Fig. 1. The tor^GOF mutant phenotype is suppressed by loss of mrl activity. (A,C,E) tll mRNA expression patterns. (B,D,F) Larval cuticles. (A) In wild-type embryos, tll expression is restricted to the anterior and posterior poles. The posterior tll expression domain occupies 15% of egg length (EL). The anterior tll expression is controlled by both the Tor and Bicoid pathways (Pignoni et al., 1992) and is not discussed in this paper. (B) A wild-type larva has eight ventral abdominal denticle bands (A1 to A8), and posterior spiracles containing Filzkörper materials (arrowhead). (C) Embryos laid by females heterozygous for tor^Y9, a gain-of-function allele, show expansion of tll expression domains that causes enlargement of the terminal cell fates at the expense of the central cell fates (Klingler et al., 1988). As a consequence, (D) most denticle bands are frequently deleted, and occasionally ectopic Filzkörper material can be observed (arrowhead). (E) Removal of the maternal mrl gene product from tor^Y9 embryos resulted in a reduction of the ectopic tll expression associated with tor^Y9 to levels similar to those of wild-type embryos (see Materials and Methods). (F) The ventral denticle bands were mostly restored in these embryos and they exhibit phenotypes that are similar to mrl embryos derived from homozygous germline clones (GLC embryos). Similar results were obtained when a second gain-of-function tor mutation, tor^RL3, was used (data not shown).