Abstract
Respiration in mammals relies on the rhythmic firing of neurons in the phrenic motor column (PMC), a motor neuron group that provides the sole source of diaphragm innervation. Despite their essential role in breathing, the specific determinants of PMC identity and patterns of connectivity are largely unknown. We show that two Hox genes, Hoxa5 and Hoxc5, control diverse aspects of PMC development including their clustering, intramuscular branching, and survival. In mice lacking Hox5 genes in motor neurons, axons extend to the diaphragm, but fail to arborize, leading to respiratory failure. Genetic rescue of cell death fails to restore columnar organization and branching patterns, indicating these defects are independent of neuronal loss. Unexpectedly, late Hox5 removal preserves columnar organization but depletes PMC number and branches, demonstrating a continuous requirement for Hox function in motor neurons. These findings indicate that Hox5 genes orchestrate PMC development through deployment of temporally distinct wiring programs.
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Acknowledgements
We thank C. Henderson, K. Kanning and I. Lieberam for discussions and sharing unpublished observations, M. Baek, H. Jung and C. Catela for comments on the manuscript, and P. Hallock and S. Burden for assistance with diaphragm preparations. L.J. is supported by a grant from the Canadian Institutes of Health Research (MOP-15139). J.S.D. is supported by grants from the McKnight Foundation, Alfred P. Sloan, Project ALS, NYSTEM, Howard Hughes Medical Institute and the US National Institutes of Health (R01 NS062822).
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P.P. performed all of the experiments except the Hoxc6−/− and Hb9∷Foxp1 analyses, which were performed by J.S.D. C.W. provided technical assistance with in situ experiments and serial sectioning, J.A. performed lung histology, L.J. provided the Hoxa5loxP/loxP mouse line, and P.P. and J.S.D. designed the study, analyzed the data and wrote the manuscript.
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Philippidou, P., Walsh, C., Aubin, J. et al. Sustained Hox5 gene activity is required for respiratory motor neuron development. Nat Neurosci 15, 1636–1644 (2012). https://doi.org/10.1038/nn.3242
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DOI: https://doi.org/10.1038/nn.3242
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