Ultrastructural organization of the MOs in fly campaniform mechanoreceptors. (A) Cartoon schematic of a fly. The red and blue arrowheads indicate the haltere and the tarsus of a leg, respectively. (B) Representative SEM images of haltere receptors (yellow arrowhead, upper panel) and a leg receptor (yellow arrowhead, lower panel). Scale bars, 30 µm (upper); 2 µm (lower). The cartoons on the right showed the cellular organization of the sensory neurons. OS, outer segment; IS, inner segment. (C) Lateral view of the outer segment (upper panel) of a haltere receptor and the corresponding cartoon schematic (lower panel). Genotype: DCX-EMAP-gal4, uas-cd4-tdtom/+. The OS, MO, and TB are indicated. Scale bar, 5 µm. (D) Lateral view (ET slice image) of the outer segment in a wild-type haltere receptor. Inset, cross-view of the MO. Scale bars, 300 nm. Also see Video 1. (E) The reconstructed model of microtubules in the MO of a haltere receptor. Scale bar, 100 nm. d₁, the inter-microtubule distance within the same array. d₂, the inter-array distance. (F) Probability density distribution of d₁ and d₂ in haltere receptors. The number of microtubule pairs was indicated. (G) Lateral view of the outer segment (upper panel) of a leg receptor and the corresponding cartoon schematic (lower panel). Genotype: DCX-EMAP-gal4, uas-cd4-tdtom/+. The OS, MO, and TB are indicated. Scale bar, 5 µm. (H) Lateral view (ET slice image) of the outer segment in a wild-type leg receptor. Scale bar, 300 nm. Also see Video 2. (I) Reconstructed model of microtubules in the MO of a leg receptor. Scale bar, 100 nm. d, the distance between adjacent microtubules. (J) Probability density distribution of d in leg receptors. d, the distance between adjacent microtubules. The number of microtubule pairs is indicated.