Figure 6.

The majority of myelinating Schwann cells in the injured spinal cord are derived from PDGFRα+ progenitors. a, Twelve weeks after spinal cord contusion in PDGFRαCreER:YFP or mGFP mice, P0+ (red) Schwann cell myelin was abundant within the dorsal columns in areas of substantial astrocyte loss. There were two distinct populations (a″) of P0+ myelin sheaths, a YFP^NEG population (c′) and a YFP+ population (b, c″); most YFP^NEG P0+ myelin sheaths were found closer to the dorsal root entry zone, whereas the YFP+ P0+ sheaths were found mainly medially in the dorsal column (c″). b, Arrowheads point to YFP+/P0+ myelin sheaths with the cell bodies of a Schwann cells in the image plane. The arrow denotes an oligodendrocyte ensheathed YFP+ nerve fiber. The arrowheads denote fibers with a clear one-to-one sheath-to-cell ratio typical for Schwann cells (d, arrowheads). e, Schwann cell myelination was also apparent using the membrane-tethered reporter mGFP and horizontal sections through the lesion site (e, e′; dorsal to the left). f, The number of YFP+ myelinating Schwann cell profiles (green portion of bar) increased between 3 and 12 weeks after SCI (U₍₁₂₎ = 0.00, p = 0.001). There were significantly more overall myelinating Schwann cell profiles (gray + green portion of bar) at 12 wpi compared with 3 wpi (U₍₁₂₎ = 8.00, p = 0.035) and the majority of P0+ tubes were also YFP+. Images were taken in both epicenter spinal cord cross sections (a–d) and longitudinal sections near epicenter (e). *p < 0.05. Scale bars: a, e, 200 μm; c′, c″, a′, a″, 20 μm; e′, 10 μm; b, d, 5 μm. Error bars represent the SEM.