Tetrapod limb and sarcopterygian fin regeneration share a core genetic programme

Abstract

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.

Perspective: Appendage regeneration in amphibians and some reptiles derived from specific evolutionary histories

“…This capability was likely already present in sarcopterygian fish from which amphibians evolved, that also contain large genomes (see http://www.genome.size.com/results). Extant lungfishes possess some regenerative ability (Nogueira et al, ), and they have tadpoles similar to those of amphibians (Pough et al, ). Therefore it may be expected that also their ancestors likely possessed some regenerative abilities.…”

Noncanonical Hox, Etv4, and Gli3 gene activities give insight into unique limb patterning in salamanders

“…Only recently, new data from the fossil record emerged suggesting that preaxial polarity and salamander-like regenerative capacities likely evolved early in tetrapod evolution and independently from each other, with limb regeneration capacities preceding the first crown group-salamanders in the fossil record by at least 150 Ma (Fröbisch, Bickelmann, & Witzmann, 2014;Fröbisch et al, 2015). Furthermore, comparisons between the appendage regeneration program in axolotls and lungfish, the closest living relative of tetrapods, revealed striking similarities, lending further support for an ancient regeneration program (Nogueira et al, 2016). Research on limb regeneration has made great progress in the past decades, however most studies focused on the initiation of regeneration during blastemal phase and, for comparison purposes, its corresponding early developmental phases (Kumar et al, 2015;Roensch, Tazaki, Chara, and Tanaka, 2013;Tanaka, 2016;Torok, Gardiner, Shubin, & Bryant, 1998).…”

Tail regeneration in the Paleozoic tetrapod Microbrachis pelikani and comparison with extant salamanders and squamates

“…This highlights that the evolution and mode of tail autotomy (intra‐ vs. intervertebral) proceeded independently of the capacity to regenerate the tail and the degree of regeneration with or without the reestablishment of the caudal axial skeleton. Recent evidence on limb regeneration suggests, that the capacity to regenerate limbs, nowadays only present in salamanders among tetrapods, is an ancient feature of sarcopterygians (Fröbisch et al ., , ; Nogueira et al ., ). Salamander‐like tail regeneration in the microsaurian Microbrachis suggests that tail regeneration may similarly be an ancient character among tetrapods.…”

“…() that revealed a pattern of up‐ or downregulation of molecular markers in the adult fin of the South American lungfish Lepidosiren paradoxa compared to the regenerated blastema very similar to modern salamanders, including the prominent role of MARCKS like proteins in the regeneration process. Indeed, this supports the hypothesis that regenerative capacities in the fins and limbs may be plesiomorphic for sarcopterygians rather than being derived for salamanders among tetrapods (Nogueira et al ., ).…”

“…the replacement of a lost structure via a blastema in salamander limb and tail regeneration and in squamate tail regeneration was therefore the subject of intensive research efforts with the ultimate goal to 1 day apply the findings in human medicine and clinical treatments (Alvarado, 2000;Brockes & Kumar, 2008;Alibardi, 2010a;Brockes & Gates, 2014;Tanaka, 2016). Recently, the evolution of regenerative capacities in various animal clades has shifted into focus, drawing upon and integrating different sources of information, including the fossil record, phylogenetic systematics and shared molecular signatures in regenerative processes (Brockes, Kumar & Velloso, 2001;Alibardi, 2010a;Bely & Nyberg, 2010;Bely & Sikes, 2010;Fr€ obisch, Bickelmann & Witzmann, 2014;Fr€ obisch et al, 2015;Kumar et al, 2015;Nogueira et al, 2016;Zattara & Bely, 2016). Data from the fossil record has provided evidence for salamander-like limb and tail regeneration in two lineages of Paleozoic early tetrapods, Temnospondyli and Lepospondyli (Fig.…”