Cellular composition and organization of the spinal cord central canal during metamorphosis of the frog Xenopus laevis

Abstract

Studying the cellular composition and morphological changes of cells lining the central canal during Xenopus laevis metamorphosis could contribute to understand postnatal development and spinal cord regeneration. Here we report the analysis of central canal cells at different stages during metamorphosis using immunofluorescence for protein markers expression, transmission and scanning electron microscopy and cell proliferation assays. The central canal was regionalized according to expression of glial markers, ultrastructure, and proliferation in dorsal, lateral, and ventral domains with differences between larvae and froglets. In regenerative larvae, all cell types were uniciliated, have a radial morphology, and elongated nuclei with lax chromatin, resembling radial glial cells. Important differences in cells of nonregenerative froglets were observed, although uniciliated cells were found, the most abundant cells had multicilia and revealed extensive changes in the maturation and differentiation state. The majority of dividing cells in larvae corresponded to uniciliated cells at dorsal and lateral domains in a cervical-lumbar gradient, correlating with undifferentiated features. Neurons contacting the lumen of the central canal were detected in both stages and revealed extensive changes in the maturation and differentiation state. However, in froglets a very low proportion of cells incorporate 5-ethynyl-2'-deoxyuridine (EdU), associated with the differentiated profile and with the increase of multiciliated cells. Our work showed progressive changes in the cell types lining the central canal of Xenopus laevis spinal cord which are correlated with the regenerative capacities.

Cellular Response to Spinal Cord Injury in Regenerative and Non-Regenerative Stages in Xenopus Laevis

“…2H,I), and have an abundant number of mitochondria in the apical surface ( Fig. 2I, J) which resemble the lateral ependymal cells described before [48]. Unlike the response at the R-stage, froglets at the NR-stage are characterized by the absence of proliferation and rosette-like structures.…”

“…The cellular organization of the spinal cord CC in Xenopus laevis changes between regenerative and nonregenerative stages [48]. To determine the cellular response to spinal cord injury between regenerative (Rstages, NF stage 50) and non-regenerative (NR-stages, NF stage 66) stages, we performed a detailed cellular analysis.…”

“…Spinal cords were micro-dissected and post-xed overnight in the same xative. Spinal cords were processes as described before [48]. Brie y, spinal cords at different days post injury were post-xed in 2% osmium for 2 hr, rinsed, dehydrated, and embedded in araldite (Durcupan; Fluka, Buchs, Switzerland).…”

“…This ability is lost during metamorphosis (NF stage 66), and post-metamorphic animals including froglets are unable to regenerate the SC therefore are denominated as non-regenerative stages (NR-stages) [41][42][43][44][45][46][47]. At R-stages, most cells lining the CC have a radial glial morphology, are uniciliated, and express Sox2 [48]. While in NR-Stages, most cells lining the CC are multiciliated with an advance maturation and differentiation state and only few cells are uniciliated [48].…”

Model systems for regeneration: Xenopus

“…4A) (Bernardini et al, 2010;Gaete et al, 2012;Muñoz et al, 2015;Yoshino and Tochinai, 2004). Note that, although we term these cells 'NPCs', they are sometimes described in the literature as radial glia (RG) or ependymal cells (Chernoff et al, 2018;Edwards-Faret et al, 2018;McKeown et al, 2013).…”