Figure S5.
Structural defects in the haltere pedicellar campaniform mechanoreceptor and other ES mechanoreceptors in c01236/BE6. (A) Cartoon schematic showing the sensory neuron in the haltere pedicellar campaniform mechanoreceptors in c01236/BE6. All cellular segments were indicated. In comparison to wild type (Fig. 1), the major changes were: (1) the morphology of the outer segment was altered; (2) some vesicles appeared in the outer segment; and (3) microtubules in the outer segment were longer, but the total mass was reduced. (B–G) Cross-sectional views (ET slice images) of the MO (B), neck region (C), TB (D), cilium (E), mother centriole (MC; F) and daughter centriole (DC; G) in c01236/BE6. Note the appearance of microtubule doublets in the neck and in the central region of the TB (red arrowheads in C and D). (H) A representative ET slice image (x-z plane; thickness, ∼1 nm) from the stitched tomographic reconstruction showing that microtubules in the outer segment were long and extended into the MO (orange lines, microtubule traced in the volume data) in c01236/BE6. The visualization plane was adjusted to see microtubules. Scale bars in B–H, 250 nm. (I) Representative confocal images showing the MO (NompC-GFP labeling) of haltere scabellum receptors. Upper: nompC-gfp-KI. Lower: nompC-gfp-KI; c01236/BE6. Scale bar, 5 µm. (J) Statistical quantification of MO length in haltere scabellum receptors. (K) Representative confocal images showing the MO (NompC-GFP labeling) of the bristle receptors in wild type and c01236/BE6. Upper: nompC-gfp-KI. Lower: nompC-gfp-KI; c01236/BE6. Scale bar: 5 µm. (L) Statistical quantification of MO length in the bristle receptors in wild type (n = 6 labela, 30 cells) and c01236/BE6 (n = 6 labela, 18 cells). (M) Cartoon schematics showing the structural change in the MOs of wild-type and mutant bristle receptors. It is intriguing that the mutant MO becomes smaller in campaniform mechanoreceptors but gets longer in bristle receptors. We think that this is because the extracellular structures in these two types of mechanoreceptors are different. In campaniform receptors, the MO develops in a small space surrounded by other extracellular structures. In particular, a dome-like cuticular structure, called a cupola, overlies the distal end of the MO and prevents the MO from elongating further distally (Sun et al., 2019a). In the mutant, because microtubules are longer in length and fewer in number, the cytoskeleton in the MO cannot be well formed, which, in turn, resulted in a poorly developed (i.e., smaller) MO. In bristle cells, there is no cupola-like structure, and the lumen space of the bristle shaft potentially allows the MO (i.e., the NompC-positive region) to further elongate into the bristle lumen (Keil, 1997) when microtubules in the outer segment become much longer in the kat-60L1 mutants. In J and L, data are presented as mean ± SD with scattered data points. Two-sided unpaired Student’s t test was used for statistical analysis. ***, P < 0.001. The number of halteres or labela is indicated. Six cells were measured for each haltere and three cells for each labelum. BB, basal body.

Structural defects in the haltere pedicellar campaniform mechanoreceptor and other ES mechanoreceptors in c01236/BE6. (A) Cartoon schematic showing the sensory neuron in the haltere pedicellar campaniform mechanoreceptors in c01236/BE6. All cellular segments were indicated. In comparison to wild type (Fig. 1), the major changes were: (1) the morphology of the outer segment was altered; (2) some vesicles appeared in the outer segment; and (3) microtubules in the outer segment were longer, but the total mass was reduced. (B–G) Cross-sectional views (ET slice images) of the MO (B), neck region (C), TB (D), cilium (E), mother centriole (MC; F) and daughter centriole (DC; G) in c01236/BE6. Note the appearance of microtubule doublets in the neck and in the central region of the TB (red arrowheads in C and D). (H) A representative ET slice image (x-z plane; thickness, ∼1 nm) from the stitched tomographic reconstruction showing that microtubules in the outer segment were long and extended into the MO (orange lines, microtubule traced in the volume data) in c01236/BE6. The visualization plane was adjusted to see microtubules. Scale bars in B–H, 250 nm. (I) Representative confocal images showing the MO (NompC-GFP labeling) of haltere scabellum receptors. Upper: nompC-gfp-KI. Lower: nompC-gfp-KI; c01236/BE6. Scale bar, 5 µm. (J) Statistical quantification of MO length in haltere scabellum receptors. (K) Representative confocal images showing the MO (NompC-GFP labeling) of the bristle receptors in wild type and c01236/BE6. Upper: nompC-gfp-KI. Lower: nompC-gfp-KI; c01236/BE6. Scale bar: 5 µm. (L) Statistical quantification of MO length in the bristle receptors in wild type (n = 6 labela, 30 cells) and c01236/BE6 (n = 6 labela, 18 cells). (M) Cartoon schematics showing the structural change in the MOs of wild-type and mutant bristle receptors. It is intriguing that the mutant MO becomes smaller in campaniform mechanoreceptors but gets longer in bristle receptors. We think that this is because the extracellular structures in these two types of mechanoreceptors are different. In campaniform receptors, the MO develops in a small space surrounded by other extracellular structures. In particular, a dome-like cuticular structure, called a cupola, overlies the distal end of the MO and prevents the MO from elongating further distally (Sun et al., 2019a). In the mutant, because microtubules are longer in length and fewer in number, the cytoskeleton in the MO cannot be well formed, which, in turn, resulted in a poorly developed (i.e., smaller) MO. In bristle cells, there is no cupola-like structure, and the lumen space of the bristle shaft potentially allows the MO (i.e., the NompC-positive region) to further elongate into the bristle lumen (Keil, 1997) when microtubules in the outer segment become much longer in the kat-60L1 mutants. In J and L, data are presented as mean ± SD with scattered data points. Two-sided unpaired Student’s t test was used for statistical analysis. ***, P < 0.001. The number of halteres or labela is indicated. Six cells were measured for each haltere and three cells for each labelum. BB, basal body.

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