Fig. 2. Developmental regulation of receptor dimerisation. Dimerisation in embryos simultaneously expressing UAS-dome and UAS-dome, driven by either da-Gal4 (A-F), 69B-Gal4 (G-J), h-Gal4 (K-L) or 24B-Gal4 (M-N). Left panels show expression of the hybrid protein detected using an anti-ß-gal antibody, right panels show the X-gal patterns induced in those embryos by hybrid protein dimerisation. da-Gal4 and 69B-Gal4 embryos express ß-gal proteins in all ectodermal derivatives but they show X-gal staining in a subset of those cells (Right panels). h-Gal4 drives expression in stripes (K) but only the tracheal pits in each stripe show X-gal staining (L). Arrows in K-L point to tracheal pits where the hybrid proteins are expressed, and white arrowheads to a tracheal pits without expression. The 24B-Gal4 line drives high levels of expression in the mesoderm (M) but no X-gal expression is observed in this tissue (N). (A-B,K-N) Stage 11 embryos, (C-J) stage 13-14 embryos. When comparing embryos at the same developmental stage, all ectoderm Gal4 lines induce comparable X-gal staining (compare B with L, D with H and F with J). as, amnioserosa membrane; hg, hindgut; ms, mesoderm; ps, posterior spiracle; sg, salivary glands; tp, tracheal pits.