appendage of abdominal segment 1). (C) T-Sp8 resolves into two rings but is still seen at the limb tip (arrowhead indicates the pleuropodia). (D) T-Sp8 begins to retract from the limb tip (arrowhead indicates the pleuropodia). (E) The process of leg elongation continues. No T-Sp8 expression is detectable in the pleuropodia (arrowhead). (F) A third, slightly weaker T-Sp8 domain (arrow) intercalates between the primary rings. (G) T-Sp8 expression in the head (same embryo as in D). Two ring-shaped expression domains can be seen in the antennae (arrowheads) and the outer branch of the maxillae, the telopodit (arrows). T-Sp8 expression is strong in the labial buds (Lb) and diffuse in the labrum (Lr). One small distal positioned T-Sp8 spot is visible in the mandibles (Md) that presumably marks a sensory organ. (H) T-Sp8 expression in the head (same embryo as in E). Strong T-Sp8 expression is seen at the distal tip of the antennae (arrowhead) whereas in the rest of this limb, T-Sp8 expression is diffuse. (I) T-Sp8 expression in the head (same embryo as in F). In the antennae, only the distal tip shows T-Sp8 expression (arrowhead). In the maxillae the proximal T-Sp8 domain is still visible (arrow). (J) The three rings of T-Sp8 expression are now fully developed (solid arrows) and a fourth ring appears (outlined arrow). The staining in the pleuropodia (arrowhead) is due to a known artefact. (K,L) Double labelling of T-Sp8 (in blue) and Distal-less (Dll, in red) expression reveals that the proximal T-Sp8 ring lays outside of the distal Dll expression domain (arrowhead indicates the pleuropodia in J).