Figure 6: Overexpression of gpr56 causes increased OPC number and inhibits myelination.

(a–d) WISH shows nkx2.2a expression in the spinal cord of injected WT larvae at 2.5 dpf. Lateral views are shown, dorsal is up. (e,f) Quantification of the number of nkx2.2a+ pro-OLs (black arrowheads) in WT embryos injected with 50 pg of synthetic gpr56 mRNA (N=30) in the anterior (b, segments 5–6, P<8.7 × 10⁻⁷) and posterior (d, segments 15–30, P<0.01) spinal cord compared with injected controls (a,c, N=31). (g–j) Representative images of a (h,j) gpr56-injected WT larva (N=19/31) compared with a (g,i) control-injected embryo (N=33/35) showing mbp expression by WISH. (g,h) Lateral views shown, anterior on right. (i,j) Dorsal views shown, anterior on right. Black arrows. (k) Cartoon of zebrafish larva in cross-section modified from Fig. 3b. White box represents regions shown in l,m,o,p. Green box represents region shown in r–u. (l,m,o,p) Representative images of spinal cord cross-sections from 2.5 dpf (l,m) and 5 dpf (o,p) WT embryos injected with control (l,o) or 50 pg gpr56 synthetic mRNA (m,p). 2.5 dpf: scale bar, 500 nm. 5 dpf: scale bar, 4 μm. (n,q) Quantification of the number of oligodendrocyte lineage cell bodies (shaded purple) in gpr56-injected embryos (N=4) compared with controls (N=4) at 2.5 dpf (P<0.037) and 5 dpf (P<0.15, N=4 for controls and N=5 for gpr56-injected embryos). Neuronal cell bodies shaded green. (r–u) Representative TEM images of the spinal cord in cross-section from 5 dpf control (r,s) and gpr56-injected (t,u) embryos. Scale bar, 1 μm. Quantification of total axon number (v), % myelinated axons (shaded blue, w, P<0.05) and myelin thickness on the large caliber Mauthner axon (shaded orange, x, P<0.008) in gpr56 OE embryos at 5 dpf relative to controls. SC, spinal cord. Student’s t-test used to test for statistical significance and error bars shown as±s.d. Two technical replicates were performed for each overexpression experiment.