The fin-to-limb transition as the re-organization of a Turing pattern

A Turing mechanism implemented by BMP, SOX9 and WNT has been proposed to control mouse digit patterning. However, its generality and contribution to the morphological diversity of fins and limbs has not been explored. Here we provide evidence that the skeletal patterning of the catshark Scyliorhinus canicula pectoral fin is likely driven by a deeply conserved Bmp–Sox9–Wnt Turing network. In catshark fins, the distal nodular elements arise from a periodic spot pattern of Sox9 expression, in contrast to the stripe pattern in mouse digit patterning. However, our computer model shows that the Bmp–Sox9–Wnt network with altered spatial modulation can explain the Sox9 expression in catshark fins. Finally, experimental perturbation of Bmp or Wnt signalling in catshark embryos produces skeletal alterations which match in silico predictions. Together, our results suggest that the broad morphological diversity of the distal fin and limb elements arose from the spatial re-organization of a deeply conserved Turing mechanism.This work was supported by the Spanish Ministry of Economy and Competitiveness, through ‘Centro de Excelencia Severo Ochoa 2013–2017’, SEV-2012-0208, and the Plan Nacional grant BFU2010-16428 and BFU2015-68725-P (co-financed by FEDER funds of the European commissions) to K.O., L.M., M.M. and J.S., and by ICREA to J.S. and in part by the Global COE Program ‘Evolving Education and Research Center for Spatio-Temporal Biological Network’ from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) and the Program for Leading Graduate Schools ‘Education Academy of Computational Life Sciences’ from the MEXT to K.O. and M.T., the Grant-in-Aid for Scientific Research (B) 25291086 and the Inamori Foundation to M.T