Fig. 3. Expression patterns of At-Delta transcripts in Achaearanea. (A-C) A flat-mounted mid-stage 4 germ disc stained for At-Delta transcripts (A,B) and DNA (C). The boxed area in A is magnified in B and C. Arrowheads indicate At-Delta-expressing cells near, but not at, the rim of the forming germ disc. (D-F) A flat-mounted late stage 4 embryo stained for At-fkh (red), At-Delta (purple) transcripts and DNA (not shown). Both the germ disc (gd) and non-germ disc (non-gd) areas are presented. Nuclei of non-germ disc cells show a sparse distribution. All nuclei of non-germ disc cells in D were confirmed to associate with the signals of At-Delta (data not shown). The boxed area in D is magnified in E (surface) and F (inside). The At-Delta-expressing cells are distinct from cEND cells. (G,H) A flat-mounted mid-stage 5 germ disc stained for At-fkh (red) and At-Delta (purple) transcripts and DNA. The boxed area in G is magnified in H, which is merged with DNA staining (H, light blue). Paired and unpaired At-Delta-positive cells are evenly spaced. (I-K) Flat-mounted early (I), mid-(J) and late (K) stage 6 embryos stained for At-Delta (purple) and At-cad (red) transcripts. The area displaying interspersed At-Delta expression expands followed by fading from the center and appearance of At-cad expression. At-cad expression is detectable from mid-stage 6. (L,M) A flat-mounted early stage 6 germ disc stained for At-twi (purple) and At-Delta (red) transcripts. The boxed area in L is magnified in M. Arrows point at cells expressing At-twi and At-Delta. (N) Schematic illustrations showing changing expression patterns of At-Delta, At-fkh, At-twi and At-cad transcripts up to caudal lobe formation. (O-Q) Stage 7 (O), stage 8 (P) and stage 9 (Q) embryos stained for At-Delta transcripts. Anterior is to the top. Arrows in O and P indicate a band of At-Delta expression in the anterior region. This anterior expression is visible in K. Note that regularly aligned spotty signals are visible in the central nervous system. cl, caudal lobe; ex, extra-embryonic area; op, opisthosoma; pr, prosoma. Scale bars: 20 µm for A-N; 100 µm for O-Q.