Genetic interaction suggests that dSTIM positively supports Notch signalling during the refinement of vein thickness. Wings expressing dSTIMRNAiin the posterior compartment induced by en.Gal4 (A, D). have thickened lateral veins IV and V. This phenotype is more severe in (D) than that of (A), since the en.Gal4 driver was introduced maternally (en(m)) in (D), while it was introduced paternally (en(p)) in (A). Wings from flies deficient in Notch expression (Df(1)N81k1) (B) have margin defects at the distal wing tip, moderate thickening of vein V, and deltas at the ends of veins (B). Expression of dSTIMRNAiinduced by en.Gal4 on a Notch deficiency background results in severe exaggeration of vein IV and V thickening (C) when compared to dSTIMRNAion a wild-type background (B), with no enhancement of margin defects. Note: in this instance (C), the en.Gal4 driver was introduced paternally, since Df(1)N81K1 hemizygous males are lethal. Expression of an activated Notch allele (TNΔBRV) induced by en.Gal4 (E) causes a reduction in the length of lateral vein V (arrowhead). Co-expression with dSTIMRNAi (F), results in a mutual suppression of phenotypes caused by the expression of each construct alone. Note: The wings presented in (E) and (F) should be compared to (D), since the en.Gal4 driver was introduced maternally.