The Polarity Protein Scribble Regulates Myelination and Remyelination in the Central Nervous System
Fig 8
Conditional elimination of Scribble expression in oligodendrocytes disrupts paranodal axo-glial junctions and axonal domain organisation at the node of Ranvier.
A–F; In P40 Scribble cKO mice (C), paranodal axo-glial junctions in spinal cord or optic nerve (not shown) displayed an increased proportion of loops that had disengaged from the axonal surface (white arrows) relative to those in the CNS of wild-type littermates (A). This is quantified in B; WT ON: 0.8% ± 0.4%, cKO ON: 10.6% ± 1.8%, WT SC: 12.7% ± 2.4%, cKO SC: 24.1% ± 4.3%. Of the paranodal loops that faced the axolemma, a significantly increased proportion found in Scribble cKO mice were either linked to the axonal membrane by disordered electron density (F, arrow) instead of the ordered transverse bands seen in WT animals (E), or lacked transverse bands entirely (F, arrowhead). This is quantified in D; WT ON: 14.4% ± 1.7%, cKO ON: 53.4% ± 3.9%, WT SC: 19.9% ± 1.6%, cKO SC: 40.7% ± 3.5%. Results were presented as mean ± SEM. Student's t test was used. At least 20 nodes of Ranvier were analysed from each of three animals per genotype. G–I; Teased fibre preparations from P40 ventral spinal cord were used to assess myelin domain organisation at nodes of Ranvier in Scribble cKO mice and wild-type littermates. In Scribble cKO nerves, voltage-gated potassium channels normally localised to the juxtaparanode (Kv1.1, green) invade the paranode (J, arrowheads), encroaching on voltage-gated sodium channels at the node of Ranvier (Nav, red), while normal spacing is maintained in wild-type nerves (H), resulting in significantly reduced distances between sodium and potassium channel labelled regions (G; WT: 2.47 ± 0.09 μm, cKO: 1.13 ± 0.15 μm). This is due at least in part to widening of the Kv1.1-immunolabelled domain (I; WT: 18.0 ± 0.6 μm, cKO: 22.4 ± 1.3 μm). Results were presented as mean ± SEM. Student's t test was used. At least 30 nodes of Ranvier were analysed from each of four animals per genotype. * p < 0.05, ** p < 0.01, *** p < 0.001. Scale bars: A,C: 200 nm. E,F: 100 nm. H,J: 10 μm.