Abstract
Many animals possess mechanosensory neurons that fire when a limb nears the limit of its physical range, but the function of these proprioceptive limit detectors remains poorly understood. Here, we investigate a class of proprioceptors on the Drosophila leg called hair plates. Using calcium imaging in behaving flies, we find that a hair plate on the fly coxa (CxHP8) detects the limits of anterior leg movement. By reconstructing CxHP8 axons in an electron microscopy dataset, we found that they are wired to excite posterior leg movement and inhibit anterior leg movement. Consistent with this connectivity, optogenetic activation of CxHP8 neurons elicited posterior postural reflexes, while silencing altered the swing-to-stance transition during walking. Finally, we use comprehensive reconstruction of peripheral morphology and downstream connectivity to predict the function of other hair plates distributed across the fly leg. Our results suggest that each hair plate is specialized to control specific sensorimotor reflexes that are matched to the joint limit it detects. They also illustrate the feasibility of predicting sensorimotor reflexes from a connectome with identified proprioceptive inputs and motor outputs.
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Data availability
The calcium imaging, optogenetic, and treadmill kinematic silencing datasets generated in this study have been deposited in the Dryad database under https://doi.org/10.5061/dryad.fxpnvx153. All datasets are publicly available. FANC connectome data were analyzed from the CAVE materialization version 840, timestamp 2024-01-17T08:10:01.179472. FlyWire connectome data were analyzed from the public release version 783. Any additional information required to reanalyze the data is available from the lead contact upon request.
Code availability
Code for analyzing and visualizing hair plate connectivity in the EM dataset, calcium activity of CxHP8 neurons, kinematics during optogenetic experiments, and walking kinematics and posture during treadmill experiments is located on GitHub (https://github.com/Prattbuw/Hair_Plate_Paper/releases/tag/v1.0.0).
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Acknowledgements
We thank members of the Tuthill and Brunton Labs for technical assistance and feedback on the manuscript. We thank Seok Jun Moon for sharing the CxHP8 split-GAL4 driver line (R48A07 AD: R20C06 DBD). B.G.P. was supported by an NSF Graduate Research Fellowship (Fellow ID: 2018261272). C.J.D. was supported from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) project 432196121. Other support was provided by National Institutes of Health grants R01NS102333, R01NS128785, and U19NS104655, a Searle Scholar Award, a Klingenstein-Simons Fellowship, a Pew Biomedical Scholar Award, a McKnight Scholar Award, a Sloan Research Fellowship, the New York Stem Cell Foundation, and a UW Innovation Award to J.C.T. J.C.T. is a New York Stem Cell Foundation – Robertson Investigator.
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B.G.P. and J.C.T. conceived the study and wrote the manuscript. I.S. created the gorgeous Blender model of a fruit fly with hair plates, as well as Supplementary Video 2 B.G.P. and A.S. performed confocal imaging of hair plates. B.G.P. and A.C. proofread the hair plate axons and their downstream and upstream partners in FANC. C.J.D. collected and processed the calcium imaging data for CxHP8. G.M.C. and S.W.B. collected optogenetic activation and silencing datasets for CxHP8. B.G.P. analyzed the connectivity, calcium imaging, and optogenetic datasets. B.G.P. collected and analyzed the kinematics and posture of flies walking in the treadmill setup. A.A. provided valuable feedback about the connectivity of hair plates onto motor circuits.
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Pratt, B.G., Dallmann, C.J., Chou, G.M. et al. Proprioceptive limit detectors contribute to sensorimotor control of the Drosophila leg. Nat Commun (2026). https://doi.org/10.1038/s41467-026-69333-z
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DOI: https://doi.org/10.1038/s41467-026-69333-z
