UASt regulatory sequences drive expression of 'NaNuTrap' a nuclear-localized GFP-specific nanobody that draws GFP into the nucleus, permitting efficient cell labelling in vivo. The 'NaNuTrap' protein consists of three copies of the Tag:NLS(SV40-largeT) nuclear localization sequence, a six aspartate (6D) linker sequence and the VHH(GBP1) nanobody.