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

Acacio F Nogueira,Chris T Amemiya,Mark Robinson,Sylvain Darnet,Carolina Furtado,Rodrigo N Moreira,Gabriela N Frota-Lima,Carinne M Costa,Jamily Lorena,Igor Schneider

doi:10.1038/ncomms13364

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.

Highlights

Salamanders are the only living tetrapods capable of fully regenerating limbs
Recent fossil evidence suggests an ancient origin of limb regeneration in tetrapods, as regeneration pathologies typically found among modern salamanders such as duplication or bifurcation of metacarpals, metatarsals and phalanges, as well as developmental asymmetry between the limbs within an individual, were reported in 300 million-year-old temnospondyl[1] and lepospondyl amphibians[2], B80 million years before the estimated origin of stem salamanders
Our results showed that genes encoding cell cycle components including Mcm[2], Pcna, Cdc[20], Plk[1] and Ccnb[1], focal adhesion genes such as Itga[8], Itgb[5] and Itga[11], as well key genes encoding extracellular matrix (ECM) components and modulators Mmp[8], Mmp[9], Mmp[13], Timp[1], Col5a1, Col12a1, Emilin[1] and Fn1, all typically overexpressed in salamander blastemas, were upregulated in the lungfish blastema

Summary

Introduction

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. 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. Limited taxonomic representation and scarce genetic resources have prevented in-depth comparisons of lungfish and salamander regeneration programs To address this question, we have examined fin regeneration in lungfishes, focusing on the morphological and molecular mechanisms leading to blastema formation. Our differential gene expression analysis reveals remarkable parallels between lungfish and salamander appendage regeneration, including strong downregulation of genes encoding muscle proteins, and upregulation of genes encoding matrix metalloproteinases, stem cell factors, and those involved in oncogenesis and developmental processes. The shared features of lungfish and amphibian appendage regeneration point to a common evolutionary origin, with new genes integrated into pre-existing regeneration programs

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Results

Conclusion