Fig. 5. Tollo mRNA is dynamically expressed throughout embryogenesis. The distribution of tollo mRNA was visualized by in situ hybridization with digoxigenin-labeled probes in OreR (A-F), TM3/TM3 (G) and Brd¹⁵/Brd¹⁵ (H) embryos. Message is first detected in distinct anterior and posterior bands at the cellular blastoderm stage (A) but rapidly spreads to include bands along the entire length of the embryo (B). At stage 12 (C,D), the extended germ-band demonstrates segmental expression. By stage 13 (E) ectodermal expression is restricted to domains within each segment. At higher magnification (F), stage 13 expression of tollo mRNA is not uniform within lateral ectodermal domains. TM3 homozygotes (G, stage 13) exhibit weak hybridization signal, while Brd¹⁵ homozygotes (H, stage 14) completely lack message. Scale bar: 450 µm in A-C,E,G,H; 125 µm in D,F.