Figure 3. Modulation of Wnt signalling by Notch during the patterning of the larval cuticle.

(A) Wild type pattern of the larval cuticle at the end of embryogenesis. The cuticle exhibits reiterated thick sets of denticles that demarcate the anterior part of each segment and are very prominent in the abdominal region; the posterior part of each segment is devoid of denticles and this phenotype requires Wingless signalling. (B-E) Ventral cuticles of larvae expressing UAS Arm^s10 (B, D), or UAS Arm^s10 together with UAS TNotch (C, E), under the control of armGAL4 at different temperatures. The activity of GAL4 is temperature dependent and elicits more expression of the genes under GAL4 UAS control at the higher temperature; this can be seen in the penetrance of the phenotypes (F-H). (B-D) Cuticles representative of the phenotypes caused by expression of Arm^s10 (B) or Arm^s10 together with TNotch (C) at 25°C. At this temperature GAL4 is very active and Arm^s10 consistently elicits the naked cuticle fate (see also F). TNotch suppresses the effects of Arm^s10 and allows the development of denticles (arrow). The effect of TNotch is more pronounced at 22°C (D, E), when the effects of Arm^s10 are weaker. At 18°C most embryos expressing Arm^s10 develop some denticles, however they tend not to cross the midline (see arrow in D). At this temperature the effects of TNotch on Arm^s10 are manifested in the appearance of denticles across the midline (see arrow in E). (F-H) Quantitative analysis of the effects of TNotch on Arm^s10 at different temperatures (25°C, 22°C and 18°C). (F and G) At 25°C and 22°C the effects of Arm^s10 were assessed by the number of embryos with 3 or less segments with denticles regardless of whether they cross the midline or not. Notice that at both temperatures (25°C, 22°C) embryos that express TNotch have more segments with denticles. (F and H) At 18°C most embryos expressing Arm^s10 have segments with denticles due to the low expression of Arm^s10. In this case we evaluated the number of embryos with denticle belts i.e. embryos in which the denticles cross the midline. As in( G), we chose 3 as an arbitrary threshold for our quantification. In this instance we also counted the number of embryos with naked cuticle. TNotch can suppress the effects of Arm^s10.