Figure S1.

Temporal dynamics and microglial engulfment of myelin abnormalities during CNS development in the mouse. (A−C) SBF-SEM of P10, P14, P21, and P60 wt mouse optic nerves (80 × 80 × 40–210 μm volumes with a 10 × 10 × 80 nm resolution). Quantifications include all time points for n = 1 optic nerve. (A) Mean number of myelinated axons within a 40 × 40 μm area (quantified on 8–10 evenly dispersed cross-sections within the SBF-SEM volumes). In total, we quantified 1,150 (P10), 3,559 (P14), 7,075 (P21), and 12,808 (P60) myelinated axons. (B) Mean percentage of myelin abnormalities (within 8–10 evenly dispersed volumes of 40 × 40 × 8 μm, normalized by the number of myelinated axons in reference sections). (C) Percentage of error subtypes among the myelin errors quantified in B: outfoldings (red), bulgings (yellow), degenerations (dark blue), fragments pinching off from a sheath or lying in the vicinity of a sheath (green), and minor outfoldings (light blue). (D) Quantification shows the number of microglia in a volume of 80 × 80 × 160 µm at P10, P14, P21, and P60 (n = 1). (E and F) SBF-SEM of a P14 wt mouse optic nerve shows two examples of a microglia engulfing degenerated myelin. Left: Pseudocolored cross-sections (blue: axon, magenta: myelin, green: microglia). Right: 3D reconstruction. Numbering refers to cross-sections. Scale bars: 2 µm.