Macrophages are essential for appendage regeneration after amputation in regenerative species. The molecular mechanisms through which macrophages orchestrate blastema formation and regeneration are still unclear. Here, we use the genetically tractable and transparent zebrafish larvae to study the functions of polarized macrophage subsets during caudal fin regeneration. After caudal fin amputation, we show an early and transient accumulation of pro-inflammatory macrophages concomitant with the accumulation of non-inflammatory macrophages which, in contrast to pro-inflammatory macrophages, remain associated to the fin until the end of the regeneration. Chemical and genetic depletion of macrophages suggested that early recruited macrophages that express TNFα are critical for blastema formation. Combining parabiosis and morpholino knockdown strategies, we show that TNFα/TNFR1 signaling pathway is required for the fin regeneration. Our study reveals that TNFR1 has a necessary and direct role in blastema cell activation suggesting that macrophage subset balance provides the accurate TNFα signal to prime regeneration in zebrafish.
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Acknowledgements. This work was supported by Inserm and grants from ‘Région Languedoc-Roussillon, Chercheur d’Avenir’ no. DGA3/DESR 2012/Q209, from the French National Research Agency ‘Zebraflam’ no. ANR-10-MIDI-009 and from the European Community’s Seventh Framework Program (FP7-PEOPLE-2011-ITN) under the Marie-Curie Initial Training Network FishForPharma (Grant Agreement No. PITN-GA-2011-289209). We thank the MRI facility for their assistance, J-P. Levraud (Institut Pasteur, France) for trans-shipping Tg(mpeg:Gal4;UAS:NTR-mCherry) line, A. Kawakami (Tokyo Institute of Technology, Japan) for junbl probe, M. Bagnat for tg(rcn3:gal4/UAS:dsRed) line and E. Lelièvre (Université de Montpellier, Montpellier) for providing support and advice during parabiosis experiments.
© The Author(s) 2017.