<i>Drosophila Syx1A</i> genetically interacts with to <i>robo2</i> and <i>fra</i>.

<p>(A-D) Stage 16 embryos stained with anti-FasII to mark all FasII-positive axons. A, wt embryo showing the three FasII-positive longitudinal connectives. B, <i>Syx1A</i> mutant embryo showing the three longitudinal connectives closer to the midline. C, <i>fra</i>^<i>3</i> mutant embryo showing an increased distance between fascicles. D, <i>robo2</i> mutant embryo showing midline crosses and fascicles closer to the midline. (E) Quantification of the relative distance between fascicles in control (n = 20), <i>Syx1A</i> (n = 20), <i>fra</i> (n = 37) and <i>robo2</i> (n = 20) VNCs. Significant differences are labelled by asterisks (***p≤0.001). (F-I) Stage 16 embryos stained with anti-FasII to mark all FasII-positive axons and to better observe axonal pathway defects. F, <i>robo2</i> mutant embryo showing midline crosses (arrows) and fascicle collapses. G-I, <i>robo2;Syx1A</i> double mutant embryos representative of the three phenotypes encountered; G: Weak, H: Intermediate and I: Strong. Asterisks show fascicle collapses in the VNC in all cases. Anterior is up. (J) Quantification of the total number of axon guidance defects encountered in <i>Syx1A</i> (n = 38), <i>robo2</i> (n = 39) and <i>robo2;Syx1A</i> (n = 31) mutant embryos. Significant differences are labelled by asterisks (***p≤0.001). (K-N) Stage 16 embryos stained with anti-FasII to mark all FasII-positive axons and to better observe axonal pathway defects. K, <i>fra</i>^<i>3</i> mutant embryo showing fascicle defasciculation and collapse phenotypes (arrows). L-N, <i>fra;Syx1A/+</i> mutant embryos representative of the phenotypes encountered. Arrows point at defasciculation and collapsed phenotypes. (O) Quantification of the total number of axon guidance defects encountered in <i>fra</i> (n = 37), <i>Syx1A</i> (n = 31), <i>fra/+;Syx1A</i> (n = 15), <i>fra;Syx1A/+</i> (n = 8) and <i>fra;Syx1A</i> (n = 8) mutant embryos. Significant differences are labelled by asterisks (*p≤0.05,***p≤0.001). (P) Quantification of the relative distance between medial fascicles in control (n = 20), <i>Syx1A</i> (n = 20), <i>robo2</i> (n = 20) and <i>robo2;Syx1A</i> (n = 17) VNCs. Only accounted the cases like panel G, where fascicles had not collapsed.