Light-avoidance-mediating photoreceptors tile the Drosophila larval body wall

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Photoreceptors for visual perception, phototaxis or light avoidance are typically clustered in eyes or related structures such as the Bolwig organ of Drosophila larvae. Unexpectedly, we found that the class IV dendritic arborization neurons of Drosophila melanogaster larvae respond to ultraviolet, violet and blue light, and are major mediators of light avoidance, particularly at high intensities. These class IV dendritic arborization neurons, which are present in every body segment, have dendrites tiling the larval body wall nearly completely without redundancy. Dendritic illumination activates class IV dendritic arborization neurons. These novel photoreceptors use phototransduction machinery distinct from other photoreceptors in Drosophila and enable larvae to sense light exposure over their entire bodies and move out of danger.

At a glance


  1. Photoreceptors in addition to Bolwig organs contribute to photoavoidance.
    Figure 1: Photoreceptors in addition to Bolwig organs contribute to photoavoidance.

    a, b, Examples of light avoidance of wild-type (a) and GMR-Hid (b) larvae exposed to white light (0.57mWmm−2) applied from 0 to 5 s. The light spot is indicated by the dotted circle. The arrow indicates the direction of larval locomotion; arrowheads at 2s (a) and 5s (b) indicate larval head turning. ch, Percentage of animals avoiding white light (c), light of 360nm (ultraviolet; d), 402nm (violet; e), 470nm (blue; f), 525nm (green; g) and 620nm (red; h) at different intensities. *P<0.05, **P<0.01, ***P<0.001, two-tailed Fisher exact test. Twenty to forty larvae were tested for each condition. Scale bar: 1 mm (a, b), shown at −2s.

  2. Light activates class IV dendritic arborization neurons.
    Figure 2: Light activates class IV dendritic arborization neurons.

    a, Pre-stimulation image showing larval dorsal cluster sensory neurons (dbd, bipolar dendrite neuron; ddaD and ddaE, class I dendritic arborization neurons; ddaB, class II dendritic arborization neurons; ddaA and ddaF, class III dendritic arborization neurons; ddaC, class IV dendritic arborization neurons; ES, external sensory organ). Up is dorsal; right is anterior. For an atlas of the larval peripheral nervous system, see ref. 25. b, Responses of the dorsal cluster neurons in a to 5s blue light (470nm) illumination. The boxed area in the left panel and insets in all three panels show the somas of ddaC, ddaF and ddaD dendritic arborization neurons. Left, pre-stimulation; middle, post-stimulation; right, GCaMP3 intensity difference (middle panel minus left panel), with ddaC dendrites (arrow) and axon (arrowhead) marked. c, d, Similar experiments with 5s green (546 nm; c) and ultraviolet light (365nm; d) revealed ddaC activation by ultraviolet, but not green, light. Scale bar in ad, 20μm; colour scale in right panels of bd shows dynamic range (0–4,095). e, Time course of somatic GCaMP3 signals of dorsal cluster neurons shown in ad. Time frames are indicated. f, Summary of somatic fluorescence changes (ΔF/F) of dorsal cluster neurons in response to 5s light stimulation, n = 7–16. g, Example firing traces of ddaC in response to 5s 470nm blue light. h, Summary of firing frequency changes (average frequency of 5s before light exposure subtracted from average frequency during 5s of light exposure) of ddaC induced by white, 340, 380, 402, 470, 525 and 620nm light. For clarity, significance is only shown for the 340nm curve. Light intensity is reported as the log of (I normalized to I0 = 1mWmm−2). Green (525nm) or red (620nm) light has no effect (P>0.05). n = 5–9. i, Effect of 1.4mWmm−2 white light on ddaC, average frequencies of 5s before (control) and during the 5s of light exposure (light) are plotted. n = 6. *P<0.05, **P<0.01, ***P<0.001; two-tailed paired t-test. All error bars indicate s.e.m.

  3. Cell-autonomous activation of class IV dendritic arborization neurons by light.
    Figure 3: Cell-autonomous activation of class IV dendritic arborization neurons by light.

    a, b, Quantification of somatic fluorescence changes (ΔF/F) in response to 5s light and 100μM allyl isothiocyanate (AITC) stimulation of cultured class IV (a) and III (b) dendritic arborization neurons; RFP signals serve as control. n = 10–13 (light) and n = 4 (AITC) in a, n = 9 in b. c, Larva with class IV dendritic arborization neurons labelled with GFP by ppk-GAL4. Dendrites tile the body wall. Boxed area shows an abdominal hemi-segment; three dotted circles mark soma positions of D (dorsal, ddaC), L (lateral, V′ada) and V (ventral, VdaB) class IV dendritic arborization neurons, respectively. Up, dorsal; left, anterior. Scale bar, 200μm. d, Illumination of dendrites within the dotted circle of GFP-labelled ddaC dendrites. Up, dorsal. Scale bar, 50μm. e, Responses of ddaC with dendritic illumination. n = 5. *P<0.05, **P<0.01, ***P<0.001; two-tailed paired t-test. All error bars indicate s.e.m.

