Figure 3.

mid is required for the expression of multiple axon guidance molecules. (A1–B3) Stage 16 mid¹ mutant embryos and their heterozygous siblings were examined for frazzled mRNA expression. (A1–A3) A mid/+ heterozygous embryo shows clear expression of frazzled mRNA (A2) in mid-positive cells (A1). (B1–B3) mid¹ mutants show reduced or no expression of frazzled (B2) in mid mRNA-labeled cells (B1). (C1–D1) Stage 16 embryos stained with anti-Frazzled antibody. (C1) Normal CNS. (C2) mid¹ CNS is weakly stained than normal embryos. (C3) Restored Frazzled expression in an elav-Gal4/+; mid1/mid1; UAS-mid/+ embryo. (D1) Wild-type mechanosensory neurons. (D2) No signal was detected in the mid¹ mechnosensory neurons. (D3) Restored Frazzled expression in the mechnosensory neurons of an elav-Gal4/+; mid¹/mid¹; UAS-mid/+ embryo. (E1–F3) Stage 16 mid¹ mutant embryos and their heterozygous siblings were examined for robo mRNA expression. (E1–E3) A mid/+ heterozygous embryo shows clear expression of robo mRNA (E2) in mid-positive cells (E1). (F1–F3) mid¹ mutants shows reduced or no expression of robo mRNA (F2) in mid mRNA-labeled cells (F1). (G1–G3) Stage 16 embryos stained with anti-ROBO antibody. (G1) Normal CNS. (G2) mid¹ CNS is weakly stained than normal. (G3) Restored ROBO expression in an elav-Gal4/+; mid1/mid1. (H1–H3) In situ hybridization analysis of slit expression in a stage 16 embryo. (H1) In normal embryo, the highest level of slit mRNA occurs in the midline glia (arrow), whereas low levels of slit mRNA are present in cells located lateral to the midline (arrowhead). (H2) In mid¹ mutant, silt mRNA expression in lateral regions is weaker than normal. (H3) Colocalization of mid (green) and slit (magenta) mRNA in lateral cells (arrowhead).