Credit: Image: Courtesy of Dr. Maximiliano D'Angelo, Salk Institute for Biological Studies.
In aging cells one of the proteins composing nuclear pores becomes damaged and molecules that should be restricted to the cytoplasm invade the nucleus (outline shown in red). In particular, a protein called tubulin (shown in green), which is strictly a cytoplasmic protein, shows up as long filaments that co-opt a large part of the nucleus.