  4. Gr28b and TrpA1 are essential for class IV dendritic arborization neuron light responses.
    Figure 4: Gr28b and TrpA1 are essential for class IV dendritic arborization neuron light responses.

    a, No significant defects were detected between wild-type and mutants of known phototransduction molecules with 340, 380, 402, 470, or 620nm light. n = 5–10. b, Reduced light response of class IV dendritic arborization neurons in MiET1 and PBac larvae. n = 8–29. c, Reduced light response of class IV dendritic arborization neurons in MiET1/deficiency larvae. n = 5–12. d, Precise excision of MiET1 P-element insertion restores light response in class IV dendritic arborization neurons. n = 6–9. e, Reduced light responses of class IV dendritic arborization neurons with Gr28b RNAi knockdown. n = 5–8. f, Abolished light responses of class IV dendritic arborization neurons in TrpA1−/− mutants. n = 8–13. g, MARCM analysis of TrpA1+/− and TrpA1−/− class IV dendritic arborization neurons’ response to light. n = 5–8. For ag, Light intensities (mWmm−2) are: 1.15 (340nm), 5.79 (380nm), 11.4 (402nm), 52.8 (470nm), 43.4 (525nm), 29.6 (620nm) and 94.7 (white). For a, b, c, e, *P<0.05, **P<0.01, ***P<0.001; one-way ANOVA followed by a Bonferroni post test; for d, f, g, *P<0.05, **P<0.01, ***P<0.001; two-tailed unpaired t-test. All error bars indicate s.e.m.

  5. Class IV dendritic arborization neurons are the extra-ocular photoreceptors that contribute to light avoidance.
    Figure 5: Class IV dendritic arborization neurons are the extra-ocular photoreceptors that contribute to light avoidance.

    a, b, Examples of larvae with either class IV dendritic arborization neurons ablated (a) or both Bolwig organs and class IV dendritic arborization neurons ablated (b) that failed to respond to white light (0.57mWmm−2) applied from 0 to 5 s (dotted circle). Arrow indicates locomotion direction. Scale bar, 1mm (a, b), shown at −2s. cg, Percentage of animals avoiding white light of different intensities (in mWmm−2: c, 0.088; d, 0.24; e, 0.57; f, 1.0; g, 1.67). Wild-type larvae, Bolwig-organ-ablated larvae (GMR-Hid), larvae with class IV dendritic arborization neurons ablated (ppk-GAL4; UAS-Hid,rpr) and larvae with both ablated (UAS-Hid,rpr; GMR-Hid; ppk-GAL4) were examined. h, Percentage of Bolwig-organ-ablated animals avoiding 0.25mWmm−2 525 nm green light when class IV dendritic arborization neurons express ChR2 with or without dietary retinal. i, Percentage of animals avoiding white light at 1mWmm−2. For ci, controls are black bars. Twenty to forty animals were tested for each condition; *P<0.05, **P<0.01, ***P<0.001; two-tailed Fisher exact test. ChR2, channelrhodopsin-2; rpr, reaper; NS, not significant.


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Author information


  1. Howard Hughes Medical Institute, Departments of Physiology, Biochemistry, and Biophysics, University of California San Francisco, San Francisco, California 94158, USA

    • Yang Xiang,
    • Quan Yuan,
    • Lily Yeh Jan &
    • Yuh Nung Jan
  2. Center for Developmental Genetics, New York University, New York, New York 10003, USA

    • Nina Vogt
  3. Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147, USA

    • Loren L. Looger


Y.X. designed and carried out the experiments and analysed the data; Q.Y. characterized molecular information of Gr28b, rhodopsin and cryptochrome. L.L.L. created GCaMP3 and did the bioinformatic analyses of Gr28b; N.V. cleaned up the Rh31 and Rh41 mutants; Y.N.J. helped to design the experiments and supervised the work; Y.X., L.L.L., L.Y.J. and Y.N.J. wrote the manuscript.

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  1. Supplementary Figures (4.2M)

    The file contains Supplementary Figures 1-26 with legends.


  1. Supplementary Movie 1 (5.6M)

    This movie shows photoavoidance of a wt larva to the light spot of 0.57 mW/mm2.

  2. Supplementary Movie 2 (4.4M)

    This movie shows the photoavoidance of a Bolwig organ-ablated larva (GMR-Hid) to the light spot of 0.57 mW/mm2.

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