Over-expression of TOP IIβ rescues Nurr1 deficiency-induced neurite impairments in SH-SY5Y cells. A. The pRFP-C1 and pRFP-C1-Top IIβ plasmids were transfected to the Nurr1 knock-down stable cell line separately. Morphological changes were observed 3 days after transfection. Cells transfected with pRFP-C1 plasmids showed the same morphology as Nurr1 deficient cells, bearing occasionally very short neurites. pRFP-C1-Top IIβ plasmids express a RFP-fused TOP IIβ protein which located in the nucleus and induced neurites extension. B. After transfection for 3 days, pRFP-C1-Top IIβ plasmids increased TOP IIβ protein expression level of the cells significantly compared to the empty vectors. C. The average neurite length (total neurite length/cell number) was determined from more than 100 cells. Bars represent the mean ± SEM (n = 3 independent experiments). Neurite outgrowth in the pRFP-C1 and pRFP-C1-Top IIβ plasmids transfected Nurr1-deficiency cell line showed significant difference. **P <0.01 vs. empty vector. Bar = 20 μm.