Fig. 1. Tsg is epistatic to Tld. Embryos were hybridized with antisense digoxigenin-labeled rhomboid probes. Mutant embryos were identified by lack of hybridization to lacZ transcripts produced from the FM7, ftz-lacZ and TM3, ftz-lacZ balancer chromosomes. Embryos are positioned with their dorsal side upwards and anterior towards the left. (A) Wild-type embryo, (B) tsg mutant embryo, (C) tld mutant embryo and (D) tsg, tld mutant embryo. The expression of rho on the dorsal side is broader and weaker in tsg mutants or tsg, tld double mutant embryos, than that in the wild type. In the tld mutant embryo, rho was expressed in its normal ventral domain, but not on the dorsal side, except for a thin anterior stripe.