Background: Mammals are not able to restore lost appendages, while many amphibians are. One important question about epimorphic regeneration is related to the origin of the new tissues and whether they come from mature cells via dedifferentiation and/or from stem cells. Several studies in urodele amphibians (salamanders) indicate that, after limb or tail amputation, the multinucleated muscle fibres do dedifferentiate by fragmentation and proliferation, thereby contributing to the regenerate. In Xenopus laevis tadpoles, however, it was shown that muscle fibres do not contribute directly to the tail regenerate. We set out to study whether dedifferentiation was present during muscle regeneration of the tadpole limb and zebrafish larval tail, mainly by cell tracing and histological observations. Results: Cell tracing and histological observations indicate that zebrafish tail muscle do not dedifferentiate during regeneration. Technical limitations did not allow us to trace tadpole limb cells, nevertheless we observed no signs of dedifferentiation histologically. However, ultrastructural and gene expression analysis of regenerating muscle in tadpole tail revealed an unexpected dedifferentiation phenotype. Further histological studies showed that dedifferentiating tail fibres did not enter the cell cycle and in vivo cell tracing revealed no evidences of muscle fibre fragmentation. In addition, our results indicate that this incomplete dedifferentiation was initiated by the retraction of muscle fibres. Conclusions: Our results show that complete skeletal muscle dedifferentiation is less common than expected in lower vertebrates. In addition, the discovery of incomplete dedifferentiation in muscle fibres of the tadpole tail stresses the importance of coupling histological studies with in vivo cell tracing experiments to better understand the regenerative mechanisms.
Bibliographical noteFunding Information:
We thank Carme Fabregat, Lola Mulero, Cristina Pardo and Cristina Morera for technical assistance, Veronika Sander for critical revision of the manuscript and Chris Jopling for discussing ideas and sharing materials. The “MANDRA1 clone 7A10” monoclonal antibody developed by Glenn E. Morris was obtained from the Developmental Studies Hybridoma Bank developed under the auspices of the NICHD and maintained by The University of Iowa, Department of Biology, Iowa City, IA 52242. This work was partially supported by FCT grant reference number SFRH/BD/29865/2006 (AMCR). Work in the laboratory of JCIB was supported by MICINN, Fundacion Cellex, IPSEN Foundation, Sanofi-Aventis and the G. Harold and Leila Y. Mathers Charitable Foundation.
ASJC Scopus subject areas
- Developmental Biology