Tetrapod limb and sarcopterygian fin regeneration share a core genetic programme.

Salamanders are the only living tetrapods capable of fully regenerating limbs. The discovery of salamander lineage-specific genes (LSGs) expressed during limb regeneration suggests that this capacity is a salamander novelty. Conversely, recent paleontological evidence supports a deeper evolutionary origin, before the occurrence of salamanders in the fossil record. Here we show that lungfishes, the sister group of tetrapods, regenerate their fins through morphological steps equivalent to those seen in salamanders. Lungfish de novo transcriptome assembly and differential gene expression analysis reveal notable parallels between lungfish and salamander appendage regeneration, including strong downregulation of muscle proteins and upregulation of oncogenes, developmental genes and lungfish LSGs. MARCKS-like protein (MLP), recently discovered as a regeneration-initiating molecule in salamander, is likewise upregulated during early stages of lungfish fin regeneration. Taken together, our results lend strong support for the hypothesis that tetrapods inherited a bona fide limb regeneration programme concomitant with the fin-to-limb transition

Figure S1. Expression pattern of Phospho anti-Histone H3 in the larval retina; Figure S2. Expression pattern of sense-control probes in the larval retina. from Eye development in the four-eyed fish <i>Anableps anableps</i>: cranial and retinal adaptations to simultaneous aerial and aquatic vision

A. anableps eye at Stage 3 (a,b), Stage 4 (c,d) and Stage 5 (e,f). Hematoxylin and eosin stained cryosections (a,c,e). Phospho anti-Histone H3 (S10) (green) and DAPI (blue) immunofluorescence staining (b,d,f) Panels on third column are high magnification images of the ventral and dorsal ciliary marginal zone (CMZ) of the retina. DR, dorsal retina; VR, ventral retina; L, lens; Ir, iris; DC, dorsal cornea; VC, ventral cornea; Do, dorsal; Ve, ventral; Di, distal; Pr, proximal. Cryosections 20 µm, scale bars 500 µm.; In situ hybridizations using sense probes of visual opsins in eye sections of larvae of A. anableps: rh1 (a,b), rh2-1 (c,d), rh2-2 (e,f), sws2b (g,h), and lws (i,j). Scale bars are 50 µm