Figure 4. An intact C-terminus facilitates nuclear export of patient FMRP.

1. Transfected HEK293 cells expressing GFP-tagged wild-type FMRP fused to the patient NLS motif (GFP-FMR1^wt+NLS). Unlike the patient FMRP, GFP-FMR1^wt+NLS protein is predominantly cytoplasmic and does not aggregate in the nucleus. However, treatment of HEK293 cells expressing GFP-FMR1^wt+NLS with leptomycin B—an inhibitor of nuclear export—resulted in the appearance of nucleolar inclusions. This suggests that the presence of a full-length C-terminus facilitates the nuclear export of FMRP in this context.
2. Transfected HEK293 cells expressing a modified version of GFP-tagged patient FMRP, in which the truncation of the C-terminus is reverted by restoring the open reading frame (GFP-FMR1^{G-ins.[Ct restored]}). The patient protein is not detected in the nucleus when the C-terminus is intact; however, nucleolar retention of the protein is observed upon leptomycin B treatment of the transfected cells. In line with results from (A), this suggests that an intact C-terminus enables nuclear export of the FMR1 protein.

Data information: Scale bar represents 10 μm.