Figure 7. Fusion of SMN exon-7 to the nuclear protein, DBF1, targets it to the cytoplasm.

Left panels, EGFP fusion protein signal in nucleus (arrowhead) and cytoplasm (arrows). Right panels, Location of nuclear boundary (arrowheads) using DAPI (red).

A, An EGFP-DBF1 transfected neuron presented an exclusive nuclear localization of its EGFP fusion protein (arrowhead).

B, DAPI stained nucleus (red).

C, In contrast, an EGFP-DBF1/Ex7 transfected neuron showed fluorescence signal in the cytoplasm (arrow) beyond the (D) DAPI stained nucleus (red).

E, Proximal segment of exon-7 showed clear nucleus (arrowhead) with two foci and no evidence of EGFP signal accumulation. Cytoplasmic signal (arrows) in the perinuclear region was observed beyond the (F) DAPI stained nuclear border (red).

G, A similar pattern was observed when the middle segment of SMN exon-7 was fused to EGFP-DBF1.

H, DAPI (red).

I, In contrast, the distal segment of the exon-7 was present mostly in the nucleus (arrowhead) with some signal in the perinuclear region (arrow).

J, DAPI (red).

K, Quantitative analysis of subcellular localization showed the percent of transfected cells with only nuclear signal, signal in both the nucleus and cytoplasm (uniform), and only cytoplasmic signal.

L, Schematic of the three subregions of SMN exon-7 (P, proximal; M, middle; D, distal) that were fused to EGFP-DBF1.