Neural stem/progenitor cells are activated during tail regeneration in the leopard gecko (Eublepharis macularius)

Abstract

As for many lizards, the leopard gecko (Eublepharis macularius) can self-detach its tail to avoid predation and then regenerate a replacement. The replacement tail includes a regenerated spinal cord with a simple morphology: an ependymal layer surrounded by nerve tracts. We hypothesized that cells within the ependymal layer of the original spinal cord include populations of neural stem/progenitor cells (NSPCs) that contribute to the regenerated spinal cord. Prior to tail loss, we performed a bromodeoxyuridine pulse-chase experiment and found that a subset of ependymal layer cells (ELCs) were label-retaining after a 140-day chase period. Next, we conducted a detailed spatiotemporal characterization of these cells before, during, and after tail regeneration. Our findings show that SOX2, a hallmark protein of NSPCs, is constitutively expressed by virtually all ELCs before, during, and after regeneration. We also found that during regeneration, ELCs express an expanded panel of NSPC and lineage-restricted progenitor cell markers, including MSI-1, SOX9, and TUJ1. Using electron microscopy, we determined that multiciliated, uniciliated, and biciliated cells are present, although the latter was only observed in regenerated spinal cords. Our results demonstrate that cells within the ependymal layer of the original, regenerating and fully regenerate spinal cord represent a heterogeneous population. These include radial glia comparable to Type E and Type B cells, and a neuronal-like population of cerebrospinal fluid-contacting cells. We propose that spinal cord regeneration in geckos represents a truncation of the restorative trajectory observed in some urodeles and teleosts, resulting in the formation of a structurally distinct replacement.

Immunodetection of High Mobility Group Proteins in the regenerating tail of lizard mainly indicates activation for cell proliferation

“…Previous ultrastructural and autoradiographic studies (Alibardi, 1990‐91, ) and more recent immunohistochemical studies (Gilbert & Vickaryous, ; Zhou et al., ) have indicated that progenitor/stem cells give rise to most glial and few neural cells during tail regeneration. While HMGb1 appears to stimulate regeneration and contrast inflammation after wounding (Dong et al., ), HMGa2 detected in ependymal cells instead likely indicates the presence of progenitor‐stem cells in these cells (Gilbert & Vickaryous, ; Zhou et al., ).…”

“…The immunofluorescent study has shown that the main localization of a HMGa2‐like protein occurs in tissues that drive tail regeneration, namely the apical wound epithelium and the regenerating spinal cord, mainly composed by an ependymal epithelium (Alibardi & Sala, ; Alibardi, Sala, & Miolo, ; Alibardi, 1990‐91, ; Alibardi, ; Cox, ; Gilbert & Vickaryous, ; Simpson, ; Zhou et al., ). These tissues show an active proliferation that is maintained in the apical regions of the regenerating tail while in proximal regions of the blastema, 1–2 mm from its tip, proliferation becomes less frequent and cells begin to differentiate into numerous tissue types.…”

“…Previous ultrastructural and autoradiographic studies (Alibardi, 1990(Alibardi, -91, 1993) and more recent immunohistochemical studies (Gilbert & Vickaryous, 2017;Zhou et al, 2013) have indicated that progenitor/stem cells give rise to most glial and few neural cells during tail regeneration.…”

“…A previous study on the amputated tail spinal cord of a gecko lizard (Gecko japonicus), indicated that HMGb-1b of 34 and 25 kDa, also with a high identity with the human protein, increases in the injured spinal cord, and it is present in the ependyma, neurons, microglia and also in macrophages (Dong et al, 2013). In particular the expression of HMG1b increased at 2 weeks after amputation, a period in which the ependymal canal has formed an apical ampulla and is growing inside the regenerative blastema (Alibardi & Sala, 1989;Gilbert & Vickaryous, 2017;Gilbert et al, 2015). The regenerating ependyma also allows the distal growth of some descending neurites, mainly derived from interneurons of the spinal cord proximal to the regenerating tail (Alibardi, 1990-91;Egar, Simpson, & Singer, 1970;Simpson & Duffy, 1994), and HMGs are known to stimulate axonogenesis and axonal growth (Dong et al, 2013;Nishino et al, 2008).…”

“…ALIBARDI While HMGb1 appears to stimulate regeneration and contrast inflammation after wounding (Dong et al, 2013), HMGa2 detected in ependymal cells instead likely indicates the presence of progenitor-stem cells in these cells (Gilbert & Vickaryous, 2017;Zhou et al, 2013).…”