Spinal Cord Cells from Pre-metamorphic Stages Differentiate into Neurons and Promote Axon Growth and Regeneration after Transplantation into the Injured Spinal Cord of Non-regenerative Xenopus laevis Froglets.

Emilio E Méndez-Olivos,Rosana Muñoz,Juan Larraín

doi:10.3389/fncel.2017.00398

Emilio E Méndez-Olivos, Rosana Muñoz + Show 1 more

Open Access

https://doi.org/10.3389/fncel.2017.00398

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Abstract

Mammals are unable to regenerate its spinal cord after a lesion, meanwhile, anuran amphibians are capable of spinal cord regeneration only as larvae, and during metamorphosis, this capability is lost. Sox2/3+ cells present in the spinal cord of regenerative larvae are required for spinal cord regeneration. Here we evaluate the effect of the transplantation of spinal cord cells from regenerative larvae into the resected spinal cord of non-regenerative stages (NR-stage). Donor cells were able to survive up to 60 days after transplantation in the injury zone. During the first 3-weeks, transplanted cells organize in neural tube-like structures formed by Sox2/3+ cells. This was not observed when donor cells come from non-regenerative froglets. Mature neurons expressing NeuN and Neurofilament-H were detected in the grafted tissue 4 weeks after transplantation concomitantly with the appearance of axons derived from the donor cells growing into the host spinal cord, suggesting that Sox2/3+ cells behave as neural stem progenitor cells. We also found that cells from regenerative animals provide a permissive environment that promotes growth and regeneration of axons coming from the host. These results suggest that Sox2/3 cells present in the spinal cord of regenerative stage (R-stage) larvae are most probably neural stem progenitor cells that are able to survive, proliferate, self-organize and differentiate into neurons in the environment of the non-regenerative host. In addition, we have established an experimental paradigm to study the biology of neural stem progenitor cells in spinal cord regeneration.

Highlights

Worldwide an estimate of 3 million people live with Spinal Cord Injury (SCI) and approximately 180,000 new cases happen every year with severe implications for their quality of life (Lee et al, 2014)
To evaluate the ability of spinal cord cells from animals at R- and NR-stages to survive and engraft in the environment of a non-regenerative injured spinal cord, we developed a transplantation procedure based on protocols previously used for spinal cord transplantations in rats (Lu et al, 2012) and limb regeneration experiments in X. laevis (Lin et al, 2013)
For heterochronic experiments, corresponding to transplantation experiments using donor and host animals from different stages, we used as donors animals at Nieuwkoop and Faber (NF) stage 50 (R-stage) from the transgenic line Xla.Tg(CAG:Venus)Ueno that ubiquitously express the Venus reporter gene under the control of the CAG promoter and wild type juvenile froglets at NF stage 66 (NR-stage) as host (Figure 1A)

Summary

Introduction

Worldwide an estimate of 3 million people live with Spinal Cord Injury (SCI) and approximately 180,000 new cases happen every year with severe implications for their quality of life (Lee et al, 2014). Neural stem and progenitor cells (NSPC) are present in encephalic niches and physiological neurogenesis has been described (Kriegstein and Alvarez-Buylla, 2009), there is no formation of new neurons in the spinal cord in response to injury (Meletis et al, 2008; Sabelström et al, 2013). In those cases were NSPC have been detected in the spinal cord, cells that enter proliferation after injury are only fated to differentiate into astrocytes and oligodendrocytes (Horner et al, 2000; Meletis et al, 2008). It has been reported that ependymal cells proliferate after injury and form astrocytes and oligodendrocytes that contribute to a glial scar that limits the secondary damage (Meletis et al, 2008; Sabelström et al, 2013), this evidence seems controversial (Ren et al, 2017)

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