Pruning that selectively eliminates neuronal processes is crucial for the refinement of neural circuits during development. In Drosophila, the class IV dendritic arborization neuron (ddaC) undergoes pruning to remove its larval dendrites during metamorphosis. We identified Sox14 as a transcription factor that was necessary and sufficient to mediate dendrite severing during pruning in response to ecdysone signaling. We found that Sox14 mediated dendrite pruning by directly regulating the expression of the target gene mical. mical encodes a large cytosolic protein with multiple domains that are known to associate with cytoskeletal components. mical mutants had marked severing defects during dendrite pruning that were similar to those of sox14 mutants. Overexpression of Mical could significantly rescue pruning defects in sox14 mutants, suggesting that Mical is a major downstream target of Sox14 during pruning. Thus, our findings indicate that a previously unknown pathway composed of Sox14 and its cytoskeletal target Mical governs dendrite severing.
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We thank H. Aberle, R. Barrio, Y.N. Jan, W.A. Johnson, the Bloomington Stock Center, Developmental Studies Hybridoma Bank (University of Iowa) and Vienna Drosophila RNAi Center for generously providing antibodies and fly stocks. We thank members of the Yu and Wang laboratories for stimulating discussions and Z.L. Ong for technical assistance. We thank W. Chia, S. Cohen, P. Rorth, S. Roy, J. Varghese and G. Feng for helpful discussions and for reading the manuscript. This work was supported by Temasek Life Sciences Laboratory (F.Y.), Duke–National University of Singapore (MOE2008-T2-1-048 and NRF-RF2009-02 to H.W.), and grants from the US National Institutes of Health and the National Institute of Neurological Disorders and Stroke (RO1NS35165) and the Howard Hughes Medical Institute (A.L.K.). D.K. is supported by the Singapore Millennium Foundation.
Supplementary Figures 1–12 (PDF 4803 kb)
The dynamics of dendrite removal in a ddaC neuron. Confocal time-lapse movie of a wt ppk-GAL4>mCD8GFP labelled ddaC neuron between 4 and 13 h APF. Frames were recorded every 6 minutes. (MOV 4108 kb)
Dendritic pruning is blocked in sox14Δ13 homozygotes. Confocal time-lapse movie of a ppk-GAL4>mCD8GFP labelled ddaC derived from a sox14Δ13 mutant pupa between 6 and 10 h APF. No severing or blebbing occurs in sox14 mutants during this period. Frames were recorded every 5 minutes. (MOV 1780 kb)
Dendrites of ddaCs are persisting drastically longer in mical15256 homozygotes. Confocal time-lapse recording of a mical15256 homozygous pupa, in which ddaCs are labelled by ppk-EGFP. Frames are recorded from 11 to 17 h APF with 5 minutes intervals. (MOV 4365 kb)
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