Genome-wide expression profile of the response to spinal cord injury in Xenopus laevis reveals extensive differences between regenerative and non-regenerative stages

Abstract

BackgroundXenopus laevis has regenerative and non-regenerative stages. As a tadpole, it is fully capable of functional recovery after a spinal cord injury, while its juvenile form (froglet) loses this capability during metamorphosis. We envision that comparative studies between regenerative and non-regenerative stages in Xenopus could aid in understanding why spinal cord regeneration fails in human beings.ResultsTo identify the mechanisms that allow the tadpole to regenerate and inhibit regeneration in the froglet, we obtained a transcriptome-wide profile of the response to spinal cord injury in Xenopus regenerative and non-regenerative stages. We found extensive transcriptome changes in regenerative tadpoles at 1 day after injury, while this was only observed by 6 days after injury in non-regenerative froglets. In addition, when comparing both stages, we found that they deployed a very different repertoire of transcripts, with more than 80% of them regulated in only one stage, including previously unannotated transcripts. This was supported by gene ontology enrichment analysis and validated by RT-qPCR, which showed that transcripts involved in metabolism, response to stress, cell cycle, development, immune response and inflammation, neurogenesis, and axonal regeneration were regulated differentially between regenerative and non-regenerative stages.ConclusionsWe identified differences in the timing of the transcriptional response and in the inventory of regulated transcripts and biological processes activated in response to spinal cord injury when comparing regenerative and non-regenerative stages. These genes and biological processes provide an entry point to understand why regeneration fails in mammals. Furthermore, our results introduce Xenopus laevis as a genetic model organism to study spinal cord regeneration.

Regeneration of Xenopus laevis spinal cord requires Sox2/3 expressing cells

“…All animal procedures were approved by the Committee on Bioethics and Biosafety from the Faculty of Biological Sciences, Pontificia Universidad Católica de Chile. For spinal cord transection, tadpoles and froglets were operated as described (Gaete et al, 2012; Lee-Liu et al, 2014). …”

“…In froglets we isolated the segment from the hindbrain, including the gap area, to the end of the spinal cord (approximate of 3 mm long). For RT-qPCR we isolated a fragment from the midpoint of the transection site (Lee-Liu et al., 2014). …”

“…We recently performed a transcriptome-wide profile analysis comparing the response to injury between regenerative and non-regenerative stages, and demonstrated that at each stage a very different gene repertoire is deployed in response to injury (Lee-Liu et al, 2014). Among other gene ontology groups we have found that neurogenic genes respond differentially between these two stages suggesting that activation of neural stem and progenitor cells and their differentiation into neurons could play an important role in spinal cord regeneration.…”

Neuronal Regeneration from Ependymo-Radial Glial Cells: Cook, Little Pot, Cook!

“…The gradual cessation of regenerative capacity at the onset of metamorphosis is studied mostly in the African clawed toad (Xenopus laevis) (Bernardini et al, 2010;Lee-Liu et al, 2014;Yoshino and Tochinai, 2004). Interestingly, there is also a non-regenerative period during larval development of the Xenopus tadpole, before and after which tail regeneration, including spinal cord, occurs (Beck et al, 2003).…”

Studying the expression patterns of OCT4 and SOX2 proteins in regenerating rabbit ear tissue

“…Various publications suggest that blastema contains dedifferentiated (Bellairs and Bryant, 1985;Carlson, 2011) or likely undifferentiated cells (Butler, 1935;Gurley and Alvarado, 2008;Tweedell, 2010), whereas different appendage regeneration studies showed that blastema tissues consisted of a heterogeneous population of different lineage restricted stem/progenitor cells (Kragl et al, 2009;Rinkevich et al, 2011;Lee-Liu et al, 2014). The later cell types have various origins and are not capable of differentiating into cells originated from other germ layers (Kragl et al, 2009;Rinkevich et al, 2011).…”