Fig. 2. Changes in the At-sog expression pattern. (A-F) At-sog expression is shown in embryos at mid-stage 5 (A) and stage 6 (B) viewed from the top of the germ disc, in an early stage 7 embryo viewed from the caudal (C) and lateral (D) sides, in a stage 7 embryo viewed from the lateral side (E), and in a stage 8 embryo viewed from the ventrolateral side (F). (A'-F') Schematic illustrations of the embryos shown in A-F. At-sog expression is shown in purple, yolk mass in yellow, the extra-embryonic area in orange, and the At-sog negative embryonic area in gray. Asterisks indicate the posterior of each embryo. Arrows in A and A' indicate the cumulus. Expansion of the extra-embryonic area and convergent extension of the embryonic area (D',E', arrows) transform the germ disc into the germ band. (G) A flat-mounted, stage 9 embryo stained for At-sog. (H,I) A transverse section of a stage 9 embryo stained for At-sog (H) and DNA (I). Arrowheads indicate limb buds, and brackets indicate the ventral midline area. (J) A flat-mounted, stage 5 germ disc stained for At-sog (purple) and pMad (brown). (J') High magnification of the region boxed in J. (K) Lateral view of a stage 7 embryo stained for pMad. The bracket indicates the extra-embryonic area, and the arrow indicates the boundary between the extra-embryonic and embryonic areas. (L) A flat-mounted, stage 8 embryo stained for At-sog (purple) and pMad (brown). (L') High magnification of the region boxed in L. (M,N) Flat-mounted, stage 9 embryos stained for At-sog (M, N, red) and At-fkh (M, purple) or At-sim (N, purple). (O,P) Stage 7 (O) and stage 8 (P) embryos stained for At-sog (red) and At-otd (purple). (Q,R,S,S') Expression of Pp-sog (Q,R) and Af-sog (S,S') transcripts. A ventral view of a Pholcus embryo at the germ band stage (Q). The tail part of a late-stage embryo (R). A ventral view of an Artemia nauplius (S). The region boxed in S is magnified in S'. a, anterior; p, posterior; d, dorsal; v, ventral; Ch, chelicerae; Pp, pedipalps; L1-L4, first to fourth walking legs. If not specified, anterior is to the top. Scale bars: 100 µm.